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76fdb7eb4e
The root inode of /proc having a fixed inode number has been part of the
core kernel ABI since its inception, and recently some userspace
programs (mainly container runtimes) have started to explicitly depend
on this behaviour.
The main reason this is useful to userspace is that by checking that a
suspect /proc handle has fstype PROC_SUPER_MAGIC and is PROCFS_ROOT_INO,
they can then use openat2(RESOLVE_{NO_{XDEV,MAGICLINK},BENEATH}) to
ensure that there isn't a bind-mount that replaces some procfs file with
a different one. This kind of attack has lead to security issues in
container runtimes in the past (such as CVE-2019-19921) and libraries
like libpathrs[1] use this feature of procfs to provide safe procfs
handling functions.
There was also some trailing whitespace in the "struct proc_dir_entry"
initialiser, so fix that up as well.
[1]: https://github.com/openSUSE/libpathrs
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Link: https://lore.kernel.org/20250708-uapi-procfs-root-ino-v1-1-6ae61e97c79b@cyphar.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
90 lines
2.6 KiB
C
90 lines
2.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* procfs namespace bits
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*/
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#ifndef _LINUX_PROC_NS_H
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#define _LINUX_PROC_NS_H
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#include <linux/ns_common.h>
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#include <uapi/linux/nsfs.h>
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struct pid_namespace;
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struct nsset;
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struct path;
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struct task_struct;
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struct inode;
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struct proc_ns_operations {
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const char *name;
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const char *real_ns_name;
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int type;
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struct ns_common *(*get)(struct task_struct *task);
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void (*put)(struct ns_common *ns);
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int (*install)(struct nsset *nsset, struct ns_common *ns);
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struct user_namespace *(*owner)(struct ns_common *ns);
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struct ns_common *(*get_parent)(struct ns_common *ns);
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} __randomize_layout;
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extern const struct proc_ns_operations netns_operations;
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extern const struct proc_ns_operations utsns_operations;
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extern const struct proc_ns_operations ipcns_operations;
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extern const struct proc_ns_operations pidns_operations;
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extern const struct proc_ns_operations pidns_for_children_operations;
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extern const struct proc_ns_operations userns_operations;
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extern const struct proc_ns_operations mntns_operations;
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extern const struct proc_ns_operations cgroupns_operations;
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extern const struct proc_ns_operations timens_operations;
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extern const struct proc_ns_operations timens_for_children_operations;
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/*
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* We always define these enumerators
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*/
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enum {
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PROC_IPC_INIT_INO = IPC_NS_INIT_INO,
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PROC_UTS_INIT_INO = UTS_NS_INIT_INO,
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PROC_USER_INIT_INO = USER_NS_INIT_INO,
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PROC_PID_INIT_INO = PID_NS_INIT_INO,
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PROC_CGROUP_INIT_INO = CGROUP_NS_INIT_INO,
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PROC_TIME_INIT_INO = TIME_NS_INIT_INO,
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PROC_NET_INIT_INO = NET_NS_INIT_INO,
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PROC_MNT_INIT_INO = MNT_NS_INIT_INO,
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};
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#ifdef CONFIG_PROC_FS
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extern int proc_alloc_inum(unsigned int *pino);
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extern void proc_free_inum(unsigned int inum);
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#else /* CONFIG_PROC_FS */
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static inline int proc_alloc_inum(unsigned int *inum)
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{
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*inum = 1;
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return 0;
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}
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static inline void proc_free_inum(unsigned int inum) {}
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#endif /* CONFIG_PROC_FS */
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static inline int ns_alloc_inum(struct ns_common *ns)
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{
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WRITE_ONCE(ns->stashed, NULL);
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return proc_alloc_inum(&ns->inum);
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}
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#define ns_free_inum(ns) proc_free_inum((ns)->inum)
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#define get_proc_ns(inode) ((struct ns_common *)(inode)->i_private)
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extern int ns_get_path(struct path *path, struct task_struct *task,
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const struct proc_ns_operations *ns_ops);
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typedef struct ns_common *ns_get_path_helper_t(void *);
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extern int ns_get_path_cb(struct path *path, ns_get_path_helper_t ns_get_cb,
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void *private_data);
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extern bool ns_match(const struct ns_common *ns, dev_t dev, ino_t ino);
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extern int ns_get_name(char *buf, size_t size, struct task_struct *task,
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const struct proc_ns_operations *ns_ops);
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extern void nsfs_init(void);
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#endif /* _LINUX_PROC_NS_H */
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