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0c47383ba3
User extended attributes are useful as metadata storage for kernfs consumers like cgroups. Especially in the case of cgroups, it is useful to have a central metadata store that multiple processes/services can use to coordinate actions. A concrete example is for userspace out of memory killers. We want to let delegated cgroup subtree owners (running as non-root) to be able to say "please avoid killing this cgroup". This is especially important for desktop linux as delegated subtrees owners are less likely to run as root. This patch introduces a new flag, KERNFS_ROOT_SUPPORT_USER_XATTR, that lets kernfs consumers enable user xattr support. An initial limit of 128 entries or 128KB -- whichever is hit first -- is placed per cgroup because xattrs come from kernel memory and we don't want to let unprivileged users accidentally eat up too much kernel memory. Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> Acked-by: Chris Down <chris@chrisdown.name> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Tejun Heo <tj@kernel.org>
436 lines
10 KiB
C
436 lines
10 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* fs/kernfs/inode.c - kernfs inode implementation
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*
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* Copyright (c) 2001-3 Patrick Mochel
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* Copyright (c) 2007 SUSE Linux Products GmbH
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* Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
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*/
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#include <linux/pagemap.h>
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#include <linux/backing-dev.h>
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#include <linux/capability.h>
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#include <linux/errno.h>
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#include <linux/slab.h>
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#include <linux/xattr.h>
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#include <linux/security.h>
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#include "kernfs-internal.h"
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static const struct address_space_operations kernfs_aops = {
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.readpage = simple_readpage,
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.write_begin = simple_write_begin,
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.write_end = simple_write_end,
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};
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static const struct inode_operations kernfs_iops = {
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.permission = kernfs_iop_permission,
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.setattr = kernfs_iop_setattr,
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.getattr = kernfs_iop_getattr,
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.listxattr = kernfs_iop_listxattr,
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};
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static struct kernfs_iattrs *__kernfs_iattrs(struct kernfs_node *kn, int alloc)
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{
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static DEFINE_MUTEX(iattr_mutex);
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struct kernfs_iattrs *ret;
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mutex_lock(&iattr_mutex);
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if (kn->iattr || !alloc)
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goto out_unlock;
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kn->iattr = kmem_cache_zalloc(kernfs_iattrs_cache, GFP_KERNEL);
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if (!kn->iattr)
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goto out_unlock;
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/* assign default attributes */
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kn->iattr->ia_uid = GLOBAL_ROOT_UID;
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kn->iattr->ia_gid = GLOBAL_ROOT_GID;
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ktime_get_real_ts64(&kn->iattr->ia_atime);
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kn->iattr->ia_mtime = kn->iattr->ia_atime;
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kn->iattr->ia_ctime = kn->iattr->ia_atime;
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simple_xattrs_init(&kn->iattr->xattrs);
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atomic_set(&kn->iattr->nr_user_xattrs, 0);
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atomic_set(&kn->iattr->user_xattr_size, 0);
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out_unlock:
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ret = kn->iattr;
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mutex_unlock(&iattr_mutex);
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return ret;
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}
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static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
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{
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return __kernfs_iattrs(kn, 1);
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}
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static struct kernfs_iattrs *kernfs_iattrs_noalloc(struct kernfs_node *kn)
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{
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return __kernfs_iattrs(kn, 0);
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}
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int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
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{
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struct kernfs_iattrs *attrs;
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unsigned int ia_valid = iattr->ia_valid;
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attrs = kernfs_iattrs(kn);
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if (!attrs)
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return -ENOMEM;
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if (ia_valid & ATTR_UID)
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attrs->ia_uid = iattr->ia_uid;
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if (ia_valid & ATTR_GID)
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attrs->ia_gid = iattr->ia_gid;
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if (ia_valid & ATTR_ATIME)
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attrs->ia_atime = iattr->ia_atime;
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if (ia_valid & ATTR_MTIME)
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attrs->ia_mtime = iattr->ia_mtime;
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if (ia_valid & ATTR_CTIME)
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attrs->ia_ctime = iattr->ia_ctime;
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if (ia_valid & ATTR_MODE)
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kn->mode = iattr->ia_mode;
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return 0;
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}
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/**
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* kernfs_setattr - set iattr on a node
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* @kn: target node
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* @iattr: iattr to set
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*
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* Returns 0 on success, -errno on failure.
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*/
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int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
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{
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int ret;
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mutex_lock(&kernfs_mutex);
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ret = __kernfs_setattr(kn, iattr);
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mutex_unlock(&kernfs_mutex);
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return ret;
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}
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int kernfs_iop_setattr(struct dentry *dentry, struct iattr *iattr)
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{
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struct inode *inode = d_inode(dentry);
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struct kernfs_node *kn = inode->i_private;
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int error;
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if (!kn)
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return -EINVAL;
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mutex_lock(&kernfs_mutex);
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error = setattr_prepare(dentry, iattr);
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if (error)
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goto out;
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error = __kernfs_setattr(kn, iattr);
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if (error)
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goto out;
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/* this ignores size changes */
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setattr_copy(inode, iattr);
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out:
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mutex_unlock(&kernfs_mutex);
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return error;
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}
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ssize_t kernfs_iop_listxattr(struct dentry *dentry, char *buf, size_t size)
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{
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struct kernfs_node *kn = kernfs_dentry_node(dentry);
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struct kernfs_iattrs *attrs;
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attrs = kernfs_iattrs(kn);
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if (!attrs)
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return -ENOMEM;
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return simple_xattr_list(d_inode(dentry), &attrs->xattrs, buf, size);
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}
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static inline void set_default_inode_attr(struct inode *inode, umode_t mode)
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{
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inode->i_mode = mode;
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inode->i_atime = inode->i_mtime =
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inode->i_ctime = current_time(inode);
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}
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static inline void set_inode_attr(struct inode *inode,
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struct kernfs_iattrs *attrs)
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{
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inode->i_uid = attrs->ia_uid;
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inode->i_gid = attrs->ia_gid;
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inode->i_atime = attrs->ia_atime;
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inode->i_mtime = attrs->ia_mtime;
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inode->i_ctime = attrs->ia_ctime;
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}
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static void kernfs_refresh_inode(struct kernfs_node *kn, struct inode *inode)
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{
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struct kernfs_iattrs *attrs = kn->iattr;
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inode->i_mode = kn->mode;
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if (attrs)
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/*
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* kernfs_node has non-default attributes get them from
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* persistent copy in kernfs_node.
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*/
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set_inode_attr(inode, attrs);
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if (kernfs_type(kn) == KERNFS_DIR)
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set_nlink(inode, kn->dir.subdirs + 2);
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}
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int kernfs_iop_getattr(const struct path *path, struct kstat *stat,
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u32 request_mask, unsigned int query_flags)
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{
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struct inode *inode = d_inode(path->dentry);
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struct kernfs_node *kn = inode->i_private;
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mutex_lock(&kernfs_mutex);
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kernfs_refresh_inode(kn, inode);
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mutex_unlock(&kernfs_mutex);
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generic_fillattr(inode, stat);
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return 0;
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}
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static void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode)
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{
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kernfs_get(kn);
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inode->i_private = kn;
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inode->i_mapping->a_ops = &kernfs_aops;
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inode->i_op = &kernfs_iops;
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inode->i_generation = kernfs_gen(kn);
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set_default_inode_attr(inode, kn->mode);
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kernfs_refresh_inode(kn, inode);
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/* initialize inode according to type */
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switch (kernfs_type(kn)) {
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case KERNFS_DIR:
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inode->i_op = &kernfs_dir_iops;
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inode->i_fop = &kernfs_dir_fops;
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if (kn->flags & KERNFS_EMPTY_DIR)
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make_empty_dir_inode(inode);
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break;
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case KERNFS_FILE:
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inode->i_size = kn->attr.size;
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inode->i_fop = &kernfs_file_fops;
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break;
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case KERNFS_LINK:
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inode->i_op = &kernfs_symlink_iops;
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break;
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default:
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BUG();
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}
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unlock_new_inode(inode);
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}
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/**
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* kernfs_get_inode - get inode for kernfs_node
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* @sb: super block
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* @kn: kernfs_node to allocate inode for
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*
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* Get inode for @kn. If such inode doesn't exist, a new inode is
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* allocated and basics are initialized. New inode is returned
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* locked.
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*
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* LOCKING:
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* Kernel thread context (may sleep).
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*
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* RETURNS:
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* Pointer to allocated inode on success, NULL on failure.
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*/
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struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn)
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{
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struct inode *inode;
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inode = iget_locked(sb, kernfs_ino(kn));
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if (inode && (inode->i_state & I_NEW))
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kernfs_init_inode(kn, inode);
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return inode;
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}
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/*
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* The kernfs_node serves as both an inode and a directory entry for
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* kernfs. To prevent the kernfs inode numbers from being freed
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* prematurely we take a reference to kernfs_node from the kernfs inode. A
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* super_operations.evict_inode() implementation is needed to drop that
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* reference upon inode destruction.
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*/
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void kernfs_evict_inode(struct inode *inode)
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{
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struct kernfs_node *kn = inode->i_private;
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truncate_inode_pages_final(&inode->i_data);
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clear_inode(inode);
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kernfs_put(kn);
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}
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int kernfs_iop_permission(struct inode *inode, int mask)
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{
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struct kernfs_node *kn;
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if (mask & MAY_NOT_BLOCK)
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return -ECHILD;
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kn = inode->i_private;
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mutex_lock(&kernfs_mutex);
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kernfs_refresh_inode(kn, inode);
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mutex_unlock(&kernfs_mutex);
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return generic_permission(inode, mask);
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}
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int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
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void *value, size_t size)
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{
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struct kernfs_iattrs *attrs = kernfs_iattrs_noalloc(kn);
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if (!attrs)
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return -ENODATA;
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return simple_xattr_get(&attrs->xattrs, name, value, size);
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}
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int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
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const void *value, size_t size, int flags)
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{
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struct kernfs_iattrs *attrs = kernfs_iattrs(kn);
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if (!attrs)
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return -ENOMEM;
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return simple_xattr_set(&attrs->xattrs, name, value, size, flags, NULL);
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}
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static int kernfs_vfs_xattr_get(const struct xattr_handler *handler,
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struct dentry *unused, struct inode *inode,
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const char *suffix, void *value, size_t size)
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{
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const char *name = xattr_full_name(handler, suffix);
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struct kernfs_node *kn = inode->i_private;
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return kernfs_xattr_get(kn, name, value, size);
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}
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static int kernfs_vfs_xattr_set(const struct xattr_handler *handler,
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struct dentry *unused, struct inode *inode,
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const char *suffix, const void *value,
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size_t size, int flags)
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{
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const char *name = xattr_full_name(handler, suffix);
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struct kernfs_node *kn = inode->i_private;
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return kernfs_xattr_set(kn, name, value, size, flags);
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}
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static int kernfs_vfs_user_xattr_add(struct kernfs_node *kn,
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const char *full_name,
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struct simple_xattrs *xattrs,
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const void *value, size_t size, int flags)
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{
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atomic_t *sz = &kn->iattr->user_xattr_size;
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atomic_t *nr = &kn->iattr->nr_user_xattrs;
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ssize_t removed_size;
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int ret;
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if (atomic_inc_return(nr) > KERNFS_MAX_USER_XATTRS) {
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ret = -ENOSPC;
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goto dec_count_out;
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}
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if (atomic_add_return(size, sz) > KERNFS_USER_XATTR_SIZE_LIMIT) {
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ret = -ENOSPC;
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goto dec_size_out;
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}
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ret = simple_xattr_set(xattrs, full_name, value, size, flags,
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&removed_size);
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if (!ret && removed_size >= 0)
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size = removed_size;
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else if (!ret)
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return 0;
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dec_size_out:
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atomic_sub(size, sz);
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dec_count_out:
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atomic_dec(nr);
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return ret;
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}
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static int kernfs_vfs_user_xattr_rm(struct kernfs_node *kn,
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const char *full_name,
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struct simple_xattrs *xattrs,
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const void *value, size_t size, int flags)
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{
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atomic_t *sz = &kn->iattr->user_xattr_size;
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atomic_t *nr = &kn->iattr->nr_user_xattrs;
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ssize_t removed_size;
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int ret;
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ret = simple_xattr_set(xattrs, full_name, value, size, flags,
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&removed_size);
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if (removed_size >= 0) {
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atomic_sub(removed_size, sz);
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atomic_dec(nr);
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}
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return ret;
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}
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static int kernfs_vfs_user_xattr_set(const struct xattr_handler *handler,
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struct dentry *unused, struct inode *inode,
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const char *suffix, const void *value,
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size_t size, int flags)
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{
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const char *full_name = xattr_full_name(handler, suffix);
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struct kernfs_node *kn = inode->i_private;
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struct kernfs_iattrs *attrs;
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if (!(kernfs_root(kn)->flags & KERNFS_ROOT_SUPPORT_USER_XATTR))
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return -EOPNOTSUPP;
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attrs = kernfs_iattrs(kn);
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if (!attrs)
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return -ENOMEM;
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if (value)
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return kernfs_vfs_user_xattr_add(kn, full_name, &attrs->xattrs,
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value, size, flags);
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else
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return kernfs_vfs_user_xattr_rm(kn, full_name, &attrs->xattrs,
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value, size, flags);
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}
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static const struct xattr_handler kernfs_trusted_xattr_handler = {
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.prefix = XATTR_TRUSTED_PREFIX,
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.get = kernfs_vfs_xattr_get,
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.set = kernfs_vfs_xattr_set,
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};
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static const struct xattr_handler kernfs_security_xattr_handler = {
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.prefix = XATTR_SECURITY_PREFIX,
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.get = kernfs_vfs_xattr_get,
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.set = kernfs_vfs_xattr_set,
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};
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static const struct xattr_handler kernfs_user_xattr_handler = {
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.prefix = XATTR_USER_PREFIX,
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.get = kernfs_vfs_xattr_get,
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.set = kernfs_vfs_user_xattr_set,
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};
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const struct xattr_handler *kernfs_xattr_handlers[] = {
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&kernfs_trusted_xattr_handler,
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&kernfs_security_xattr_handler,
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&kernfs_user_xattr_handler,
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NULL
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};
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