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linux/fs/namespace.c
Al Viro b1983cd897 create_mnt_ns: unidiomatic use of list_add() 
while list_add(A, B) and list_add(B, A) are equivalent when both A and B
are guaranteed to be empty, the usual idiom is list_add(what, where),
not the other way round...  Not a bug per se, but only by accident and
it makes RTFS harder for no good reason.

Spotted-by: Rajat Sharma <fs.rajat@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2013-05-04 15:18:53 -04:00

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/*
* linux/fs/namespace.c
*
* (C) Copyright Al Viro 2000, 2001
* Released under GPL v2.
*
* Based on code from fs/super.c, copyright Linus Torvalds and others.
* Heavily rewritten.
*/
#include <linux/syscalls.h>
#include <linux/export.h>
#include <linux/capability.h>
#include <linux/mnt_namespace.h>
#include <linux/user_namespace.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/idr.h>
#include <linux/acct.h> /* acct_auto_close_mnt */
#include <linux/ramfs.h> /* init_rootfs */
#include <linux/fs_struct.h> /* get_fs_root et.al. */
#include <linux/fsnotify.h> /* fsnotify_vfsmount_delete */
#include <linux/uaccess.h>
#include <linux/proc_ns.h>
#include <linux/magic.h>
#include "pnode.h"
#include "internal.h"
#define HASH_SHIFT ilog2(PAGE_SIZE / sizeof(struct list_head))
#define HASH_SIZE (1UL << HASH_SHIFT)
static int event;
static DEFINE_IDA(mnt_id_ida);
static DEFINE_IDA(mnt_group_ida);
static DEFINE_SPINLOCK(mnt_id_lock);
static int mnt_id_start = 0;
static int mnt_group_start = 1;
static struct list_head *mount_hashtable __read_mostly;
static struct list_head *mountpoint_hashtable __read_mostly;
static struct kmem_cache *mnt_cache __read_mostly;
static struct rw_semaphore namespace_sem;
/* /sys/fs */
struct kobject *fs_kobj;
EXPORT_SYMBOL_GPL(fs_kobj);
/*
* vfsmount lock may be taken for read to prevent changes to the
* vfsmount hash, ie. during mountpoint lookups or walking back
* up the tree.
*
* It should be taken for write in all cases where the vfsmount
* tree or hash is modified or when a vfsmount structure is modified.
*/
DEFINE_BRLOCK(vfsmount_lock);
static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
{
unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
tmp = tmp + (tmp >> HASH_SHIFT);
return tmp & (HASH_SIZE - 1);
}
#define MNT_WRITER_UNDERFLOW_LIMIT -(1<<16)
/*
* allocation is serialized by namespace_sem, but we need the spinlock to
* serialize with freeing.
*/
static int mnt_alloc_id(struct mount *mnt)
{
int res;
retry:
ida_pre_get(&mnt_id_ida, GFP_KERNEL);
spin_lock(&mnt_id_lock);
res = ida_get_new_above(&mnt_id_ida, mnt_id_start, &mnt->mnt_id);
if (!res)
mnt_id_start = mnt->mnt_id + 1;
spin_unlock(&mnt_id_lock);
if (res == -EAGAIN)
goto retry;
return res;
}
static void mnt_free_id(struct mount *mnt)
{
int id = mnt->mnt_id;
spin_lock(&mnt_id_lock);
ida_remove(&mnt_id_ida, id);
if (mnt_id_start > id)
mnt_id_start = id;
spin_unlock(&mnt_id_lock);
}
/*
* Allocate a new peer group ID
*
* mnt_group_ida is protected by namespace_sem
*/
static int mnt_alloc_group_id(struct mount *mnt)
{
int res;
if (!ida_pre_get(&mnt_group_ida, GFP_KERNEL))
return -ENOMEM;
res = ida_get_new_above(&mnt_group_ida,
mnt_group_start,
&mnt->mnt_group_id);
if (!res)
mnt_group_start = mnt->mnt_group_id + 1;
return res;
}
/*
* Release a peer group ID
*/
void mnt_release_group_id(struct mount *mnt)
{
int id = mnt->mnt_group_id;
ida_remove(&mnt_group_ida, id);
if (mnt_group_start > id)
mnt_group_start = id;
mnt->mnt_group_id = 0;
}
/*
* vfsmount lock must be held for read
*/
static inline void mnt_add_count(struct mount *mnt, int n)
{
#ifdef CONFIG_SMP
this_cpu_add(mnt->mnt_pcp->mnt_count, n);
#else
preempt_disable();
mnt->mnt_count += n;
preempt_enable();
#endif
}
/*
* vfsmount lock must be held for write
*/
unsigned int mnt_get_count(struct mount *mnt)
{
#ifdef CONFIG_SMP
unsigned int count = 0;
int cpu;
for_each_possible_cpu(cpu) {
count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
}
return count;
#else
return mnt->mnt_count;
#endif
}
static struct mount *alloc_vfsmnt(const char *name)
{
struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
if (mnt) {
int err;
err = mnt_alloc_id(mnt);
if (err)
goto out_free_cache;
if (name) {
mnt->mnt_devname = kstrdup(name, GFP_KERNEL);
if (!mnt->mnt_devname)
goto out_free_id;
}
#ifdef CONFIG_SMP
mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
if (!mnt->mnt_pcp)
goto out_free_devname;
this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
#else
mnt->mnt_count = 1;
mnt->mnt_writers = 0;
#endif
INIT_LIST_HEAD(&mnt->mnt_hash);
INIT_LIST_HEAD(&mnt->mnt_child);
INIT_LIST_HEAD(&mnt->mnt_mounts);
INIT_LIST_HEAD(&mnt->mnt_list);
INIT_LIST_HEAD(&mnt->mnt_expire);
INIT_LIST_HEAD(&mnt->mnt_share);
INIT_LIST_HEAD(&mnt->mnt_slave_list);
INIT_LIST_HEAD(&mnt->mnt_slave);
#ifdef CONFIG_FSNOTIFY
INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
#endif
}
return mnt;
#ifdef CONFIG_SMP
out_free_devname:
kfree(mnt->mnt_devname);
#endif
out_free_id:
mnt_free_id(mnt);
out_free_cache:
kmem_cache_free(mnt_cache, mnt);
return NULL;
}
/*
* Most r/o checks on a fs are for operations that take
* discrete amounts of time, like a write() or unlink().
* We must keep track of when those operations start
* (for permission checks) and when they end, so that
* we can determine when writes are able to occur to
* a filesystem.
*/
/*
* __mnt_is_readonly: check whether a mount is read-only
* @mnt: the mount to check for its write status
*
* This shouldn't be used directly ouside of the VFS.
* It does not guarantee that the filesystem will stay
* r/w, just that it is right *now*. This can not and
* should not be used in place of IS_RDONLY(inode).
* mnt_want/drop_write() will _keep_ the filesystem
* r/w.
*/
int __mnt_is_readonly(struct vfsmount *mnt)
{
if (mnt->mnt_flags & MNT_READONLY)
return 1;
if (mnt->mnt_sb->s_flags & MS_RDONLY)
return 1;
return 0;
}
EXPORT_SYMBOL_GPL(__mnt_is_readonly);
static inline void mnt_inc_writers(struct mount *mnt)
{
#ifdef CONFIG_SMP
this_cpu_inc(mnt->mnt_pcp->mnt_writers);
#else
mnt->mnt_writers++;
#endif
}
static inline void mnt_dec_writers(struct mount *mnt)
{
#ifdef CONFIG_SMP
this_cpu_dec(mnt->mnt_pcp->mnt_writers);
#else
mnt->mnt_writers--;
#endif
}
static unsigned int mnt_get_writers(struct mount *mnt)
{
#ifdef CONFIG_SMP
unsigned int count = 0;
int cpu;
for_each_possible_cpu(cpu) {
count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
}
return count;
#else
return mnt->mnt_writers;
#endif
}
static int mnt_is_readonly(struct vfsmount *mnt)
{
if (mnt->mnt_sb->s_readonly_remount)
return 1;
/* Order wrt setting s_flags/s_readonly_remount in do_remount() */
smp_rmb();
return __mnt_is_readonly(mnt);
}
/*
* Most r/o & frozen checks on a fs are for operations that take discrete
* amounts of time, like a write() or unlink(). We must keep track of when
* those operations start (for permission checks) and when they end, so that we
* can determine when writes are able to occur to a filesystem.
*/
/**
* __mnt_want_write - get write access to a mount without freeze protection
* @m: the mount on which to take a write
*
* This tells the low-level filesystem that a write is about to be performed to
* it, and makes sure that writes are allowed (mnt it read-write) before
* returning success. This operation does not protect against filesystem being
* frozen. When the write operation is finished, __mnt_drop_write() must be
* called. This is effectively a refcount.
*/
int __mnt_want_write(struct vfsmount *m)
{
struct mount *mnt = real_mount(m);
int ret = 0;
preempt_disable();
mnt_inc_writers(mnt);
/*
* The store to mnt_inc_writers must be visible before we pass
* MNT_WRITE_HOLD loop below, so that the slowpath can see our
* incremented count after it has set MNT_WRITE_HOLD.
*/
smp_mb();
while (ACCESS_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
cpu_relax();
/*
* After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
* be set to match its requirements. So we must not load that until
* MNT_WRITE_HOLD is cleared.
*/
smp_rmb();
if (mnt_is_readonly(m)) {
mnt_dec_writers(mnt);
ret = -EROFS;
}
preempt_enable();
return ret;
}
/**
* mnt_want_write - get write access to a mount
* @m: the mount on which to take a write
*
* This tells the low-level filesystem that a write is about to be performed to
* it, and makes sure that writes are allowed (mount is read-write, filesystem
* is not frozen) before returning success. When the write operation is
* finished, mnt_drop_write() must be called. This is effectively a refcount.
*/
int mnt_want_write(struct vfsmount *m)
{
int ret;
sb_start_write(m->mnt_sb);
ret = __mnt_want_write(m);
if (ret)
sb_end_write(m->mnt_sb);
return ret;
}
EXPORT_SYMBOL_GPL(mnt_want_write);
/**
* mnt_clone_write - get write access to a mount
* @mnt: the mount on which to take a write
*
* This is effectively like mnt_want_write, except
* it must only be used to take an extra write reference
* on a mountpoint that we already know has a write reference
* on it. This allows some optimisation.
*
* After finished, mnt_drop_write must be called as usual to
* drop the reference.
*/
int mnt_clone_write(struct vfsmount *mnt)
{
/* superblock may be r/o */
if (__mnt_is_readonly(mnt))
return -EROFS;
preempt_disable();
mnt_inc_writers(real_mount(mnt));
preempt_enable();
return 0;
}
EXPORT_SYMBOL_GPL(mnt_clone_write);
/**
* __mnt_want_write_file - get write access to a file's mount
* @file: the file who's mount on which to take a write
*
* This is like __mnt_want_write, but it takes a file and can
* do some optimisations if the file is open for write already
*/
int __mnt_want_write_file(struct file *file)
{
struct inode *inode = file_inode(file);
if (!(file->f_mode & FMODE_WRITE) || special_file(inode->i_mode))
return __mnt_want_write(file->f_path.mnt);
else
return mnt_clone_write(file->f_path.mnt);
}
/**
* mnt_want_write_file - get write access to a file's mount
* @file: the file who's mount on which to take a write
*
* This is like mnt_want_write, but it takes a file and can
* do some optimisations if the file is open for write already
*/
int mnt_want_write_file(struct file *file)
{
int ret;
sb_start_write(file->f_path.mnt->mnt_sb);
ret = __mnt_want_write_file(file);
if (ret)
sb_end_write(file->f_path.mnt->mnt_sb);
return ret;
}
EXPORT_SYMBOL_GPL(mnt_want_write_file);
/**
* __mnt_drop_write - give up write access to a mount
* @mnt: the mount on which to give up write access
*
* Tells the low-level filesystem that we are done
* performing writes to it. Must be matched with
* __mnt_want_write() call above.
*/
void __mnt_drop_write(struct vfsmount *mnt)
{
preempt_disable();
mnt_dec_writers(real_mount(mnt));
preempt_enable();
}
/**
* mnt_drop_write - give up write access to a mount
* @mnt: the mount on which to give up write access
*
* Tells the low-level filesystem that we are done performing writes to it and
* also allows filesystem to be frozen again. Must be matched with
* mnt_want_write() call above.
*/
void mnt_drop_write(struct vfsmount *mnt)
{
__mnt_drop_write(mnt);
sb_end_write(mnt->mnt_sb);
}
EXPORT_SYMBOL_GPL(mnt_drop_write);
void __mnt_drop_write_file(struct file *file)
{
__mnt_drop_write(file->f_path.mnt);
}
void mnt_drop_write_file(struct file *file)
{
mnt_drop_write(file->f_path.mnt);
}
EXPORT_SYMBOL(mnt_drop_write_file);
static int mnt_make_readonly(struct mount *mnt)
{
int ret = 0;
br_write_lock(&vfsmount_lock);
mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
/*
* After storing MNT_WRITE_HOLD, we'll read the counters. This store
* should be visible before we do.
*/
smp_mb();
/*
* With writers on hold, if this value is zero, then there are
* definitely no active writers (although held writers may subsequently
* increment the count, they'll have to wait, and decrement it after
* seeing MNT_READONLY).
*
* It is OK to have counter incremented on one CPU and decremented on
* another: the sum will add up correctly. The danger would be when we
* sum up each counter, if we read a counter before it is incremented,
* but then read another CPU's count which it has been subsequently
* decremented from -- we would see more decrements than we should.
* MNT_WRITE_HOLD protects against this scenario, because
* mnt_want_write first increments count, then smp_mb, then spins on
* MNT_WRITE_HOLD, so it can't be decremented by another CPU while
* we're counting up here.
*/
if (mnt_get_writers(mnt) > 0)
ret = -EBUSY;
else
mnt->mnt.mnt_flags |= MNT_READONLY;
/*
* MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
* that become unheld will see MNT_READONLY.
*/
smp_wmb();
mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
br_write_unlock(&vfsmount_lock);
return ret;
}
static void __mnt_unmake_readonly(struct mount *mnt)
{
br_write_lock(&vfsmount_lock);
mnt->mnt.mnt_flags &= ~MNT_READONLY;
br_write_unlock(&vfsmount_lock);
}
int sb_prepare_remount_readonly(struct super_block *sb)
{
struct mount *mnt;
int err = 0;
/* Racy optimization. Recheck the counter under MNT_WRITE_HOLD */
if (atomic_long_read(&sb->s_remove_count))
return -EBUSY;
br_write_lock(&vfsmount_lock);
list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
smp_mb();
if (mnt_get_writers(mnt) > 0) {
err = -EBUSY;
break;
}
}
}
if (!err && atomic_long_read(&sb->s_remove_count))
err = -EBUSY;
if (!err) {
sb->s_readonly_remount = 1;
smp_wmb();
}
list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
if (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
}
br_write_unlock(&vfsmount_lock);
return err;
}
static void free_vfsmnt(struct mount *mnt)
{
kfree(mnt->mnt_devname);
mnt_free_id(mnt);
#ifdef CONFIG_SMP
free_percpu(mnt->mnt_pcp);
#endif
kmem_cache_free(mnt_cache, mnt);
}
/*
* find the first or last mount at @dentry on vfsmount @mnt depending on
* @dir. If @dir is set return the first mount else return the last mount.
* vfsmount_lock must be held for read or write.
*/
struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
int dir)
{
struct list_head *head = mount_hashtable + hash(mnt, dentry);
struct list_head *tmp = head;
struct mount *p, *found = NULL;
for (;;) {
tmp = dir ? tmp->next : tmp->prev;
p = NULL;
if (tmp == head)
break;
p = list_entry(tmp, struct mount, mnt_hash);
if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry) {
found = p;
break;
}
}
return found;
}
/*
* lookup_mnt - Return the first child mount mounted at path
*
* "First" means first mounted chronologically. If you create the
* following mounts:
*
* mount /dev/sda1 /mnt
* mount /dev/sda2 /mnt
* mount /dev/sda3 /mnt
*
* Then lookup_mnt() on the base /mnt dentry in the root mount will
* return successively the root dentry and vfsmount of /dev/sda1, then
* /dev/sda2, then /dev/sda3, then NULL.
*
* lookup_mnt takes a reference to the found vfsmount.
*/
struct vfsmount *lookup_mnt(struct path *path)
{
struct mount *child_mnt;
br_read_lock(&vfsmount_lock);
child_mnt = __lookup_mnt(path->mnt, path->dentry, 1);
if (child_mnt) {
mnt_add_count(child_mnt, 1);
br_read_unlock(&vfsmount_lock);
return &child_mnt->mnt;
} else {
br_read_unlock(&vfsmount_lock);
return NULL;
}
}
static struct mountpoint *new_mountpoint(struct dentry *dentry)
{
struct list_head *chain = mountpoint_hashtable + hash(NULL, dentry);
struct mountpoint *mp;
list_for_each_entry(mp, chain, m_hash) {
if (mp->m_dentry == dentry) {
/* might be worth a WARN_ON() */
if (d_unlinked(dentry))
return ERR_PTR(-ENOENT);
mp->m_count++;
return mp;
}
}
mp = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
if (!mp)
return ERR_PTR(-ENOMEM);
spin_lock(&dentry->d_lock);
if (d_unlinked(dentry)) {
spin_unlock(&dentry->d_lock);
kfree(mp);
return ERR_PTR(-ENOENT);
}
dentry->d_flags |= DCACHE_MOUNTED;
spin_unlock(&dentry->d_lock);
mp->m_dentry = dentry;
mp->m_count = 1;
list_add(&mp->m_hash, chain);
return mp;
}
static void put_mountpoint(struct mountpoint *mp)
{
if (!--mp->m_count) {
struct dentry *dentry = mp->m_dentry;
spin_lock(&dentry->d_lock);
dentry->d_flags &= ~DCACHE_MOUNTED;
spin_unlock(&dentry->d_lock);
list_del(&mp->m_hash);
kfree(mp);
}
}
static inline int check_mnt(struct mount *mnt)
{
return mnt->mnt_ns == current->nsproxy->mnt_ns;
}
/*
* vfsmount lock must be held for write
*/
static void touch_mnt_namespace(struct mnt_namespace *ns)
{
if (ns) {
ns->event = ++event;
wake_up_interruptible(&ns->poll);
}
}
/*
* vfsmount lock must be held for write
*/
static void __touch_mnt_namespace(struct mnt_namespace *ns)
{
if (ns && ns->event != event) {
ns->event = event;
wake_up_interruptible(&ns->poll);
}
}
/*
* vfsmount lock must be held for write
*/
static void detach_mnt(struct mount *mnt, struct path *old_path)
{
old_path->dentry = mnt->mnt_mountpoint;
old_path->mnt = &mnt->mnt_parent->mnt;
mnt->mnt_parent = mnt;
mnt->mnt_mountpoint = mnt->mnt.mnt_root;
list_del_init(&mnt->mnt_child);
list_del_init(&mnt->mnt_hash);
put_mountpoint(mnt->mnt_mp);
mnt->mnt_mp = NULL;
}
/*
* vfsmount lock must be held for write
*/
void mnt_set_mountpoint(struct mount *mnt,
struct mountpoint *mp,
struct mount *child_mnt)
{
mp->m_count++;
mnt_add_count(mnt, 1); /* essentially, that's mntget */
child_mnt->mnt_mountpoint = dget(mp->m_dentry);
child_mnt->mnt_parent = mnt;
child_mnt->mnt_mp = mp;
}
/*
* vfsmount lock must be held for write
*/
static void attach_mnt(struct mount *mnt,
struct mount *parent,
struct mountpoint *mp)
{
mnt_set_mountpoint(parent, mp, mnt);
list_add_tail(&mnt->mnt_hash, mount_hashtable +
hash(&parent->mnt, mp->m_dentry));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
}
/*
* vfsmount lock must be held for write
*/
static void commit_tree(struct mount *mnt)
{
struct mount *parent = mnt->mnt_parent;
struct mount *m;
LIST_HEAD(head);
struct mnt_namespace *n = parent->mnt_ns;
BUG_ON(parent == mnt);
list_add_tail(&head, &mnt->mnt_list);
list_for_each_entry(m, &head, mnt_list)
m->mnt_ns = n;
list_splice(&head, n->list.prev);
list_add_tail(&mnt->mnt_hash, mount_hashtable +
hash(&parent->mnt, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
touch_mnt_namespace(n);
}
static struct mount *next_mnt(struct mount *p, struct mount *root)
{
struct list_head *next = p->mnt_mounts.next;
if (next == &p->mnt_mounts) {
while (1) {
if (p == root)
return NULL;
next = p->mnt_child.next;
if (next != &p->mnt_parent->mnt_mounts)
break;
p = p->mnt_parent;
}
}
return list_entry(next, struct mount, mnt_child);
}
static struct mount *skip_mnt_tree(struct mount *p)
{
struct list_head *prev = p->mnt_mounts.prev;
while (prev != &p->mnt_mounts) {
p = list_entry(prev, struct mount, mnt_child);
prev = p->mnt_mounts.prev;
}
return p;
}
struct vfsmount *
vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
{
struct mount *mnt;
struct dentry *root;
if (!type)
return ERR_PTR(-ENODEV);
mnt = alloc_vfsmnt(name);
if (!mnt)
return ERR_PTR(-ENOMEM);
if (flags & MS_KERNMOUNT)
mnt->mnt.mnt_flags = MNT_INTERNAL;
root = mount_fs(type, flags, name, data);
if (IS_ERR(root)) {
free_vfsmnt(mnt);
return ERR_CAST(root);
}
mnt->mnt.mnt_root = root;
mnt->mnt.mnt_sb = root->d_sb;
mnt->mnt_mountpoint = mnt->mnt.mnt_root;
mnt->mnt_parent = mnt;
br_write_lock(&vfsmount_lock);
list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
br_write_unlock(&vfsmount_lock);
return &mnt->mnt;
}
EXPORT_SYMBOL_GPL(vfs_kern_mount);
static struct mount *clone_mnt(struct mount *old, struct dentry *root,
int flag)
{
struct super_block *sb = old->mnt.mnt_sb;
struct mount *mnt;
int err;
mnt = alloc_vfsmnt(old->mnt_devname);
if (!mnt)
return ERR_PTR(-ENOMEM);
if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
mnt->mnt_group_id = 0; /* not a peer of original */
else
mnt->mnt_group_id = old->mnt_group_id;
if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
err = mnt_alloc_group_id(mnt);
if (err)
goto out_free;
}
mnt->mnt.mnt_flags = old->mnt.mnt_flags & ~MNT_WRITE_HOLD;
/* Don't allow unprivileged users to change mount flags */
if ((flag & CL_UNPRIVILEGED) && (mnt->mnt.mnt_flags & MNT_READONLY))
mnt->mnt.mnt_flags |= MNT_LOCK_READONLY;
atomic_inc(&sb->s_active);
mnt->mnt.mnt_sb = sb;
mnt->mnt.mnt_root = dget(root);
mnt->mnt_mountpoint = mnt->mnt.mnt_root;
mnt->mnt_parent = mnt;
br_write_lock(&vfsmount_lock);
list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
br_write_unlock(&vfsmount_lock);
if ((flag & CL_SLAVE) ||
((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
list_add(&mnt->mnt_slave, &old->mnt_slave_list);
mnt->mnt_master = old;
CLEAR_MNT_SHARED(mnt);
} else if (!(flag & CL_PRIVATE)) {
if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
list_add(&mnt->mnt_share, &old->mnt_share);
if (IS_MNT_SLAVE(old))
list_add(&mnt->mnt_slave, &old->mnt_slave);
mnt->mnt_master = old->mnt_master;
}
if (flag & CL_MAKE_SHARED)
set_mnt_shared(mnt);
/* stick the duplicate mount on the same expiry list
* as the original if that was on one */
if (flag & CL_EXPIRE) {
if (!list_empty(&old->mnt_expire))
list_add(&mnt->mnt_expire, &old->mnt_expire);
}
return mnt;
out_free:
free_vfsmnt(mnt);
return ERR_PTR(err);
}
static inline void mntfree(struct mount *mnt)
{
struct vfsmount *m = &mnt->mnt;
struct super_block *sb = m->mnt_sb;
/*
* This probably indicates that somebody messed
* up a mnt_want/drop_write() pair. If this
* happens, the filesystem was probably unable
* to make r/w->r/o transitions.
*/
/*
* The locking used to deal with mnt_count decrement provides barriers,
* so mnt_get_writers() below is safe.
*/
WARN_ON(mnt_get_writers(mnt));
fsnotify_vfsmount_delete(m);
dput(m->mnt_root);
free_vfsmnt(mnt);
deactivate_super(sb);
}
static void mntput_no_expire(struct mount *mnt)
{
put_again:
#ifdef CONFIG_SMP
br_read_lock(&vfsmount_lock);
if (likely(mnt->mnt_ns)) {
/* shouldn't be the last one */
mnt_add_count(mnt, -1);
br_read_unlock(&vfsmount_lock);
return;
}
br_read_unlock(&vfsmount_lock);
br_write_lock(&vfsmount_lock);
mnt_add_count(mnt, -1);
if (mnt_get_count(mnt)) {
br_write_unlock(&vfsmount_lock);
return;
}
#else
mnt_add_count(mnt, -1);
if (likely(mnt_get_count(mnt)))
return;
br_write_lock(&vfsmount_lock);
#endif
if (unlikely(mnt->mnt_pinned)) {
mnt_add_count(mnt, mnt->mnt_pinned + 1);
mnt->mnt_pinned = 0;
br_write_unlock(&vfsmount_lock);
acct_auto_close_mnt(&mnt->mnt);
goto put_again;
}
list_del(&mnt->mnt_instance);
br_write_unlock(&vfsmount_lock);
mntfree(mnt);
}
void mntput(struct vfsmount *mnt)
{
if (mnt) {
struct mount *m = real_mount(mnt);
/* avoid cacheline pingpong, hope gcc doesn't get "smart" */
if (unlikely(m->mnt_expiry_mark))
m->mnt_expiry_mark = 0;
mntput_no_expire(m);
}
}
EXPORT_SYMBOL(mntput);
struct vfsmount *mntget(struct vfsmount *mnt)
{
if (mnt)
mnt_add_count(real_mount(mnt), 1);
return mnt;
}
EXPORT_SYMBOL(mntget);
void mnt_pin(struct vfsmount *mnt)
{
br_write_lock(&vfsmount_lock);
real_mount(mnt)->mnt_pinned++;
br_write_unlock(&vfsmount_lock);
}
EXPORT_SYMBOL(mnt_pin);
void mnt_unpin(struct vfsmount *m)
{
struct mount *mnt = real_mount(m);
br_write_lock(&vfsmount_lock);
if (mnt->mnt_pinned) {
mnt_add_count(mnt, 1);
mnt->mnt_pinned--;
}
br_write_unlock(&vfsmount_lock);
}
EXPORT_SYMBOL(mnt_unpin);
static inline void mangle(struct seq_file *m, const char *s)
{
seq_escape(m, s, " \t\n\\");
}
/*
* Simple .show_options callback for filesystems which don't want to
* implement more complex mount option showing.
*
* See also save_mount_options().
*/
int generic_show_options(struct seq_file *m, struct dentry *root)
{
const char *options;
rcu_read_lock();
options = rcu_dereference(root->d_sb->s_options);
if (options != NULL && options[0]) {
seq_putc(m, ',');
mangle(m, options);
}
rcu_read_unlock();
return 0;
}
EXPORT_SYMBOL(generic_show_options);
/*
* If filesystem uses generic_show_options(), this function should be
* called from the fill_super() callback.
*
* The .remount_fs callback usually needs to be handled in a special
* way, to make sure, that previous options are not overwritten if the
* remount fails.
*
* Also note, that if the filesystem's .remount_fs function doesn't
* reset all options to their default value, but changes only newly
* given options, then the displayed options will not reflect reality
* any more.
*/
void save_mount_options(struct super_block *sb, char *options)
{
BUG_ON(sb->s_options);
rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
}
EXPORT_SYMBOL(save_mount_options);
void replace_mount_options(struct super_block *sb, char *options)
{
char *old = sb->s_options;
rcu_assign_pointer(sb->s_options, options);
if (old) {
synchronize_rcu();
kfree(old);
}
}
EXPORT_SYMBOL(replace_mount_options);
#ifdef CONFIG_PROC_FS
/* iterator; we want it to have access to namespace_sem, thus here... */
static void *m_start(struct seq_file *m, loff_t *pos)
{
struct proc_mounts *p = proc_mounts(m);
down_read(&namespace_sem);
return seq_list_start(&p->ns->list, *pos);
}
static void *m_next(struct seq_file *m, void *v, loff_t *pos)
{
struct proc_mounts *p = proc_mounts(m);
return seq_list_next(v, &p->ns->list, pos);
}
static void m_stop(struct seq_file *m, void *v)
{
up_read(&namespace_sem);
}
static int m_show(struct seq_file *m, void *v)
{
struct proc_mounts *p = proc_mounts(m);
struct mount *r = list_entry(v, struct mount, mnt_list);
return p->show(m, &r->mnt);
}
const struct seq_operations mounts_op = {
.start = m_start,
.next = m_next,
.stop = m_stop,
.show = m_show,
};
#endif /* CONFIG_PROC_FS */
/**
* may_umount_tree - check if a mount tree is busy
* @mnt: root of mount tree
*
* This is called to check if a tree of mounts has any
* open files, pwds, chroots or sub mounts that are
* busy.
*/
int may_umount_tree(struct vfsmount *m)
{
struct mount *mnt = real_mount(m);
int actual_refs = 0;
int minimum_refs = 0;
struct mount *p;
BUG_ON(!m);
/* write lock needed for mnt_get_count */
br_write_lock(&vfsmount_lock);
for (p = mnt; p; p = next_mnt(p, mnt)) {
actual_refs += mnt_get_count(p);
minimum_refs += 2;
}
br_write_unlock(&vfsmount_lock);
if (actual_refs > minimum_refs)
return 0;
return 1;
}
EXPORT_SYMBOL(may_umount_tree);
/**
* may_umount - check if a mount point is busy
* @mnt: root of mount
*
* This is called to check if a mount point has any
* open files, pwds, chroots or sub mounts. If the
* mount has sub mounts this will return busy
* regardless of whether the sub mounts are busy.
*
* Doesn't take quota and stuff into account. IOW, in some cases it will
* give false negatives. The main reason why it's here is that we need
* a non-destructive way to look for easily umountable filesystems.
*/
int may_umount(struct vfsmount *mnt)
{
int ret = 1;
down_read(&namespace_sem);
br_write_lock(&vfsmount_lock);
if (propagate_mount_busy(real_mount(mnt), 2))
ret = 0;
br_write_unlock(&vfsmount_lock);
up_read(&namespace_sem);
return ret;
}
EXPORT_SYMBOL(may_umount);
static LIST_HEAD(unmounted); /* protected by namespace_sem */
static void namespace_unlock(void)
{
struct mount *mnt;
LIST_HEAD(head);
if (likely(list_empty(&unmounted))) {
up_write(&namespace_sem);
return;
}
list_splice_init(&unmounted, &head);
up_write(&namespace_sem);
while (!list_empty(&head)) {
mnt = list_first_entry(&head, struct mount, mnt_hash);
list_del_init(&mnt->mnt_hash);
if (mnt_has_parent(mnt)) {
struct dentry *dentry;
struct mount *m;
br_write_lock(&vfsmount_lock);
dentry = mnt->mnt_mountpoint;
m = mnt->mnt_parent;
mnt->mnt_mountpoint = mnt->mnt.mnt_root;
mnt->mnt_parent = mnt;
m->mnt_ghosts--;
br_write_unlock(&vfsmount_lock);
dput(dentry);
mntput(&m->mnt);
}
mntput(&mnt->mnt);
}
}
static inline void namespace_lock(void)
{
down_write(&namespace_sem);
}
/*
* vfsmount lock must be held for write
* namespace_sem must be held for write
*/
void umount_tree(struct mount *mnt, int propagate)
{
LIST_HEAD(tmp_list);
struct mount *p;
for (p = mnt; p; p = next_mnt(p, mnt))
list_move(&p->mnt_hash, &tmp_list);
if (propagate)
propagate_umount(&tmp_list);
list_for_each_entry(p, &tmp_list, mnt_hash) {
list_del_init(&p->mnt_expire);
list_del_init(&p->mnt_list);
__touch_mnt_namespace(p->mnt_ns);
p->mnt_ns = NULL;
list_del_init(&p->mnt_child);
if (mnt_has_parent(p)) {
p->mnt_parent->mnt_ghosts++;
put_mountpoint(p->mnt_mp);
p->mnt_mp = NULL;
}
change_mnt_propagation(p, MS_PRIVATE);
}
list_splice(&tmp_list, &unmounted);
}
static void shrink_submounts(struct mount *mnt);
static int do_umount(struct mount *mnt, int flags)
{
struct super_block *sb = mnt->mnt.mnt_sb;
int retval;
retval = security_sb_umount(&mnt->mnt, flags);
if (retval)
return retval;
/*
* Allow userspace to request a mountpoint be expired rather than
* unmounting unconditionally. Unmount only happens if:
* (1) the mark is already set (the mark is cleared by mntput())
* (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
*/
if (flags & MNT_EXPIRE) {
if (&mnt->mnt == current->fs->root.mnt ||
flags & (MNT_FORCE | MNT_DETACH))
return -EINVAL;
/*
* probably don't strictly need the lock here if we examined
* all race cases, but it's a slowpath.
*/
br_write_lock(&vfsmount_lock);
if (mnt_get_count(mnt) != 2) {
br_write_unlock(&vfsmount_lock);
return -EBUSY;
}
br_write_unlock(&vfsmount_lock);
if (!xchg(&mnt->mnt_expiry_mark, 1))
return -EAGAIN;
}
/*
* If we may have to abort operations to get out of this
* mount, and they will themselves hold resources we must
* allow the fs to do things. In the Unix tradition of
* 'Gee thats tricky lets do it in userspace' the umount_begin
* might fail to complete on the first run through as other tasks
* must return, and the like. Thats for the mount program to worry
* about for the moment.
*/
if (flags & MNT_FORCE && sb->s_op->umount_begin) {
sb->s_op->umount_begin(sb);
}
/*
* No sense to grab the lock for this test, but test itself looks
* somewhat bogus. Suggestions for better replacement?
* Ho-hum... In principle, we might treat that as umount + switch
* to rootfs. GC would eventually take care of the old vfsmount.
* Actually it makes sense, especially if rootfs would contain a
* /reboot - static binary that would close all descriptors and
* call reboot(9). Then init(8) could umount root and exec /reboot.
*/
if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
/*
* Special case for "unmounting" root ...
* we just try to remount it readonly.
*/
down_write(&sb->s_umount);
if (!(sb->s_flags & MS_RDONLY))
retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
up_write(&sb->s_umount);
return retval;
}
namespace_lock();
br_write_lock(&vfsmount_lock);
event++;
if (!(flags & MNT_DETACH))
shrink_submounts(mnt);
retval = -EBUSY;
if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
if (!list_empty(&mnt->mnt_list))
umount_tree(mnt, 1);
retval = 0;
}
br_write_unlock(&vfsmount_lock);
namespace_unlock();
return retval;
}
/*
* Is the caller allowed to modify his namespace?
*/
static inline bool may_mount(void)
{
return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
}
/*
* Now umount can handle mount points as well as block devices.
* This is important for filesystems which use unnamed block devices.
*
* We now support a flag for forced unmount like the other 'big iron'
* unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
*/
SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
{
struct path path;
struct mount *mnt;
int retval;
int lookup_flags = 0;
if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
return -EINVAL;
if (!may_mount())
return -EPERM;
if (!(flags & UMOUNT_NOFOLLOW))
lookup_flags |= LOOKUP_FOLLOW;
retval = user_path_at(AT_FDCWD, name, lookup_flags, &path);
if (retval)
goto out;
mnt = real_mount(path.mnt);
retval = -EINVAL;
if (path.dentry != path.mnt->mnt_root)
goto dput_and_out;
if (!check_mnt(mnt))
goto dput_and_out;
retval = do_umount(mnt, flags);
dput_and_out:
/* we mustn't call path_put() as that would clear mnt_expiry_mark */
dput(path.dentry);
mntput_no_expire(mnt);
out:
return retval;
}
#ifdef __ARCH_WANT_SYS_OLDUMOUNT
/*
* The 2.0 compatible umount. No flags.
*/
SYSCALL_DEFINE1(oldumount, char __user *, name)
{
return sys_umount(name, 0);
}
#endif
static bool mnt_ns_loop(struct path *path)
{
/* Could bind mounting the mount namespace inode cause a
* mount namespace loop?
*/
struct inode *inode = path->dentry->d_inode;
struct proc_ns *ei;
struct mnt_namespace *mnt_ns;
if (!proc_ns_inode(inode))
return false;
ei = get_proc_ns(inode);
if (ei->ns_ops != &mntns_operations)
return false;
mnt_ns = ei->ns;
return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
}
struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
int flag)
{
struct mount *res, *p, *q, *r, *parent;
if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
return ERR_PTR(-EINVAL);
res = q = clone_mnt(mnt, dentry, flag);
if (IS_ERR(q))
return q;
q->mnt_mountpoint = mnt->mnt_mountpoint;
p = mnt;
list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
struct mount *s;
if (!is_subdir(r->mnt_mountpoint, dentry))
continue;
for (s = r; s; s = next_mnt(s, r)) {
if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
s = skip_mnt_tree(s);
continue;
}
while (p != s->mnt_parent) {
p = p->mnt_parent;
q = q->mnt_parent;
}
p = s;
parent = q;
q = clone_mnt(p, p->mnt.mnt_root, flag);
if (IS_ERR(q))
goto out;
br_write_lock(&vfsmount_lock);
list_add_tail(&q->mnt_list, &res->mnt_list);
attach_mnt(q, parent, p->mnt_mp);
br_write_unlock(&vfsmount_lock);
}
}
return res;
out:
if (res) {
br_write_lock(&vfsmount_lock);
umount_tree(res, 0);
br_write_unlock(&vfsmount_lock);
}
return q;
}
/* Caller should check returned pointer for errors */
struct vfsmount *collect_mounts(struct path *path)
{
struct mount *tree;
namespace_lock();
tree = copy_tree(real_mount(path->mnt), path->dentry,
CL_COPY_ALL | CL_PRIVATE);
namespace_unlock();
if (IS_ERR(tree))
return NULL;
return &tree->mnt;
}
void drop_collected_mounts(struct vfsmount *mnt)
{
namespace_lock();
br_write_lock(&vfsmount_lock);
umount_tree(real_mount(mnt), 0);
br_write_unlock(&vfsmount_lock);
namespace_unlock();
}
int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
struct vfsmount *root)
{
struct mount *mnt;
int res = f(root, arg);
if (res)
return res;
list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
res = f(&mnt->mnt, arg);
if (res)
return res;
}
return 0;
}
static void cleanup_group_ids(struct mount *mnt, struct mount *end)
{
struct mount *p;
for (p = mnt; p != end; p = next_mnt(p, mnt)) {
if (p->mnt_group_id && !IS_MNT_SHARED(p))
mnt_release_group_id(p);
}
}
static int invent_group_ids(struct mount *mnt, bool recurse)
{
struct mount *p;
for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
int err = mnt_alloc_group_id(p);
if (err) {
cleanup_group_ids(mnt, p);
return err;
}
}
}
return 0;
}
/*
* @source_mnt : mount tree to be attached
* @nd : place the mount tree @source_mnt is attached
* @parent_nd : if non-null, detach the source_mnt from its parent and
* store the parent mount and mountpoint dentry.
* (done when source_mnt is moved)
*
* NOTE: in the table below explains the semantics when a source mount
* of a given type is attached to a destination mount of a given type.
* ---------------------------------------------------------------------------
* | BIND MOUNT OPERATION |
* |**************************************************************************
* | source-->| shared | private | slave | unbindable |
* | dest | | | | |
* | | | | | | |
* | v | | | | |
* |**************************************************************************
* | shared | shared (++) | shared (+) | shared(+++)| invalid |
* | | | | | |
* |non-shared| shared (+) | private | slave (*) | invalid |
* ***************************************************************************
* A bind operation clones the source mount and mounts the clone on the
* destination mount.
*
* (++) the cloned mount is propagated to all the mounts in the propagation
* tree of the destination mount and the cloned mount is added to
* the peer group of the source mount.
* (+) the cloned mount is created under the destination mount and is marked
* as shared. The cloned mount is added to the peer group of the source
* mount.
* (+++) the mount is propagated to all the mounts in the propagation tree
* of the destination mount and the cloned mount is made slave
* of the same master as that of the source mount. The cloned mount
* is marked as 'shared and slave'.
* (*) the cloned mount is made a slave of the same master as that of the
* source mount.
*
* ---------------------------------------------------------------------------
* | MOVE MOUNT OPERATION |
* |**************************************************************************
* | source-->| shared | private | slave | unbindable |
* | dest | | | | |
* | | | | | | |
* | v | | | | |
* |**************************************************************************
* | shared | shared (+) | shared (+) | shared(+++) | invalid |
* | | | | | |
* |non-shared| shared (+*) | private | slave (*) | unbindable |
* ***************************************************************************
*
* (+) the mount is moved to the destination. And is then propagated to
* all the mounts in the propagation tree of the destination mount.
* (+*) the mount is moved to the destination.
* (+++) the mount is moved to the destination and is then propagated to
* all the mounts belonging to the destination mount's propagation tree.
* the mount is marked as 'shared and slave'.
* (*) the mount continues to be a slave at the new location.
*
* if the source mount is a tree, the operations explained above is
* applied to each mount in the tree.
* Must be called without spinlocks held, since this function can sleep
* in allocations.
*/
static int attach_recursive_mnt(struct mount *source_mnt,
struct mount *dest_mnt,
struct mountpoint *dest_mp,
struct path *parent_path)
{
LIST_HEAD(tree_list);
struct mount *child, *p;
int err;
if (IS_MNT_SHARED(dest_mnt)) {
err = invent_group_ids(source_mnt, true);
if (err)
goto out;
}
err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
if (err)
goto out_cleanup_ids;
br_write_lock(&vfsmount_lock);
if (IS_MNT_SHARED(dest_mnt)) {
for (p = source_mnt; p; p = next_mnt(p, source_mnt))
set_mnt_shared(p);
}
if (parent_path) {
detach_mnt(source_mnt, parent_path);
attach_mnt(source_mnt, dest_mnt, dest_mp);
touch_mnt_namespace(source_mnt->mnt_ns);
} else {
mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
commit_tree(source_mnt);
}
list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
list_del_init(&child->mnt_hash);
commit_tree(child);
}
br_write_unlock(&vfsmount_lock);
return 0;
out_cleanup_ids:
if (IS_MNT_SHARED(dest_mnt))
cleanup_group_ids(source_mnt, NULL);
out:
return err;
}
static struct mountpoint *lock_mount(struct path *path)
{
struct vfsmount *mnt;
struct dentry *dentry = path->dentry;
retry:
mutex_lock(&dentry->d_inode->i_mutex);
if (unlikely(cant_mount(dentry))) {
mutex_unlock(&dentry->d_inode->i_mutex);
return ERR_PTR(-ENOENT);
}
namespace_lock();
mnt = lookup_mnt(path);
if (likely(!mnt)) {
struct mountpoint *mp = new_mountpoint(dentry);
if (IS_ERR(mp)) {
namespace_unlock();
mutex_unlock(&dentry->d_inode->i_mutex);
return mp;
}
return mp;
}
namespace_unlock();
mutex_unlock(&path->dentry->d_inode->i_mutex);
path_put(path);
path->mnt = mnt;
dentry = path->dentry = dget(mnt->mnt_root);
goto retry;
}
static void unlock_mount(struct mountpoint *where)
{
struct dentry *dentry = where->m_dentry;
put_mountpoint(where);
namespace_unlock();
mutex_unlock(&dentry->d_inode->i_mutex);
}
static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
{
if (mnt->mnt.mnt_sb->s_flags & MS_NOUSER)
return -EINVAL;
if (S_ISDIR(mp->m_dentry->d_inode->i_mode) !=
S_ISDIR(mnt->mnt.mnt_root->d_inode->i_mode))
return -ENOTDIR;
return attach_recursive_mnt(mnt, p, mp, NULL);
}
/*
* Sanity check the flags to change_mnt_propagation.
*/
static int flags_to_propagation_type(int flags)
{
int type = flags & ~(MS_REC | MS_SILENT);
/* Fail if any non-propagation flags are set */
if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
return 0;
/* Only one propagation flag should be set */
if (!is_power_of_2(type))
return 0;
return type;
}
/*
* recursively change the type of the mountpoint.
*/
static int do_change_type(struct path *path, int flag)
{
struct mount *m;
struct mount *mnt = real_mount(path->mnt);
int recurse = flag & MS_REC;
int type;
int err = 0;
if (path->dentry != path->mnt->mnt_root)
return -EINVAL;
type = flags_to_propagation_type(flag);
if (!type)
return -EINVAL;
namespace_lock();
if (type == MS_SHARED) {
err = invent_group_ids(mnt, recurse);
if (err)
goto out_unlock;
}
br_write_lock(&vfsmount_lock);
for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
change_mnt_propagation(m, type);
br_write_unlock(&vfsmount_lock);
out_unlock:
namespace_unlock();
return err;
}
/*
* do loopback mount.
*/
static int do_loopback(struct path *path, const char *old_name,
int recurse)
{
struct path old_path;
struct mount *mnt = NULL, *old, *parent;
struct mountpoint *mp;
int err;
if (!old_name || !*old_name)
return -EINVAL;
err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
if (err)
return err;
err = -EINVAL;
if (mnt_ns_loop(&old_path))
goto out;
mp = lock_mount(path);
err = PTR_ERR(mp);
if (IS_ERR(mp))
goto out;
old = real_mount(old_path.mnt);
parent = real_mount(path->mnt);
err = -EINVAL;
if (IS_MNT_UNBINDABLE(old))
goto out2;
if (!check_mnt(parent) || !check_mnt(old))
goto out2;
if (recurse)
mnt = copy_tree(old, old_path.dentry, 0);
else
mnt = clone_mnt(old, old_path.dentry, 0);
if (IS_ERR(mnt)) {
err = PTR_ERR(mnt);
goto out2;
}
err = graft_tree(mnt, parent, mp);
if (err) {
br_write_lock(&vfsmount_lock);
umount_tree(mnt, 0);
br_write_unlock(&vfsmount_lock);
}
out2:
unlock_mount(mp);
out:
path_put(&old_path);
return err;
}
static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
{
int error = 0;
int readonly_request = 0;
if (ms_flags & MS_RDONLY)
readonly_request = 1;
if (readonly_request == __mnt_is_readonly(mnt))
return 0;
if (mnt->mnt_flags & MNT_LOCK_READONLY)
return -EPERM;
if (readonly_request)
error = mnt_make_readonly(real_mount(mnt));
else
__mnt_unmake_readonly(real_mount(mnt));
return error;
}
/*
* change filesystem flags. dir should be a physical root of filesystem.
* If you've mounted a non-root directory somewhere and want to do remount
* on it - tough luck.
*/
static int do_remount(struct path *path, int flags, int mnt_flags,
void *data)
{
int err;
struct super_block *sb = path->mnt->mnt_sb;
struct mount *mnt = real_mount(path->mnt);
if (!check_mnt(mnt))
return -EINVAL;
if (path->dentry != path->mnt->mnt_root)
return -EINVAL;
err = security_sb_remount(sb, data);
if (err)
return err;
down_write(&sb->s_umount);
if (flags & MS_BIND)
err = change_mount_flags(path->mnt, flags);
else if (!capable(CAP_SYS_ADMIN))
err = -EPERM;
else
err = do_remount_sb(sb, flags, data, 0);
if (!err) {
br_write_lock(&vfsmount_lock);
mnt_flags |= mnt->mnt.mnt_flags & MNT_PROPAGATION_MASK;
mnt->mnt.mnt_flags = mnt_flags;
br_write_unlock(&vfsmount_lock);
}
up_write(&sb->s_umount);
if (!err) {
br_write_lock(&vfsmount_lock);
touch_mnt_namespace(mnt->mnt_ns);
br_write_unlock(&vfsmount_lock);
}
return err;
}
static inline int tree_contains_unbindable(struct mount *mnt)
{
struct mount *p;
for (p = mnt; p; p = next_mnt(p, mnt)) {
if (IS_MNT_UNBINDABLE(p))
return 1;
}
return 0;
}
static int do_move_mount(struct path *path, const char *old_name)
{
struct path old_path, parent_path;
struct mount *p;
struct mount *old;
struct mountpoint *mp;
int err;
if (!old_name || !*old_name)
return -EINVAL;
err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
if (err)
return err;
mp = lock_mount(path);
err = PTR_ERR(mp);
if (IS_ERR(mp))
goto out;
old = real_mount(old_path.mnt);
p = real_mount(path->mnt);
err = -EINVAL;
if (!check_mnt(p) || !check_mnt(old))
goto out1;
err = -EINVAL;
if (old_path.dentry != old_path.mnt->mnt_root)
goto out1;
if (!mnt_has_parent(old))
goto out1;
if (S_ISDIR(path->dentry->d_inode->i_mode) !=
S_ISDIR(old_path.dentry->d_inode->i_mode))
goto out1;
/*
* Don't move a mount residing in a shared parent.
*/
if (IS_MNT_SHARED(old->mnt_parent))
goto out1;
/*
* Don't move a mount tree containing unbindable mounts to a destination
* mount which is shared.
*/
if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
goto out1;
err = -ELOOP;
for (; mnt_has_parent(p); p = p->mnt_parent)
if (p == old)
goto out1;
err = attach_recursive_mnt(old, real_mount(path->mnt), mp, &parent_path);
if (err)
goto out1;
/* if the mount is moved, it should no longer be expire
* automatically */
list_del_init(&old->mnt_expire);
out1:
unlock_mount(mp);
out:
if (!err)
path_put(&parent_path);
path_put(&old_path);
return err;
}
static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
{
int err;
const char *subtype = strchr(fstype, '.');
if (subtype) {
subtype++;
err = -EINVAL;
if (!subtype[0])
goto err;
} else
subtype = "";
mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
err = -ENOMEM;
if (!mnt->mnt_sb->s_subtype)
goto err;
return mnt;
err:
mntput(mnt);
return ERR_PTR(err);
}
/*
* add a mount into a namespace's mount tree
*/
static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
{
struct mountpoint *mp;
struct mount *parent;
int err;
mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL);
mp = lock_mount(path);
if (IS_ERR(mp))
return PTR_ERR(mp);
parent = real_mount(path->mnt);
err = -EINVAL;
if (unlikely(!check_mnt(parent))) {
/* that's acceptable only for automounts done in private ns */
if (!(mnt_flags & MNT_SHRINKABLE))
goto unlock;
/* ... and for those we'd better have mountpoint still alive */
if (!parent->mnt_ns)
goto unlock;
}
/* Refuse the same filesystem on the same mount point */
err = -EBUSY;
if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
path->mnt->mnt_root == path->dentry)
goto unlock;
err = -EINVAL;
if (S_ISLNK(newmnt->mnt.mnt_root->d_inode->i_mode))
goto unlock;
newmnt->mnt.mnt_flags = mnt_flags;
err = graft_tree(newmnt, parent, mp);
unlock:
unlock_mount(mp);
return err;
}
/*
* create a new mount for userspace and request it to be added into the
* namespace's tree
*/
static int do_new_mount(struct path *path, const char *fstype, int flags,
int mnt_flags, const char *name, void *data)
{
struct file_system_type *type;
struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
struct vfsmount *mnt;
int err;
if (!fstype)
return -EINVAL;
type = get_fs_type(fstype);
if (!type)
return -ENODEV;
if (user_ns != &init_user_ns) {
if (!(type->fs_flags & FS_USERNS_MOUNT)) {
put_filesystem(type);
return -EPERM;
}
/* Only in special cases allow devices from mounts
* created outside the initial user namespace.
*/
if (!(type->fs_flags & FS_USERNS_DEV_MOUNT)) {
flags |= MS_NODEV;
mnt_flags |= MNT_NODEV;
}
}
mnt = vfs_kern_mount(type, flags, name, data);
if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
!mnt->mnt_sb->s_subtype)
mnt = fs_set_subtype(mnt, fstype);
put_filesystem(type);
if (IS_ERR(mnt))
return PTR_ERR(mnt);
err = do_add_mount(real_mount(mnt), path, mnt_flags);
if (err)
mntput(mnt);
return err;
}
int finish_automount(struct vfsmount *m, struct path *path)
{
struct mount *mnt = real_mount(m);
int err;
/* The new mount record should have at least 2 refs to prevent it being
* expired before we get a chance to add it
*/
BUG_ON(mnt_get_count(mnt) < 2);
if (m->mnt_sb == path->mnt->mnt_sb &&
m->mnt_root == path->dentry) {
err = -ELOOP;
goto fail;
}
err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
if (!err)
return 0;
fail:
/* remove m from any expiration list it may be on */
if (!list_empty(&mnt->mnt_expire)) {
namespace_lock();
br_write_lock(&vfsmount_lock);
list_del_init(&mnt->mnt_expire);
br_write_unlock(&vfsmount_lock);
namespace_unlock();
}
mntput(m);
mntput(m);
return err;
}
/**
* mnt_set_expiry - Put a mount on an expiration list
* @mnt: The mount to list.
* @expiry_list: The list to add the mount to.
*/
void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
{
namespace_lock();
br_write_lock(&vfsmount_lock);
list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
br_write_unlock(&vfsmount_lock);
namespace_unlock();
}
EXPORT_SYMBOL(mnt_set_expiry);
/*
* process a list of expirable mountpoints with the intent of discarding any
* mountpoints that aren't in use and haven't been touched since last we came
* here
*/
void mark_mounts_for_expiry(struct list_head *mounts)
{
struct mount *mnt, *next;
LIST_HEAD(graveyard);
if (list_empty(mounts))
return;
namespace_lock();
br_write_lock(&vfsmount_lock);
/* extract from the expiration list every vfsmount that matches the
* following criteria:
* - only referenced by its parent vfsmount
* - still marked for expiry (marked on the last call here; marks are
* cleared by mntput())
*/
list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
if (!xchg(&mnt->mnt_expiry_mark, 1) ||
propagate_mount_busy(mnt, 1))
continue;
list_move(&mnt->mnt_expire, &graveyard);
}
while (!list_empty(&graveyard)) {
mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
touch_mnt_namespace(mnt->mnt_ns);
umount_tree(mnt, 1);
}
br_write_unlock(&vfsmount_lock);
namespace_unlock();
}
EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
/*
* Ripoff of 'select_parent()'
*
* search the list of submounts for a given mountpoint, and move any
* shrinkable submounts to the 'graveyard' list.
*/
static int select_submounts(struct mount *parent, struct list_head *graveyard)
{
struct mount *this_parent = parent;
struct list_head *next;
int found = 0;
repeat:
next = this_parent->mnt_mounts.next;
resume:
while (next != &this_parent->mnt_mounts) {
struct list_head *tmp = next;
struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
next = tmp->next;
if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
continue;
/*
* Descend a level if the d_mounts list is non-empty.
*/
if (!list_empty(&mnt->mnt_mounts)) {
this_parent = mnt;
goto repeat;
}
if (!propagate_mount_busy(mnt, 1)) {
list_move_tail(&mnt->mnt_expire, graveyard);
found++;
}
}
/*
* All done at this level ... ascend and resume the search
*/
if (this_parent != parent) {
next = this_parent->mnt_child.next;
this_parent = this_parent->mnt_parent;
goto resume;
}
return found;
}
/*
* process a list of expirable mountpoints with the intent of discarding any
* submounts of a specific parent mountpoint
*
* vfsmount_lock must be held for write
*/
static void shrink_submounts(struct mount *mnt)
{
LIST_HEAD(graveyard);
struct mount *m;
/* extract submounts of 'mountpoint' from the expiration list */
while (select_submounts(mnt, &graveyard)) {
while (!list_empty(&graveyard)) {
m = list_first_entry(&graveyard, struct mount,
mnt_expire);
touch_mnt_namespace(m->mnt_ns);
umount_tree(m, 1);
}
}
}
/*
* Some copy_from_user() implementations do not return the exact number of
* bytes remaining to copy on a fault. But copy_mount_options() requires that.
* Note that this function differs from copy_from_user() in that it will oops
* on bad values of `to', rather than returning a short copy.
*/
static long exact_copy_from_user(void *to, const void __user * from,
unsigned long n)
{
char *t = to;
const char __user *f = from;
char c;
if (!access_ok(VERIFY_READ, from, n))
return n;
while (n) {
if (__get_user(c, f)) {
memset(t, 0, n);
break;
}
*t++ = c;
f++;
n--;
}
return n;
}
int copy_mount_options(const void __user * data, unsigned long *where)
{
int i;
unsigned long page;
unsigned long size;
*where = 0;
if (!data)
return 0;
if (!(page = __get_free_page(GFP_KERNEL)))
return -ENOMEM;
/* We only care that *some* data at the address the user
* gave us is valid. Just in case, we'll zero
* the remainder of the page.
*/
/* copy_from_user cannot cross TASK_SIZE ! */
size = TASK_SIZE - (unsigned long)data;
if (size > PAGE_SIZE)
size = PAGE_SIZE;
i = size - exact_copy_from_user((void *)page, data, size);
if (!i) {
free_page(page);
return -EFAULT;
}
if (i != PAGE_SIZE)
memset((char *)page + i, 0, PAGE_SIZE - i);
*where = page;
return 0;
}
int copy_mount_string(const void __user *data, char **where)
{
char *tmp;
if (!data) {
*where = NULL;
return 0;
}
tmp = strndup_user(data, PAGE_SIZE);
if (IS_ERR(tmp))
return PTR_ERR(tmp);
*where = tmp;
return 0;
}
/*
* Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
* be given to the mount() call (ie: read-only, no-dev, no-suid etc).
*
* data is a (void *) that can point to any structure up to
* PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
* information (or be NULL).
*
* Pre-0.97 versions of mount() didn't have a flags word.
* When the flags word was introduced its top half was required
* to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
* Therefore, if this magic number is present, it carries no information
* and must be discarded.
*/
long do_mount(const char *dev_name, const char *dir_name,
const char *type_page, unsigned long flags, void *data_page)
{
struct path path;
int retval = 0;
int mnt_flags = 0;
/* Discard magic */
if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
flags &= ~MS_MGC_MSK;
/* Basic sanity checks */
if (!dir_name || !*dir_name || !memchr(dir_name, 0, PAGE_SIZE))
return -EINVAL;
if (data_page)
((char *)data_page)[PAGE_SIZE - 1] = 0;
/* ... and get the mountpoint */
retval = kern_path(dir_name, LOOKUP_FOLLOW, &path);
if (retval)
return retval;
retval = security_sb_mount(dev_name, &path,
type_page, flags, data_page);
if (!retval && !may_mount())
retval = -EPERM;
if (retval)
goto dput_out;
/* Default to relatime unless overriden */
if (!(flags & MS_NOATIME))
mnt_flags |= MNT_RELATIME;
/* Separate the per-mountpoint flags */
if (flags & MS_NOSUID)
mnt_flags |= MNT_NOSUID;
if (flags & MS_NODEV)
mnt_flags |= MNT_NODEV;
if (flags & MS_NOEXEC)
mnt_flags |= MNT_NOEXEC;
if (flags & MS_NOATIME)
mnt_flags |= MNT_NOATIME;
if (flags & MS_NODIRATIME)
mnt_flags |= MNT_NODIRATIME;
if (flags & MS_STRICTATIME)
mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
if (flags & MS_RDONLY)
mnt_flags |= MNT_READONLY;
flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
MS_STRICTATIME);
if (flags & MS_REMOUNT)
retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,
data_page);
else if (flags & MS_BIND)
retval = do_loopback(&path, dev_name, flags & MS_REC);
else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
retval = do_change_type(&path, flags);
else if (flags & MS_MOVE)
retval = do_move_mount(&path, dev_name);
else
retval = do_new_mount(&path, type_page, flags, mnt_flags,
dev_name, data_page);
dput_out:
path_put(&path);
return retval;
}
static void free_mnt_ns(struct mnt_namespace *ns)
{
proc_free_inum(ns->proc_inum);
put_user_ns(ns->user_ns);
kfree(ns);
}
/*
* Assign a sequence number so we can detect when we attempt to bind
* mount a reference to an older mount namespace into the current
* mount namespace, preventing reference counting loops. A 64bit
* number incrementing at 10Ghz will take 12,427 years to wrap which
* is effectively never, so we can ignore the possibility.
*/
static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
{
struct mnt_namespace *new_ns;
int ret;
new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
if (!new_ns)
return ERR_PTR(-ENOMEM);
ret = proc_alloc_inum(&new_ns->proc_inum);
if (ret) {
kfree(new_ns);
return ERR_PTR(ret);
}
new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
atomic_set(&new_ns->count, 1);
new_ns->root = NULL;
INIT_LIST_HEAD(&new_ns->list);
init_waitqueue_head(&new_ns->poll);
new_ns->event = 0;
new_ns->user_ns = get_user_ns(user_ns);
return new_ns;
}
/*
* Allocate a new namespace structure and populate it with contents
* copied from the namespace of the passed in task structure.
*/
static struct mnt_namespace *dup_mnt_ns(struct mnt_namespace *mnt_ns,
struct user_namespace *user_ns, struct fs_struct *fs)
{
struct mnt_namespace *new_ns;
struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
struct mount *p, *q;
struct mount *old = mnt_ns->root;
struct mount *new;
int copy_flags;
new_ns = alloc_mnt_ns(user_ns);
if (IS_ERR(new_ns))
return new_ns;
namespace_lock();
/* First pass: copy the tree topology */
copy_flags = CL_COPY_ALL | CL_EXPIRE;
if (user_ns != mnt_ns->user_ns)
copy_flags |= CL_SHARED_TO_SLAVE | CL_UNPRIVILEGED;
new = copy_tree(old, old->mnt.mnt_root, copy_flags);
if (IS_ERR(new)) {
namespace_unlock();
free_mnt_ns(new_ns);
return ERR_CAST(new);
}
new_ns->root = new;
br_write_lock(&vfsmount_lock);
list_add_tail(&new_ns->list, &new->mnt_list);
br_write_unlock(&vfsmount_lock);
/*
* Second pass: switch the tsk->fs->* elements and mark new vfsmounts
* as belonging to new namespace. We have already acquired a private
* fs_struct, so tsk->fs->lock is not needed.
*/
p = old;
q = new;
while (p) {
q->mnt_ns = new_ns;
if (fs) {
if (&p->mnt == fs->root.mnt) {
fs->root.mnt = mntget(&q->mnt);
rootmnt = &p->mnt;
}
if (&p->mnt == fs->pwd.mnt) {
fs->pwd.mnt = mntget(&q->mnt);
pwdmnt = &p->mnt;
}
}
p = next_mnt(p, old);
q = next_mnt(q, new);
}
namespace_unlock();
if (rootmnt)
mntput(rootmnt);
if (pwdmnt)
mntput(pwdmnt);
return new_ns;
}
struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
struct user_namespace *user_ns, struct fs_struct *new_fs)
{
struct mnt_namespace *new_ns;
BUG_ON(!ns);
get_mnt_ns(ns);
if (!(flags & CLONE_NEWNS))
return ns;
new_ns = dup_mnt_ns(ns, user_ns, new_fs);
put_mnt_ns(ns);
return new_ns;
}
/**
* create_mnt_ns - creates a private namespace and adds a root filesystem
* @mnt: pointer to the new root filesystem mountpoint
*/
static struct mnt_namespace *create_mnt_ns(struct vfsmount *m)
{
struct mnt_namespace *new_ns = alloc_mnt_ns(&init_user_ns);
if (!IS_ERR(new_ns)) {
struct mount *mnt = real_mount(m);
mnt->mnt_ns = new_ns;
new_ns->root = mnt;
list_add(&mnt->mnt_list, &new_ns->list);
} else {
mntput(m);
}
return new_ns;
}
struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
{
struct mnt_namespace *ns;
struct super_block *s;
struct path path;
int err;
ns = create_mnt_ns(mnt);
if (IS_ERR(ns))
return ERR_CAST(ns);
err = vfs_path_lookup(mnt->mnt_root, mnt,
name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
put_mnt_ns(ns);
if (err)
return ERR_PTR(err);
/* trade a vfsmount reference for active sb one */
s = path.mnt->mnt_sb;
atomic_inc(&s->s_active);
mntput(path.mnt);
/* lock the sucker */
down_write(&s->s_umount);
/* ... and return the root of (sub)tree on it */
return path.dentry;
}
EXPORT_SYMBOL(mount_subtree);
SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
char __user *, type, unsigned long, flags, void __user *, data)
{
int ret;
char *kernel_type;
struct filename *kernel_dir;
char *kernel_dev;
unsigned long data_page;
ret = copy_mount_string(type, &kernel_type);
if (ret < 0)
goto out_type;
kernel_dir = getname(dir_name);
if (IS_ERR(kernel_dir)) {
ret = PTR_ERR(kernel_dir);
goto out_dir;
}
ret = copy_mount_string(dev_name, &kernel_dev);
if (ret < 0)
goto out_dev;
ret = copy_mount_options(data, &data_page);
if (ret < 0)
goto out_data;
ret = do_mount(kernel_dev, kernel_dir->name, kernel_type, flags,
(void *) data_page);
free_page(data_page);
out_data:
kfree(kernel_dev);
out_dev:
putname(kernel_dir);
out_dir:
kfree(kernel_type);
out_type:
return ret;
}
/*
* Return true if path is reachable from root
*
* namespace_sem or vfsmount_lock is held
*/
bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
const struct path *root)
{
while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
dentry = mnt->mnt_mountpoint;
mnt = mnt->mnt_parent;
}
return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
}
int path_is_under(struct path *path1, struct path *path2)
{
int res;
br_read_lock(&vfsmount_lock);
res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
br_read_unlock(&vfsmount_lock);
return res;
}
EXPORT_SYMBOL(path_is_under);
/*
* pivot_root Semantics:
* Moves the root file system of the current process to the directory put_old,
* makes new_root as the new root file system of the current process, and sets
* root/cwd of all processes which had them on the current root to new_root.
*
* Restrictions:
* The new_root and put_old must be directories, and must not be on the
* same file system as the current process root. The put_old must be
* underneath new_root, i.e. adding a non-zero number of /.. to the string
* pointed to by put_old must yield the same directory as new_root. No other
* file system may be mounted on put_old. After all, new_root is a mountpoint.
*
* Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
* See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
* in this situation.
*
* Notes:
* - we don't move root/cwd if they are not at the root (reason: if something
* cared enough to change them, it's probably wrong to force them elsewhere)
* - it's okay to pick a root that isn't the root of a file system, e.g.
* /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
* though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
* first.
*/
SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
const char __user *, put_old)
{
struct path new, old, parent_path, root_parent, root;
struct mount *new_mnt, *root_mnt, *old_mnt;
struct mountpoint *old_mp, *root_mp;
int error;
if (!may_mount())
return -EPERM;
error = user_path_dir(new_root, &new);
if (error)
goto out0;
error = user_path_dir(put_old, &old);
if (error)
goto out1;
error = security_sb_pivotroot(&old, &new);
if (error)
goto out2;
get_fs_root(current->fs, &root);
old_mp = lock_mount(&old);
error = PTR_ERR(old_mp);
if (IS_ERR(old_mp))
goto out3;
error = -EINVAL;
new_mnt = real_mount(new.mnt);
root_mnt = real_mount(root.mnt);
old_mnt = real_mount(old.mnt);
if (IS_MNT_SHARED(old_mnt) ||
IS_MNT_SHARED(new_mnt->mnt_parent) ||
IS_MNT_SHARED(root_mnt->mnt_parent))
goto out4;
if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
goto out4;
error = -ENOENT;
if (d_unlinked(new.dentry))
goto out4;
error = -EBUSY;
if (new_mnt == root_mnt || old_mnt == root_mnt)
goto out4; /* loop, on the same file system */
error = -EINVAL;
if (root.mnt->mnt_root != root.dentry)
goto out4; /* not a mountpoint */
if (!mnt_has_parent(root_mnt))
goto out4; /* not attached */
root_mp = root_mnt->mnt_mp;
if (new.mnt->mnt_root != new.dentry)
goto out4; /* not a mountpoint */
if (!mnt_has_parent(new_mnt))
goto out4; /* not attached */
/* make sure we can reach put_old from new_root */
if (!is_path_reachable(old_mnt, old.dentry, &new))
goto out4;
root_mp->m_count++; /* pin it so it won't go away */
br_write_lock(&vfsmount_lock);
detach_mnt(new_mnt, &parent_path);
detach_mnt(root_mnt, &root_parent);
/* mount old root on put_old */
attach_mnt(root_mnt, old_mnt, old_mp);
/* mount new_root on / */
attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
touch_mnt_namespace(current->nsproxy->mnt_ns);
br_write_unlock(&vfsmount_lock);
chroot_fs_refs(&root, &new);
put_mountpoint(root_mp);
error = 0;
out4:
unlock_mount(old_mp);
if (!error) {
path_put(&root_parent);
path_put(&parent_path);
}
out3:
path_put(&root);
out2:
path_put(&old);
out1:
path_put(&new);
out0:
return error;
}
static void __init init_mount_tree(void)
{
struct vfsmount *mnt;
struct mnt_namespace *ns;
struct path root;
struct file_system_type *type;
type = get_fs_type("rootfs");
if (!type)
panic("Can't find rootfs type");
mnt = vfs_kern_mount(type, 0, "rootfs", NULL);
put_filesystem(type);
if (IS_ERR(mnt))
panic("Can't create rootfs");
ns = create_mnt_ns(mnt);
if (IS_ERR(ns))
panic("Can't allocate initial namespace");
init_task.nsproxy->mnt_ns = ns;
get_mnt_ns(ns);
root.mnt = mnt;
root.dentry = mnt->mnt_root;
set_fs_pwd(current->fs, &root);
set_fs_root(current->fs, &root);
}
void __init mnt_init(void)
{
unsigned u;
int err;
init_rwsem(&namespace_sem);
mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
mountpoint_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
if (!mount_hashtable || !mountpoint_hashtable)
panic("Failed to allocate mount hash table\n");
printk(KERN_INFO "Mount-cache hash table entries: %lu\n", HASH_SIZE);
for (u = 0; u < HASH_SIZE; u++)
INIT_LIST_HEAD(&mount_hashtable[u]);
for (u = 0; u < HASH_SIZE; u++)
INIT_LIST_HEAD(&mountpoint_hashtable[u]);
br_lock_init(&vfsmount_lock);
err = sysfs_init();
if (err)
printk(KERN_WARNING "%s: sysfs_init error: %d\n",
__func__, err);
fs_kobj = kobject_create_and_add("fs", NULL);
if (!fs_kobj)
printk(KERN_WARNING "%s: kobj create error\n", __func__);
init_rootfs();
init_mount_tree();
}
void put_mnt_ns(struct mnt_namespace *ns)
{
if (!atomic_dec_and_test(&ns->count))
return;
namespace_lock();
br_write_lock(&vfsmount_lock);
umount_tree(ns->root, 0);
br_write_unlock(&vfsmount_lock);
namespace_unlock();
free_mnt_ns(ns);
}
struct vfsmount *kern_mount_data(struct file_system_type *type, void *data)
{
struct vfsmount *mnt;
mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data);
if (!IS_ERR(mnt)) {
/*
* it is a longterm mount, don't release mnt until
* we unmount before file sys is unregistered
*/
real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
}
return mnt;
}
EXPORT_SYMBOL_GPL(kern_mount_data);
void kern_unmount(struct vfsmount *mnt)
{
/* release long term mount so mount point can be released */
if (!IS_ERR_OR_NULL(mnt)) {
br_write_lock(&vfsmount_lock);
real_mount(mnt)->mnt_ns = NULL;
br_write_unlock(&vfsmount_lock);
mntput(mnt);
}
}
EXPORT_SYMBOL(kern_unmount);
bool our_mnt(struct vfsmount *mnt)
{
return check_mnt(real_mount(mnt));
}
bool current_chrooted(void)
{
/* Does the current process have a non-standard root */
struct path ns_root;
struct path fs_root;
bool chrooted;
/* Find the namespace root */
ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
ns_root.dentry = ns_root.mnt->mnt_root;
path_get(&ns_root);
while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
;
get_fs_root(current->fs, &fs_root);
chrooted = !path_equal(&fs_root, &ns_root);
path_put(&fs_root);
path_put(&ns_root);
return chrooted;
}
void update_mnt_policy(struct user_namespace *userns)
{
struct mnt_namespace *ns = current->nsproxy->mnt_ns;
struct mount *mnt;
down_read(&namespace_sem);
list_for_each_entry(mnt, &ns->list, mnt_list) {
switch (mnt->mnt.mnt_sb->s_magic) {
case SYSFS_MAGIC:
userns->may_mount_sysfs = true;
break;
case PROC_SUPER_MAGIC:
userns->may_mount_proc = true;
break;
}
if (userns->may_mount_sysfs && userns->may_mount_proc)
break;
}
up_read(&namespace_sem);
}
static void *mntns_get(struct task_struct *task)
{
struct mnt_namespace *ns = NULL;
struct nsproxy *nsproxy;
rcu_read_lock();
nsproxy = task_nsproxy(task);
if (nsproxy) {
ns = nsproxy->mnt_ns;
get_mnt_ns(ns);
}
rcu_read_unlock();
return ns;
}
static void mntns_put(void *ns)
{
put_mnt_ns(ns);
}
static int mntns_install(struct nsproxy *nsproxy, void *ns)
{
struct fs_struct *fs = current->fs;
struct mnt_namespace *mnt_ns = ns;
struct path root;
if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
!nsown_capable(CAP_SYS_CHROOT) ||
!nsown_capable(CAP_SYS_ADMIN))
return -EPERM;
if (fs->users != 1)
return -EINVAL;
get_mnt_ns(mnt_ns);
put_mnt_ns(nsproxy->mnt_ns);
nsproxy->mnt_ns = mnt_ns;
/* Find the root */
root.mnt = &mnt_ns->root->mnt;
root.dentry = mnt_ns->root->mnt.mnt_root;
path_get(&root);
while(d_mountpoint(root.dentry) && follow_down_one(&root))
;
/* Update the pwd and root */
set_fs_pwd(fs, &root);
set_fs_root(fs, &root);
path_put(&root);
return 0;
}
static unsigned int mntns_inum(void *ns)
{
struct mnt_namespace *mnt_ns = ns;
return mnt_ns->proc_inum;
}
const struct proc_ns_operations mntns_operations = {
.name = "mnt",
.type = CLONE_NEWNS,
.get = mntns_get,
.put = mntns_put,
.install = mntns_install,
.inum = mntns_inum,
};
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