linux-stable/fs/internal.h
Christian Brauner 9d9539db86 pidfs: remove config option
As Linus suggested this enables pidfs unconditionally. A key property to
retain is the ability to compare pidfds by inode number (cf. [1]).
That's extremely helpful just as comparing namespace file descriptors by
inode number is. They are used in a variety of scenarios where they need
to be compared, e.g., when receiving a pidfd via SO_PEERPIDFD from a
socket to trivially authenticate a the sender and various other
use-cases.

For 64bit systems this is pretty trivial to do. For 32bit it's slightly
more annoying as we discussed but we simply add a dumb ida based
allocator that gets used on 32bit. This gives the same guarantees about
inode numbers on 64bit without any overflow risk. Practically, we'll
never run into overflow issues because we're constrained by the number
of processes that can exist on 32bit and by the number of open files
that can exist on a 32bit system. On 64bit none of this matters and
things are very simple.

If 32bit also needs the uniqueness guarantee they can simply parse the
contents of /proc/<pid>/fd/<nr>. The uniqueness guarantees have a
variety of use-cases. One of the most obvious ones is that they will
make pidfiles (or "pidfdfiles", I guess) reliable as the unique
identifier can be placed into there that won't be reycled. Also a
frequent request.

Note, I took the chance and simplified path_from_stashed() even further.
Instead of passing the inode number explicitly to path_from_stashed() we
let the filesystem handle that internally. So path_from_stashed() ends
up even simpler than it is now. This is also a good solution allowing
the cleanup code to be clean and consistent between 32bit and 64bit. The
cleanup path in prepare_anon_dentry() is also switched around so we put
the inode before the dentry allocation. This means we only have to call
the cleanup handler for the filesystem's inode data once and can rely
->evict_inode() otherwise.

Aside from having to have a bit of extra code for 32bit it actually ends
up a nice cleanup for path_from_stashed() imho.

Tested on both 32 and 64bit including error injection.

Link: https://github.com/systemd/systemd/pull/31713 [1]
Link: https://lore.kernel.org/r/20240312-dingo-sehnlich-b3ecc35c6de7@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2024-03-13 12:53:53 -07:00

320 lines
9.4 KiB
C

/* SPDX-License-Identifier: GPL-2.0-or-later */
/* fs/ internal definitions
*
* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
struct super_block;
struct file_system_type;
struct iomap;
struct iomap_ops;
struct linux_binprm;
struct path;
struct mount;
struct shrink_control;
struct fs_context;
struct pipe_inode_info;
struct iov_iter;
struct mnt_idmap;
/*
* block/bdev.c
*/
#ifdef CONFIG_BLOCK
extern void __init bdev_cache_init(void);
#else
static inline void bdev_cache_init(void)
{
}
#endif /* CONFIG_BLOCK */
/*
* buffer.c
*/
int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
get_block_t *get_block, const struct iomap *iomap);
/*
* char_dev.c
*/
extern void __init chrdev_init(void);
/*
* fs_context.c
*/
extern const struct fs_context_operations legacy_fs_context_ops;
extern int parse_monolithic_mount_data(struct fs_context *, void *);
extern void vfs_clean_context(struct fs_context *fc);
extern int finish_clean_context(struct fs_context *fc);
/*
* namei.c
*/
extern int filename_lookup(int dfd, struct filename *name, unsigned flags,
struct path *path, struct path *root);
int do_rmdir(int dfd, struct filename *name);
int do_unlinkat(int dfd, struct filename *name);
int may_linkat(struct mnt_idmap *idmap, const struct path *link);
int do_renameat2(int olddfd, struct filename *oldname, int newdfd,
struct filename *newname, unsigned int flags);
int do_mkdirat(int dfd, struct filename *name, umode_t mode);
int do_symlinkat(struct filename *from, int newdfd, struct filename *to);
int do_linkat(int olddfd, struct filename *old, int newdfd,
struct filename *new, int flags);
/*
* namespace.c
*/
extern struct vfsmount *lookup_mnt(const struct path *);
extern int finish_automount(struct vfsmount *, const struct path *);
extern int sb_prepare_remount_readonly(struct super_block *);
extern void __init mnt_init(void);
int mnt_get_write_access_file(struct file *file);
void mnt_put_write_access_file(struct file *file);
extern void dissolve_on_fput(struct vfsmount *);
extern bool may_mount(void);
int path_mount(const char *dev_name, struct path *path,
const char *type_page, unsigned long flags, void *data_page);
int path_umount(struct path *path, int flags);
int show_path(struct seq_file *m, struct dentry *root);
/*
* fs_struct.c
*/
extern void chroot_fs_refs(const struct path *, const struct path *);
/*
* file_table.c
*/
struct file *alloc_empty_file(int flags, const struct cred *cred);
struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred);
struct file *alloc_empty_backing_file(int flags, const struct cred *cred);
static inline void file_put_write_access(struct file *file)
{
put_write_access(file->f_inode);
mnt_put_write_access(file->f_path.mnt);
if (unlikely(file->f_mode & FMODE_BACKING))
mnt_put_write_access(backing_file_user_path(file)->mnt);
}
static inline void put_file_access(struct file *file)
{
if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
i_readcount_dec(file->f_inode);
} else if (file->f_mode & FMODE_WRITER) {
file_put_write_access(file);
}
}
/*
* super.c
*/
extern int reconfigure_super(struct fs_context *);
extern bool super_trylock_shared(struct super_block *sb);
struct super_block *user_get_super(dev_t, bool excl);
void put_super(struct super_block *sb);
extern bool mount_capable(struct fs_context *);
int sb_init_dio_done_wq(struct super_block *sb);
/*
* Prepare superblock for changing its read-only state (i.e., either remount
* read-write superblock read-only or vice versa). After this function returns
* mnt_is_readonly() will return true for any mount of the superblock if its
* caller is able to observe any changes done by the remount. This holds until
* sb_end_ro_state_change() is called.
*/
static inline void sb_start_ro_state_change(struct super_block *sb)
{
WRITE_ONCE(sb->s_readonly_remount, 1);
/*
* For RO->RW transition, the barrier pairs with the barrier in
* mnt_is_readonly() making sure if mnt_is_readonly() sees SB_RDONLY
* cleared, it will see s_readonly_remount set.
* For RW->RO transition, the barrier pairs with the barrier in
* mnt_get_write_access() before the mnt_is_readonly() check.
* The barrier makes sure if mnt_get_write_access() sees MNT_WRITE_HOLD
* already cleared, it will see s_readonly_remount set.
*/
smp_wmb();
}
/*
* Ends section changing read-only state of the superblock. After this function
* returns if mnt_is_readonly() returns false, the caller will be able to
* observe all the changes remount did to the superblock.
*/
static inline void sb_end_ro_state_change(struct super_block *sb)
{
/*
* This barrier provides release semantics that pairs with
* the smp_rmb() acquire semantics in mnt_is_readonly().
* This barrier pair ensure that when mnt_is_readonly() sees
* 0 for sb->s_readonly_remount, it will also see all the
* preceding flag changes that were made during the RO state
* change.
*/
smp_wmb();
WRITE_ONCE(sb->s_readonly_remount, 0);
}
/*
* open.c
*/
struct open_flags {
int open_flag;
umode_t mode;
int acc_mode;
int intent;
int lookup_flags;
};
extern struct file *do_filp_open(int dfd, struct filename *pathname,
const struct open_flags *op);
extern struct file *do_file_open_root(const struct path *,
const char *, const struct open_flags *);
extern struct open_how build_open_how(int flags, umode_t mode);
extern int build_open_flags(const struct open_how *how, struct open_flags *op);
struct file *file_close_fd_locked(struct files_struct *files, unsigned fd);
long do_ftruncate(struct file *file, loff_t length, int small);
long do_sys_ftruncate(unsigned int fd, loff_t length, int small);
int chmod_common(const struct path *path, umode_t mode);
int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group,
int flag);
int chown_common(const struct path *path, uid_t user, gid_t group);
extern int vfs_open(const struct path *, struct file *);
/*
* inode.c
*/
extern long prune_icache_sb(struct super_block *sb, struct shrink_control *sc);
int dentry_needs_remove_privs(struct mnt_idmap *, struct dentry *dentry);
bool in_group_or_capable(struct mnt_idmap *idmap,
const struct inode *inode, vfsgid_t vfsgid);
/*
* fs-writeback.c
*/
extern long get_nr_dirty_inodes(void);
void invalidate_inodes(struct super_block *sb);
/*
* dcache.c
*/
extern int d_set_mounted(struct dentry *dentry);
extern long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc);
extern struct dentry *d_alloc_cursor(struct dentry *);
extern struct dentry * d_alloc_pseudo(struct super_block *, const struct qstr *);
extern char *simple_dname(struct dentry *, char *, int);
extern void dput_to_list(struct dentry *, struct list_head *);
extern void shrink_dentry_list(struct list_head *);
extern void shrink_dcache_for_umount(struct super_block *);
extern struct dentry *__d_lookup(const struct dentry *, const struct qstr *);
extern struct dentry *__d_lookup_rcu(const struct dentry *parent,
const struct qstr *name, unsigned *seq);
extern void d_genocide(struct dentry *);
/*
* pipe.c
*/
extern const struct file_operations pipefifo_fops;
/*
* fs_pin.c
*/
extern void group_pin_kill(struct hlist_head *p);
extern void mnt_pin_kill(struct mount *m);
/*
* fs/nsfs.c
*/
extern const struct dentry_operations ns_dentry_operations;
/*
* fs/stat.c:
*/
int getname_statx_lookup_flags(int flags);
int do_statx(int dfd, struct filename *filename, unsigned int flags,
unsigned int mask, struct statx __user *buffer);
/*
* fs/splice.c:
*/
ssize_t splice_file_to_pipe(struct file *in,
struct pipe_inode_info *opipe,
loff_t *offset,
size_t len, unsigned int flags);
/*
* fs/xattr.c:
*/
struct xattr_name {
char name[XATTR_NAME_MAX + 1];
};
struct xattr_ctx {
/* Value of attribute */
union {
const void __user *cvalue;
void __user *value;
};
void *kvalue;
size_t size;
/* Attribute name */
struct xattr_name *kname;
unsigned int flags;
};
ssize_t do_getxattr(struct mnt_idmap *idmap,
struct dentry *d,
struct xattr_ctx *ctx);
int setxattr_copy(const char __user *name, struct xattr_ctx *ctx);
int do_setxattr(struct mnt_idmap *idmap, struct dentry *dentry,
struct xattr_ctx *ctx);
int may_write_xattr(struct mnt_idmap *idmap, struct inode *inode);
#ifdef CONFIG_FS_POSIX_ACL
int do_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
const char *acl_name, const void *kvalue, size_t size);
ssize_t do_get_acl(struct mnt_idmap *idmap, struct dentry *dentry,
const char *acl_name, void *kvalue, size_t size);
#else
static inline int do_set_acl(struct mnt_idmap *idmap,
struct dentry *dentry, const char *acl_name,
const void *kvalue, size_t size)
{
return -EOPNOTSUPP;
}
static inline ssize_t do_get_acl(struct mnt_idmap *idmap,
struct dentry *dentry, const char *acl_name,
void *kvalue, size_t size)
{
return -EOPNOTSUPP;
}
#endif
ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *pos);
/*
* fs/attr.c
*/
struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns);
struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap);
void mnt_idmap_put(struct mnt_idmap *idmap);
struct stashed_operations {
void (*put_data)(void *data);
int (*init_inode)(struct inode *inode, void *data);
};
int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data,
struct path *path);
void stashed_dentry_prune(struct dentry *dentry);