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138060ba92
linux/fs/posix_acl.c
Christian Brauner 138060ba92
fs: pass dentry to set acl method 
The current way of setting and getting posix acls through the generic
xattr interface is error prone and type unsafe. The vfs needs to
interpret and fixup posix acls before storing or reporting it to
userspace. Various hacks exist to make this work. The code is hard to
understand and difficult to maintain in it's current form. Instead of
making this work by hacking posix acls through xattr handlers we are
building a dedicated posix acl api around the get and set inode
operations. This removes a lot of hackiness and makes the codepaths
easier to maintain. A lot of background can be found in [1].

Since some filesystem rely on the dentry being available to them when
setting posix acls (e.g., 9p and cifs) they cannot rely on set acl inode
operation. But since ->set_acl() is required in order to use the generic
posix acl xattr handlers filesystems that do not implement this inode
operation cannot use the handler and need to implement their own
dedicated posix acl handlers.

Update the ->set_acl() inode method to take a dentry argument. This
allows all filesystems to rely on ->set_acl().

As far as I can tell all codepaths can be switched to rely on the dentry
instead of just the inode. Note that the original motivation for passing
the dentry separate from the inode instead of just the dentry in the
xattr handlers was because of security modules that call
security_d_instantiate(). This hook is called during
d_instantiate_new(), d_add(), __d_instantiate_anon(), and
d_splice_alias() to initialize the inode's security context and possibly
to set security.* xattrs. Since this only affects security.* xattrs this
is completely irrelevant for posix acls.

Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1]
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-10-19 12:55:42 +02:00

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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2002,2003 by Andreas Gruenbacher <a.gruenbacher@computer.org>
*
* Fixes from William Schumacher incorporated on 15 March 2001.
* (Reported by Charles Bertsch, <CBertsch@microtest.com>).
*/
/*
* This file contains generic functions for manipulating
* POSIX 1003.1e draft standard 17 ACLs.
*/
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/atomic.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/cred.h>
#include <linux/posix_acl.h>
#include <linux/posix_acl_xattr.h>
#include <linux/xattr.h>
#include <linux/export.h>
#include <linux/user_namespace.h>
#include <linux/namei.h>
#include <linux/mnt_idmapping.h>
#include <linux/iversion.h>
static struct posix_acl **acl_by_type(struct inode *inode, int type)
{
switch (type) {
case ACL_TYPE_ACCESS:
return &inode->i_acl;
case ACL_TYPE_DEFAULT:
return &inode->i_default_acl;
default:
BUG();
}
}
struct posix_acl *get_cached_acl(struct inode *inode, int type)
{
struct posix_acl **p = acl_by_type(inode, type);
struct posix_acl *acl;
for (;;) {
rcu_read_lock();
acl = rcu_dereference(*p);
if (!acl || is_uncached_acl(acl) ||
refcount_inc_not_zero(&acl->a_refcount))
break;
rcu_read_unlock();
cpu_relax();
}
rcu_read_unlock();
return acl;
}
EXPORT_SYMBOL(get_cached_acl);
struct posix_acl *get_cached_acl_rcu(struct inode *inode, int type)
{
struct posix_acl *acl = rcu_dereference(*acl_by_type(inode, type));
if (acl == ACL_DONT_CACHE) {
struct posix_acl *ret;
ret = inode->i_op->get_acl(inode, type, LOOKUP_RCU);
if (!IS_ERR(ret))
acl = ret;
}
return acl;
}
EXPORT_SYMBOL(get_cached_acl_rcu);
void set_cached_acl(struct inode *inode, int type, struct posix_acl *acl)
{
struct posix_acl **p = acl_by_type(inode, type);
struct posix_acl *old;
old = xchg(p, posix_acl_dup(acl));
if (!is_uncached_acl(old))
posix_acl_release(old);
}
EXPORT_SYMBOL(set_cached_acl);
static void __forget_cached_acl(struct posix_acl **p)
{
struct posix_acl *old;
old = xchg(p, ACL_NOT_CACHED);
if (!is_uncached_acl(old))
posix_acl_release(old);
}
void forget_cached_acl(struct inode *inode, int type)
{
__forget_cached_acl(acl_by_type(inode, type));
}
EXPORT_SYMBOL(forget_cached_acl);
void forget_all_cached_acls(struct inode *inode)
{
__forget_cached_acl(&inode->i_acl);
__forget_cached_acl(&inode->i_default_acl);
}
EXPORT_SYMBOL(forget_all_cached_acls);
struct posix_acl *get_acl(struct inode *inode, int type)
{
void *sentinel;
struct posix_acl **p;
struct posix_acl *acl;
/*
* The sentinel is used to detect when another operation like
* set_cached_acl() or forget_cached_acl() races with get_acl().
* It is guaranteed that is_uncached_acl(sentinel) is true.
*/
acl = get_cached_acl(inode, type);
if (!is_uncached_acl(acl))
return acl;
if (!IS_POSIXACL(inode))
return NULL;
sentinel = uncached_acl_sentinel(current);
p = acl_by_type(inode, type);
/*
* If the ACL isn't being read yet, set our sentinel. Otherwise, the
* current value of the ACL will not be ACL_NOT_CACHED and so our own
* sentinel will not be set; another task will update the cache. We
* could wait for that other task to complete its job, but it's easier
* to just call ->get_acl to fetch the ACL ourself. (This is going to
* be an unlikely race.)
*/
cmpxchg(p, ACL_NOT_CACHED, sentinel);
/*
* Normally, the ACL returned by ->get_acl will be cached.
* A filesystem can prevent that by calling
* forget_cached_acl(inode, type) in ->get_acl.
*
* If the filesystem doesn't have a get_acl() function at all, we'll
* just create the negative cache entry.
*/
if (!inode->i_op->get_acl) {
set_cached_acl(inode, type, NULL);
return NULL;
}
acl = inode->i_op->get_acl(inode, type, false);
if (IS_ERR(acl)) {
/*
* Remove our sentinel so that we don't block future attempts
* to cache the ACL.
*/
cmpxchg(p, sentinel, ACL_NOT_CACHED);
return acl;
}
/*
* Cache the result, but only if our sentinel is still in place.
*/
posix_acl_dup(acl);
if (unlikely(cmpxchg(p, sentinel, acl) != sentinel))
posix_acl_release(acl);
return acl;
}
EXPORT_SYMBOL(get_acl);
/*
* Init a fresh posix_acl
*/
void
posix_acl_init(struct posix_acl *acl, int count)
{
refcount_set(&acl->a_refcount, 1);
acl->a_count = count;
}
EXPORT_SYMBOL(posix_acl_init);
/*
* Allocate a new ACL with the specified number of entries.
*/
struct posix_acl *
posix_acl_alloc(int count, gfp_t flags)
{
const size_t size = sizeof(struct posix_acl) +
count * sizeof(struct posix_acl_entry);
struct posix_acl *acl = kmalloc(size, flags);
if (acl)
posix_acl_init(acl, count);
return acl;
}
EXPORT_SYMBOL(posix_acl_alloc);
/*
* Clone an ACL.
*/
struct posix_acl *
posix_acl_clone(const struct posix_acl *acl, gfp_t flags)
{
struct posix_acl *clone = NULL;
if (acl) {
int size = sizeof(struct posix_acl) + acl->a_count *
sizeof(struct posix_acl_entry);
clone = kmemdup(acl, size, flags);
if (clone)
refcount_set(&clone->a_refcount, 1);
}
return clone;
}
EXPORT_SYMBOL_GPL(posix_acl_clone);
/*
* Check if an acl is valid. Returns 0 if it is, or -E... otherwise.
*/
int
posix_acl_valid(struct user_namespace *user_ns, const struct posix_acl *acl)
{
const struct posix_acl_entry *pa, *pe;
int state = ACL_USER_OBJ;
int needs_mask = 0;
FOREACH_ACL_ENTRY(pa, acl, pe) {
if (pa->e_perm & ~(ACL_READ|ACL_WRITE|ACL_EXECUTE))
return -EINVAL;
switch (pa->e_tag) {
case ACL_USER_OBJ:
if (state == ACL_USER_OBJ) {
state = ACL_USER;
break;
}
return -EINVAL;
case ACL_USER:
if (state != ACL_USER)
return -EINVAL;
if (!kuid_has_mapping(user_ns, pa->e_uid))
return -EINVAL;
needs_mask = 1;
break;
case ACL_GROUP_OBJ:
if (state == ACL_USER) {
state = ACL_GROUP;
break;
}
return -EINVAL;
case ACL_GROUP:
if (state != ACL_GROUP)
return -EINVAL;
if (!kgid_has_mapping(user_ns, pa->e_gid))
return -EINVAL;
needs_mask = 1;
break;
case ACL_MASK:
if (state != ACL_GROUP)
return -EINVAL;
state = ACL_OTHER;
break;
case ACL_OTHER:
if (state == ACL_OTHER ||
(state == ACL_GROUP && !needs_mask)) {
state = 0;
break;
}
return -EINVAL;
default:
return -EINVAL;
}
}
if (state == 0)
return 0;
return -EINVAL;
}
EXPORT_SYMBOL(posix_acl_valid);
/*
* Returns 0 if the acl can be exactly represented in the traditional
* file mode permission bits, or else 1. Returns -E... on error.
*/
int
posix_acl_equiv_mode(const struct posix_acl *acl, umode_t *mode_p)
{
const struct posix_acl_entry *pa, *pe;
umode_t mode = 0;
int not_equiv = 0;
/*
* A null ACL can always be presented as mode bits.
*/
if (!acl)
return 0;
FOREACH_ACL_ENTRY(pa, acl, pe) {
switch (pa->e_tag) {
case ACL_USER_OBJ:
mode |= (pa->e_perm & S_IRWXO) << 6;
break;
case ACL_GROUP_OBJ:
mode |= (pa->e_perm & S_IRWXO) << 3;
break;
case ACL_OTHER:
mode |= pa->e_perm & S_IRWXO;
break;
case ACL_MASK:
mode = (mode & ~S_IRWXG) |
((pa->e_perm & S_IRWXO) << 3);
not_equiv = 1;
break;
case ACL_USER:
case ACL_GROUP:
not_equiv = 1;
break;
default:
return -EINVAL;
}
}
if (mode_p)
*mode_p = (*mode_p & ~S_IRWXUGO) | mode;
return not_equiv;
}
EXPORT_SYMBOL(posix_acl_equiv_mode);
/*
* Create an ACL representing the file mode permission bits of an inode.
*/
struct posix_acl *
posix_acl_from_mode(umode_t mode, gfp_t flags)
{
struct posix_acl *acl = posix_acl_alloc(3, flags);
if (!acl)
return ERR_PTR(-ENOMEM);
acl->a_entries[0].e_tag = ACL_USER_OBJ;
acl->a_entries[0].e_perm = (mode & S_IRWXU) >> 6;
acl->a_entries[1].e_tag = ACL_GROUP_OBJ;
acl->a_entries[1].e_perm = (mode & S_IRWXG) >> 3;
acl->a_entries[2].e_tag = ACL_OTHER;
acl->a_entries[2].e_perm = (mode & S_IRWXO);
return acl;
}
EXPORT_SYMBOL(posix_acl_from_mode);
/*
* Return 0 if current is granted want access to the inode
* by the acl. Returns -E... otherwise.
*/
int
posix_acl_permission(struct user_namespace *mnt_userns, struct inode *inode,
const struct posix_acl *acl, int want)
{
const struct posix_acl_entry *pa, *pe, *mask_obj;
struct user_namespace *fs_userns = i_user_ns(inode);
int found = 0;
vfsuid_t vfsuid;
vfsgid_t vfsgid;
want &= MAY_READ | MAY_WRITE | MAY_EXEC;
FOREACH_ACL_ENTRY(pa, acl, pe) {
switch(pa->e_tag) {
case ACL_USER_OBJ:
/* (May have been checked already) */
vfsuid = i_uid_into_vfsuid(mnt_userns, inode);
if (vfsuid_eq_kuid(vfsuid, current_fsuid()))
goto check_perm;
break;
case ACL_USER:
vfsuid = make_vfsuid(mnt_userns, fs_userns,
pa->e_uid);
if (vfsuid_eq_kuid(vfsuid, current_fsuid()))
goto mask;
break;
case ACL_GROUP_OBJ:
vfsgid = i_gid_into_vfsgid(mnt_userns, inode);
if (vfsgid_in_group_p(vfsgid)) {
found = 1;
if ((pa->e_perm & want) == want)
goto mask;
}
break;
case ACL_GROUP:
vfsgid = make_vfsgid(mnt_userns, fs_userns,
pa->e_gid);
if (vfsgid_in_group_p(vfsgid)) {
found = 1;
if ((pa->e_perm & want) == want)
goto mask;
}
break;
case ACL_MASK:
break;
case ACL_OTHER:
if (found)
return -EACCES;
else
goto check_perm;
default:
return -EIO;
}
}
return -EIO;
mask:
for (mask_obj = pa+1; mask_obj != pe; mask_obj++) {
if (mask_obj->e_tag == ACL_MASK) {
if ((pa->e_perm & mask_obj->e_perm & want) == want)
return 0;
return -EACCES;
}
}
check_perm:
if ((pa->e_perm & want) == want)
return 0;
return -EACCES;
}
/*
* Modify acl when creating a new inode. The caller must ensure the acl is
* only referenced once.
*
* mode_p initially must contain the mode parameter to the open() / creat()
* system calls. All permissions that are not granted by the acl are removed.
* The permissions in the acl are changed to reflect the mode_p parameter.
*/
static int posix_acl_create_masq(struct posix_acl *acl, umode_t *mode_p)
{
struct posix_acl_entry *pa, *pe;
struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
umode_t mode = *mode_p;
int not_equiv = 0;
/* assert(atomic_read(acl->a_refcount) == 1); */
FOREACH_ACL_ENTRY(pa, acl, pe) {
switch(pa->e_tag) {
case ACL_USER_OBJ:
pa->e_perm &= (mode >> 6) | ~S_IRWXO;
mode &= (pa->e_perm << 6) | ~S_IRWXU;
break;
case ACL_USER:
case ACL_GROUP:
not_equiv = 1;
break;
case ACL_GROUP_OBJ:
group_obj = pa;
break;
case ACL_OTHER:
pa->e_perm &= mode | ~S_IRWXO;
mode &= pa->e_perm | ~S_IRWXO;
break;
case ACL_MASK:
mask_obj = pa;
not_equiv = 1;
break;
default:
return -EIO;
}
}
if (mask_obj) {
mask_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
mode &= (mask_obj->e_perm << 3) | ~S_IRWXG;
} else {
if (!group_obj)
return -EIO;
group_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
mode &= (group_obj->e_perm << 3) | ~S_IRWXG;
}
*mode_p = (*mode_p & ~S_IRWXUGO) | mode;
return not_equiv;
}
/*
* Modify the ACL for the chmod syscall.
*/
static int __posix_acl_chmod_masq(struct posix_acl *acl, umode_t mode)
{
struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
struct posix_acl_entry *pa, *pe;
/* assert(atomic_read(acl->a_refcount) == 1); */
FOREACH_ACL_ENTRY(pa, acl, pe) {
switch(pa->e_tag) {
case ACL_USER_OBJ:
pa->e_perm = (mode & S_IRWXU) >> 6;
break;
case ACL_USER:
case ACL_GROUP:
break;
case ACL_GROUP_OBJ:
group_obj = pa;
break;
case ACL_MASK:
mask_obj = pa;
break;
case ACL_OTHER:
pa->e_perm = (mode & S_IRWXO);
break;
default:
return -EIO;
}
}
if (mask_obj) {
mask_obj->e_perm = (mode & S_IRWXG) >> 3;
} else {
if (!group_obj)
return -EIO;
group_obj->e_perm = (mode & S_IRWXG) >> 3;
}
return 0;
}
int
__posix_acl_create(struct posix_acl **acl, gfp_t gfp, umode_t *mode_p)
{
struct posix_acl *clone = posix_acl_clone(*acl, gfp);
int err = -ENOMEM;
if (clone) {
err = posix_acl_create_masq(clone, mode_p);
if (err < 0) {
posix_acl_release(clone);
clone = NULL;
}
}
posix_acl_release(*acl);
*acl = clone;
return err;
}
EXPORT_SYMBOL(__posix_acl_create);
int
__posix_acl_chmod(struct posix_acl **acl, gfp_t gfp, umode_t mode)
{
struct posix_acl *clone = posix_acl_clone(*acl, gfp);
int err = -ENOMEM;
if (clone) {
err = __posix_acl_chmod_masq(clone, mode);
if (err) {
posix_acl_release(clone);
clone = NULL;
}
}
posix_acl_release(*acl);
*acl = clone;
return err;
}
EXPORT_SYMBOL(__posix_acl_chmod);
/**
* posix_acl_chmod - chmod a posix acl
*
* @mnt_userns: user namespace of the mount @inode was found from
* @dentry: dentry to check permissions on
* @mode: the new mode of @inode
*
* If the dentry has been found through an idmapped mount the user namespace of
* the vfsmount must be passed through @mnt_userns. This function will then
* take care to map the inode according to @mnt_userns before checking
* permissions. On non-idmapped mounts or if permission checking is to be
* performed on the raw inode simply passs init_user_ns.
*/
int
posix_acl_chmod(struct user_namespace *mnt_userns, struct dentry *dentry,
umode_t mode)
{
struct inode *inode = d_inode(dentry);
struct posix_acl *acl;
int ret = 0;
if (!IS_POSIXACL(inode))
return 0;
if (!inode->i_op->set_acl)
return -EOPNOTSUPP;
acl = get_acl(inode, ACL_TYPE_ACCESS);
if (IS_ERR_OR_NULL(acl)) {
if (acl == ERR_PTR(-EOPNOTSUPP))
return 0;
return PTR_ERR(acl);
}
ret = __posix_acl_chmod(&acl, GFP_KERNEL, mode);
if (ret)
return ret;
ret = inode->i_op->set_acl(mnt_userns, dentry, acl, ACL_TYPE_ACCESS);
posix_acl_release(acl);
return ret;
}
EXPORT_SYMBOL(posix_acl_chmod);
int
posix_acl_create(struct inode *dir, umode_t *mode,
struct posix_acl **default_acl, struct posix_acl **acl)
{
struct posix_acl *p;
struct posix_acl *clone;
int ret;
*acl = NULL;
*default_acl = NULL;
if (S_ISLNK(*mode) || !IS_POSIXACL(dir))
return 0;
p = get_acl(dir, ACL_TYPE_DEFAULT);
if (!p || p == ERR_PTR(-EOPNOTSUPP)) {
*mode &= ~current_umask();
return 0;
}
if (IS_ERR(p))
return PTR_ERR(p);
ret = -ENOMEM;
clone = posix_acl_clone(p, GFP_NOFS);
if (!clone)
goto err_release;
ret = posix_acl_create_masq(clone, mode);
if (ret < 0)
goto err_release_clone;
if (ret == 0)
posix_acl_release(clone);
else
*acl = clone;
if (!S_ISDIR(*mode))
posix_acl_release(p);
else
*default_acl = p;
return 0;
err_release_clone:
posix_acl_release(clone);
err_release:
posix_acl_release(p);
return ret;
}
EXPORT_SYMBOL_GPL(posix_acl_create);
/**
* posix_acl_update_mode - update mode in set_acl
* @mnt_userns: user namespace of the mount @inode was found from
* @inode: target inode
* @mode_p: mode (pointer) for update
* @acl: acl pointer
*
* Update the file mode when setting an ACL: compute the new file permission
* bits based on the ACL. In addition, if the ACL is equivalent to the new
* file mode, set *@acl to NULL to indicate that no ACL should be set.
*
* As with chmod, clear the setgid bit if the caller is not in the owning group
* or capable of CAP_FSETID (see inode_change_ok).
*
* If the inode has been found through an idmapped mount the user namespace of
* the vfsmount must be passed through @mnt_userns. This function will then
* take care to map the inode according to @mnt_userns before checking
* permissions. On non-idmapped mounts or if permission checking is to be
* performed on the raw inode simply passs init_user_ns.
*
* Called from set_acl inode operations.
*/
int posix_acl_update_mode(struct user_namespace *mnt_userns,
struct inode *inode, umode_t *mode_p,
struct posix_acl **acl)
{
umode_t mode = inode->i_mode;
int error;
error = posix_acl_equiv_mode(*acl, &mode);
if (error < 0)
return error;
if (error == 0)
*acl = NULL;
if (!vfsgid_in_group_p(i_gid_into_vfsgid(mnt_userns, inode)) &&
!capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
mode &= ~S_ISGID;
*mode_p = mode;
return 0;
}
EXPORT_SYMBOL(posix_acl_update_mode);
/*
* Fix up the uids and gids in posix acl extended attributes in place.
*/
static int posix_acl_fix_xattr_common(const void *value, size_t size)
{
const struct posix_acl_xattr_header *header = value;
int count;
if (!header)
return -EINVAL;
if (size < sizeof(struct posix_acl_xattr_header))
return -EINVAL;
if (header->a_version != cpu_to_le32(POSIX_ACL_XATTR_VERSION))
return -EOPNOTSUPP;
count = posix_acl_xattr_count(size);
if (count < 0)
return -EINVAL;
if (count == 0)
return 0;
return count;
}
void posix_acl_getxattr_idmapped_mnt(struct user_namespace *mnt_userns,
const struct inode *inode,
void *value, size_t size)
{
struct posix_acl_xattr_header *header = value;
struct posix_acl_xattr_entry *entry = (void *)(header + 1), *end;
struct user_namespace *fs_userns = i_user_ns(inode);
int count;
vfsuid_t vfsuid;
vfsgid_t vfsgid;
kuid_t uid;
kgid_t gid;
if (no_idmapping(mnt_userns, i_user_ns(inode)))
return;
count = posix_acl_fix_xattr_common(value, size);
if (count <= 0)
return;
for (end = entry + count; entry != end; entry++) {
switch (le16_to_cpu(entry->e_tag)) {
case ACL_USER:
uid = make_kuid(&init_user_ns, le32_to_cpu(entry->e_id));
vfsuid = make_vfsuid(mnt_userns, fs_userns, uid);
entry->e_id = cpu_to_le32(from_kuid(&init_user_ns,
vfsuid_into_kuid(vfsuid)));
break;
case ACL_GROUP:
gid = make_kgid(&init_user_ns, le32_to_cpu(entry->e_id));
vfsgid = make_vfsgid(mnt_userns, fs_userns, gid);
entry->e_id = cpu_to_le32(from_kgid(&init_user_ns,
vfsgid_into_kgid(vfsgid)));
break;
default:
break;
}
}
}
static void posix_acl_fix_xattr_userns(
struct user_namespace *to, struct user_namespace *from,
void *value, size_t size)
{
struct posix_acl_xattr_header *header = value;
struct posix_acl_xattr_entry *entry = (void *)(header + 1), *end;
int count;
kuid_t uid;
kgid_t gid;
count = posix_acl_fix_xattr_common(value, size);
if (count <= 0)
return;
for (end = entry + count; entry != end; entry++) {
switch(le16_to_cpu(entry->e_tag)) {
case ACL_USER:
uid = make_kuid(from, le32_to_cpu(entry->e_id));
entry->e_id = cpu_to_le32(from_kuid(to, uid));
break;
case ACL_GROUP:
gid = make_kgid(from, le32_to_cpu(entry->e_id));
entry->e_id = cpu_to_le32(from_kgid(to, gid));
break;
default:
break;
}
}
}
void posix_acl_fix_xattr_from_user(void *value, size_t size)
{
struct user_namespace *user_ns = current_user_ns();
if (user_ns == &init_user_ns)
return;
posix_acl_fix_xattr_userns(&init_user_ns, user_ns, value, size);
}
void posix_acl_fix_xattr_to_user(void *value, size_t size)
{
struct user_namespace *user_ns = current_user_ns();
if (user_ns == &init_user_ns)
return;
posix_acl_fix_xattr_userns(user_ns, &init_user_ns, value, size);
}
/**
* make_posix_acl - convert POSIX ACLs from uapi to VFS format using the
* provided callbacks to map ACL_{GROUP,USER} entries into the
* appropriate format
* @mnt_userns: the mount's idmapping
* @fs_userns: the filesystem's idmapping
* @value: the uapi representation of POSIX ACLs
* @size: the size of @void
* @uid_cb: callback to use for mapping the uid stored in ACL_USER entries
* @gid_cb: callback to use for mapping the gid stored in ACL_GROUP entries
*
* The make_posix_acl() helper is an abstraction to translate from uapi format
* into the VFS format allowing the caller to specific callbacks to map
* ACL_{GROUP,USER} entries into the expected format. This is used in
* posix_acl_from_xattr() and vfs_set_acl_prepare() and avoids pointless code
* duplication.
*
* Return: Allocated struct posix_acl on success, NULL for a valid header but
* without actual POSIX ACL entries, or ERR_PTR() encoded error code.
*/
static struct posix_acl *make_posix_acl(struct user_namespace *mnt_userns,
struct user_namespace *fs_userns, const void *value, size_t size,
kuid_t (*uid_cb)(struct user_namespace *, struct user_namespace *,
const struct posix_acl_xattr_entry *),
kgid_t (*gid_cb)(struct user_namespace *, struct user_namespace *,
const struct posix_acl_xattr_entry *))
{
const struct posix_acl_xattr_header *header = value;
const struct posix_acl_xattr_entry *entry = (const void *)(header + 1), *end;
int count;
struct posix_acl *acl;
struct posix_acl_entry *acl_e;
count = posix_acl_fix_xattr_common(value, size);
if (count < 0)
return ERR_PTR(count);
if (count == 0)
return NULL;
acl = posix_acl_alloc(count, GFP_NOFS);
if (!acl)
return ERR_PTR(-ENOMEM);
acl_e = acl->a_entries;
for (end = entry + count; entry != end; acl_e++, entry++) {
acl_e->e_tag = le16_to_cpu(entry->e_tag);
acl_e->e_perm = le16_to_cpu(entry->e_perm);
switch(acl_e->e_tag) {
case ACL_USER_OBJ:
case ACL_GROUP_OBJ:
case ACL_MASK:
case ACL_OTHER:
break;
case ACL_USER:
acl_e->e_uid = uid_cb(mnt_userns, fs_userns, entry);
if (!uid_valid(acl_e->e_uid))
goto fail;
break;
case ACL_GROUP:
acl_e->e_gid = gid_cb(mnt_userns, fs_userns, entry);
if (!gid_valid(acl_e->e_gid))
goto fail;
break;
default:
goto fail;
}
}
return acl;
fail:
posix_acl_release(acl);
return ERR_PTR(-EINVAL);
}
/**
* vfs_set_acl_prepare_kuid - map ACL_USER uid according to mount- and
* filesystem idmapping
* @mnt_userns: the mount's idmapping
* @fs_userns: the filesystem's idmapping
* @e: a ACL_USER entry in POSIX ACL uapi format
*
* The uid stored as ACL_USER entry in @e is a kuid_t stored as a raw {g,u}id
* value. The vfs_set_acl_prepare_kuid() will recover the kuid_t through
* KUIDT_INIT() and then map it according to the idmapped mount. The resulting
* kuid_t is the value which the filesystem can map up into a raw backing store
* id in the filesystem's idmapping.
*
* This is used in vfs_set_acl_prepare() to generate the proper VFS
* representation of POSIX ACLs with ACL_USER entries during setxattr().
*
* Return: A kuid in @fs_userns for the uid stored in @e.
*/
static inline kuid_t
vfs_set_acl_prepare_kuid(struct user_namespace *mnt_userns,
struct user_namespace *fs_userns,
const struct posix_acl_xattr_entry *e)
{
kuid_t kuid = KUIDT_INIT(le32_to_cpu(e->e_id));
return from_vfsuid(mnt_userns, fs_userns, VFSUIDT_INIT(kuid));
}
/**
* vfs_set_acl_prepare_kgid - map ACL_GROUP gid according to mount- and
* filesystem idmapping
* @mnt_userns: the mount's idmapping
* @fs_userns: the filesystem's idmapping
* @e: a ACL_GROUP entry in POSIX ACL uapi format
*
* The gid stored as ACL_GROUP entry in @e is a kgid_t stored as a raw {g,u}id
* value. The vfs_set_acl_prepare_kgid() will recover the kgid_t through
* KGIDT_INIT() and then map it according to the idmapped mount. The resulting
* kgid_t is the value which the filesystem can map up into a raw backing store
* id in the filesystem's idmapping.
*
* This is used in vfs_set_acl_prepare() to generate the proper VFS
* representation of POSIX ACLs with ACL_GROUP entries during setxattr().
*
* Return: A kgid in @fs_userns for the gid stored in @e.
*/
static inline kgid_t
vfs_set_acl_prepare_kgid(struct user_namespace *mnt_userns,
struct user_namespace *fs_userns,
const struct posix_acl_xattr_entry *e)
{
kgid_t kgid = KGIDT_INIT(le32_to_cpu(e->e_id));
return from_vfsgid(mnt_userns, fs_userns, VFSGIDT_INIT(kgid));
}
/**
* vfs_set_acl_prepare - convert POSIX ACLs from uapi to VFS format taking
* mount and filesystem idmappings into account
* @mnt_userns: the mount's idmapping
* @fs_userns: the filesystem's idmapping
* @value: the uapi representation of POSIX ACLs
* @size: the size of @void
*
* When setting POSIX ACLs with ACL_{GROUP,USER} entries they need to be
* mapped according to the relevant mount- and filesystem idmapping. It is
* important that the ACL_{GROUP,USER} entries in struct posix_acl will be
* mapped into k{g,u}id_t that are supposed to be mapped up in the filesystem
* idmapping. This is crucial since the resulting struct posix_acl might be
* cached filesystem wide. The vfs_set_acl_prepare() function will take care to
* perform all necessary idmappings.
*
* Note, that since basically forever the {g,u}id values encoded as
* ACL_{GROUP,USER} entries in the uapi POSIX ACLs passed via @value contain
* values that have been mapped according to the caller's idmapping. In other
* words, POSIX ACLs passed in uapi format as @value during setxattr() contain
* {g,u}id values in their ACL_{GROUP,USER} entries that should actually have
* been stored as k{g,u}id_t.
*
* This means, vfs_set_acl_prepare() needs to first recover the k{g,u}id_t by
* calling K{G,U}IDT_INIT(). Afterwards they can be interpreted as vfs{g,u}id_t
* through from_vfs{g,u}id() to account for any idmapped mounts. The
* vfs_set_acl_prepare_k{g,u}id() helpers will take care to generate the
* correct k{g,u}id_t.
*
* The filesystem will then receive the POSIX ACLs ready to be cached
* filesystem wide and ready to be written to the backing store taking the
* filesystem's idmapping into account.
*
* Return: Allocated struct posix_acl on success, NULL for a valid header but
* without actual POSIX ACL entries, or ERR_PTR() encoded error code.
*/
struct posix_acl *vfs_set_acl_prepare(struct user_namespace *mnt_userns,
struct user_namespace *fs_userns,
const void *value, size_t size)
{
return make_posix_acl(mnt_userns, fs_userns, value, size,
vfs_set_acl_prepare_kuid,
vfs_set_acl_prepare_kgid);
}
EXPORT_SYMBOL(vfs_set_acl_prepare);
/**
* posix_acl_from_xattr_kuid - map ACL_USER uid into filesystem idmapping
* @mnt_userns: unused
* @fs_userns: the filesystem's idmapping
* @e: a ACL_USER entry in POSIX ACL uapi format
*
* Map the uid stored as ACL_USER entry in @e into the filesystem's idmapping.
* This is used in posix_acl_from_xattr() to generate the proper VFS
* representation of POSIX ACLs with ACL_USER entries.
*
* Return: A kuid in @fs_userns for the uid stored in @e.
*/
static inline kuid_t
posix_acl_from_xattr_kuid(struct user_namespace *mnt_userns,
struct user_namespace *fs_userns,
const struct posix_acl_xattr_entry *e)
{
return make_kuid(fs_userns, le32_to_cpu(e->e_id));
}
/**
* posix_acl_from_xattr_kgid - map ACL_GROUP gid into filesystem idmapping
* @mnt_userns: unused
* @fs_userns: the filesystem's idmapping
* @e: a ACL_GROUP entry in POSIX ACL uapi format
*
* Map the gid stored as ACL_GROUP entry in @e into the filesystem's idmapping.
* This is used in posix_acl_from_xattr() to generate the proper VFS
* representation of POSIX ACLs with ACL_GROUP entries.
*
* Return: A kgid in @fs_userns for the gid stored in @e.
*/
static inline kgid_t
posix_acl_from_xattr_kgid(struct user_namespace *mnt_userns,
struct user_namespace *fs_userns,
const struct posix_acl_xattr_entry *e)
{
return make_kgid(fs_userns, le32_to_cpu(e->e_id));
}
/**
* posix_acl_from_xattr - convert POSIX ACLs from backing store to VFS format
* @fs_userns: the filesystem's idmapping
* @value: the uapi representation of POSIX ACLs
* @size: the size of @void
*
* Filesystems that store POSIX ACLs in the unaltered uapi format should use
* posix_acl_from_xattr() when reading them from the backing store and
* converting them into the struct posix_acl VFS format. The helper is
* specifically intended to be called from the ->get_acl() inode operation.
*
* The posix_acl_from_xattr() function will map the raw {g,u}id values stored
* in ACL_{GROUP,USER} entries into the filesystem idmapping in @fs_userns. The
* posix_acl_from_xattr_k{g,u}id() helpers will take care to generate the
* correct k{g,u}id_t. The returned struct posix_acl can be cached.
*
* Note that posix_acl_from_xattr() does not take idmapped mounts into account.
* If it did it calling is from the ->get_acl() inode operation would return
* POSIX ACLs mapped according to an idmapped mount which would mean that the
* value couldn't be cached for the filesystem. Idmapped mounts are taken into
* account on the fly during permission checking or right at the VFS -
* userspace boundary before reporting them to the user.
*
* Return: Allocated struct posix_acl on success, NULL for a valid header but
* without actual POSIX ACL entries, or ERR_PTR() encoded error code.
*/
struct posix_acl *
posix_acl_from_xattr(struct user_namespace *fs_userns,
const void *value, size_t size)
{
return make_posix_acl(&init_user_ns, fs_userns, value, size,
posix_acl_from_xattr_kuid,
posix_acl_from_xattr_kgid);
}
EXPORT_SYMBOL (posix_acl_from_xattr);
/*
* Convert from in-memory to extended attribute representation.
*/
int
posix_acl_to_xattr(struct user_namespace *user_ns, const struct posix_acl *acl,
void *buffer, size_t size)
{
struct posix_acl_xattr_header *ext_acl = buffer;
struct posix_acl_xattr_entry *ext_entry;
int real_size, n;
real_size = posix_acl_xattr_size(acl->a_count);
if (!buffer)
return real_size;
if (real_size > size)
return -ERANGE;
ext_entry = (void *)(ext_acl + 1);
ext_acl->a_version = cpu_to_le32(POSIX_ACL_XATTR_VERSION);
for (n=0; n < acl->a_count; n++, ext_entry++) {
const struct posix_acl_entry *acl_e = &acl->a_entries[n];
ext_entry->e_tag = cpu_to_le16(acl_e->e_tag);
ext_entry->e_perm = cpu_to_le16(acl_e->e_perm);
switch(acl_e->e_tag) {
case ACL_USER:
ext_entry->e_id =
cpu_to_le32(from_kuid(user_ns, acl_e->e_uid));
break;
case ACL_GROUP:
ext_entry->e_id =
cpu_to_le32(from_kgid(user_ns, acl_e->e_gid));
break;
default:
ext_entry->e_id = cpu_to_le32(ACL_UNDEFINED_ID);
break;
}
}
return real_size;
}
EXPORT_SYMBOL (posix_acl_to_xattr);
static int
posix_acl_xattr_get(const struct xattr_handler *handler,
struct dentry *unused, struct inode *inode,
const char *name, void *value, size_t size)
{
struct posix_acl *acl;
int error;
if (!IS_POSIXACL(inode))
return -EOPNOTSUPP;
if (S_ISLNK(inode->i_mode))
return -EOPNOTSUPP;
acl = get_acl(inode, handler->flags);
if (IS_ERR(acl))
return PTR_ERR(acl);
if (acl == NULL)
return -ENODATA;
error = posix_acl_to_xattr(&init_user_ns, acl, value, size);
posix_acl_release(acl);
return error;
}
int
set_posix_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
int type, struct posix_acl *acl)
{
struct inode *inode = d_inode(dentry);
if (!IS_POSIXACL(inode))
return -EOPNOTSUPP;
if (!inode->i_op->set_acl)
return -EOPNOTSUPP;
if (type == ACL_TYPE_DEFAULT && !S_ISDIR(inode->i_mode))
return acl ? -EACCES : 0;
if (!inode_owner_or_capable(mnt_userns, inode))
return -EPERM;
if (acl) {
int ret = posix_acl_valid(inode->i_sb->s_user_ns, acl);
if (ret)
return ret;
}
return inode->i_op->set_acl(mnt_userns, dentry, acl, type);
}
EXPORT_SYMBOL(set_posix_acl);
static int
posix_acl_xattr_set(const struct xattr_handler *handler,
struct user_namespace *mnt_userns,
struct dentry *dentry, struct inode *inode,
const char *name, const void *value, size_t size,
int flags)
{
struct posix_acl *acl = NULL;
int ret;
if (value) {
/*
* By the time we end up here the {g,u}ids stored in
* ACL_{GROUP,USER} have already been mapped according to the
* caller's idmapping. The vfs_set_acl_prepare() helper will
* recover them and take idmapped mounts into account. The
* filesystem will receive the POSIX ACLs in the correct
* format ready to be cached or written to the backing store
* taking the filesystem idmapping into account.
*/
acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode),
value, size);
if (IS_ERR(acl))
return PTR_ERR(acl);
}
ret = set_posix_acl(mnt_userns, dentry, handler->flags, acl);
posix_acl_release(acl);
return ret;
}
static bool
posix_acl_xattr_list(struct dentry *dentry)
{
return IS_POSIXACL(d_backing_inode(dentry));
}
const struct xattr_handler posix_acl_access_xattr_handler = {
.name = XATTR_NAME_POSIX_ACL_ACCESS,
.flags = ACL_TYPE_ACCESS,
.list = posix_acl_xattr_list,
.get = posix_acl_xattr_get,
.set = posix_acl_xattr_set,
};
EXPORT_SYMBOL_GPL(posix_acl_access_xattr_handler);
const struct xattr_handler posix_acl_default_xattr_handler = {
.name = XATTR_NAME_POSIX_ACL_DEFAULT,
.flags = ACL_TYPE_DEFAULT,
.list = posix_acl_xattr_list,
.get = posix_acl_xattr_get,
.set = posix_acl_xattr_set,
};
EXPORT_SYMBOL_GPL(posix_acl_default_xattr_handler);
int simple_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
struct posix_acl *acl, int type)
{
int error;
struct inode *inode = d_inode(dentry);
if (type == ACL_TYPE_ACCESS) {
error = posix_acl_update_mode(mnt_userns, inode,
&inode->i_mode, &acl);
if (error)
return error;
}
inode->i_ctime = current_time(inode);
if (IS_I_VERSION(inode))
inode_inc_iversion(inode);
set_cached_acl(inode, type, acl);
return 0;
}
int simple_acl_create(struct inode *dir, struct inode *inode)
{
struct posix_acl *default_acl, *acl;
int error;
error = posix_acl_create(dir, &inode->i_mode, &default_acl, &acl);
if (error)
return error;
set_cached_acl(inode, ACL_TYPE_DEFAULT, default_acl);
set_cached_acl(inode, ACL_TYPE_ACCESS, acl);
if (default_acl)
posix_acl_release(default_acl);
if (acl)
posix_acl_release(acl);
return 0;
}
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