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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>
128 lines
3.4 KiB
C
128 lines
3.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* fs/kernfs/kernfs-internal.h - kernfs internal header file
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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 <teheo@suse.de>
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*/
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#ifndef __KERNFS_INTERNAL_H
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#define __KERNFS_INTERNAL_H
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#include <linux/lockdep.h>
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#include <linux/fs.h>
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#include <linux/mutex.h>
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#include <linux/xattr.h>
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#include <linux/kernfs.h>
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#include <linux/fs_context.h>
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struct kernfs_iattrs {
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kuid_t ia_uid;
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kgid_t ia_gid;
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struct timespec64 ia_atime;
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struct timespec64 ia_mtime;
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struct timespec64 ia_ctime;
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struct simple_xattrs xattrs;
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atomic_t nr_user_xattrs;
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atomic_t user_xattr_size;
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};
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/* +1 to avoid triggering overflow warning when negating it */
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#define KN_DEACTIVATED_BIAS (INT_MIN + 1)
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/* KERNFS_TYPE_MASK and types are defined in include/linux/kernfs.h */
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/**
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* kernfs_root - find out the kernfs_root a kernfs_node belongs to
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* @kn: kernfs_node of interest
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*
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* Return the kernfs_root @kn belongs to.
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*/
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static inline struct kernfs_root *kernfs_root(struct kernfs_node *kn)
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{
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/* if parent exists, it's always a dir; otherwise, @sd is a dir */
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if (kn->parent)
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kn = kn->parent;
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return kn->dir.root;
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}
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/*
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* mount.c
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*/
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struct kernfs_super_info {
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struct super_block *sb;
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/*
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* The root associated with this super_block. Each super_block is
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* identified by the root and ns it's associated with.
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*/
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struct kernfs_root *root;
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/*
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* Each sb is associated with one namespace tag, currently the
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* network namespace of the task which mounted this kernfs
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* instance. If multiple tags become necessary, make the following
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* an array and compare kernfs_node tag against every entry.
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*/
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const void *ns;
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/* anchored at kernfs_root->supers, protected by kernfs_mutex */
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struct list_head node;
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};
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#define kernfs_info(SB) ((struct kernfs_super_info *)(SB->s_fs_info))
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static inline struct kernfs_node *kernfs_dentry_node(struct dentry *dentry)
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{
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if (d_really_is_negative(dentry))
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return NULL;
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return d_inode(dentry)->i_private;
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}
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extern const struct super_operations kernfs_sops;
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extern struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;
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/*
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* inode.c
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*/
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extern const struct xattr_handler *kernfs_xattr_handlers[];
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void kernfs_evict_inode(struct inode *inode);
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int kernfs_iop_permission(struct inode *inode, int mask);
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int kernfs_iop_setattr(struct dentry *dentry, struct iattr *iattr);
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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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ssize_t kernfs_iop_listxattr(struct dentry *dentry, char *buf, size_t size);
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int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
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/*
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* dir.c
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*/
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extern struct mutex kernfs_mutex;
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extern const struct dentry_operations kernfs_dops;
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extern const struct file_operations kernfs_dir_fops;
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extern const struct inode_operations kernfs_dir_iops;
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struct kernfs_node *kernfs_get_active(struct kernfs_node *kn);
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void kernfs_put_active(struct kernfs_node *kn);
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int kernfs_add_one(struct kernfs_node *kn);
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struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
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const char *name, umode_t mode,
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kuid_t uid, kgid_t gid,
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unsigned flags);
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/*
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* file.c
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*/
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extern const struct file_operations kernfs_file_fops;
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void kernfs_drain_open_files(struct kernfs_node *kn);
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/*
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* symlink.c
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*/
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extern const struct inode_operations kernfs_symlink_iops;
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#endif /* __KERNFS_INTERNAL_H */
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