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Merge tag 'vfs-7.3-rc1.failfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

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Pull failfs filesystem from Christian Brauner:
 "Add failfs and expose a FD_FAILFS_ROOT sentinel.

  This allows userspace to shed their filesystem state completely. A
  process with its root or working directory in failfs must anchor every
  path lookup at an explicit file descriptor. Absolute paths, absolute
  symlinks and AT_FDCWD-relative lookups simply fail.

  Failfs is the counterpart to nullfs. nullfs says adds a permanently
  empty, immutable directory whose lookups fail with ENOENT but which
  can be opened, read, stat'd and mounted upon. Failfs on the other hand
  fails every operation. The root cannot be opened at all. A single
  instance is mounted during early boot via kern_mount(), which makes it
  logically distinct from every mount namespace.

  This is accompanied by a new fchroot() system call which makes
  chrooting via a file descriptor a first class concept. It's possible
  to chroot into failfs as an unprivileged user provided the task has no
  new privileges set"

* tag 'vfs-7.3-rc1.failfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  Documentation: add failfs documentation
  selftests/filesystems: add failfs selftests
  arch: hookup fchroot() system call
  fs: support FD_FAILFS_ROOT in fchroot()
  fs: add fchroot()
  fs: support FD_FAILFS_ROOT in fchdir()
  fs: add failfs
This commit is contained in:
Linus Torvalds
2026-08-17 09:15:52 -07:00
parent d31a688a49 1d38e750a3
commit cd051cfe1e
44 changed files with 931 additions and 5 deletions
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6
include/uapi/asm-generic/unistd.h
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@@ -863,8 +863,12 @@ __SYSCALL(__NR_listns, sys_listns)
#define __NR_rseq_slice_yield 471
__SYSCALL(__NR_rseq_slice_yield, sys_rseq_slice_yield)
/* fs/open.c */
#define __NR_fchroot 472
__SYSCALL(__NR_fchroot, sys_fchroot)
#undef __NR_syscalls
#define __NR_syscalls 472
#define __NR_syscalls 473
/*
* 32 bit systems traditionally used different

1
include/uapi/linux/fcntl.h
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@@ -124,6 +124,7 @@ struct delegation {
#define FD_PIDFS_ROOT -10002 /* Root of the pidfs filesystem */
#define FD_NSFS_ROOT -10003 /* Root of the nsfs filesystem */
#define FD_FAILFS_ROOT -10004 /* Root of the failfs filesystem */
#define FD_INVALID -10009 /* Invalid file descriptor: -10000 - EBADF = -10009 */
/* Generic flags for the *at(2) family of syscalls. */

1
include/uapi/linux/magic.h
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@@ -105,5 +105,6 @@
#define PID_FS_MAGIC 0x50494446 /* "PIDF" */
#define GUEST_MEMFD_MAGIC 0x474d454d /* "GMEM" */
#define NULL_FS_MAGIC 0x4E554C4C /* "NULL" */
#define FAIL_FS_MAGIC 0x4641494C /* "FAIL" */
#endif /* __LINUX_MAGIC_H__ */