Changes in Makefile

cd051cfe1e35a471fc2cdf6d32fae6ee23305ecb - Merge tag 'vfs-7.3-rc1.failfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Mon, 17 Aug 2026 18:15:52 +0200

Merge tag 'vfs-7.3-rc1.failfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfsPull 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 List of files: /linux/tools/testing/selftests/filesystems/failfs/Makefile

1d38e750a389e919c1608dbc61cd5c93cd4915dc - Merge patch series "fs: add failfs"

Mon, 27 Jul 2026 11:49:54 +0200

Merge patch series "fs: add failfs"Christian Brauner says:nullfs provides a permanently empty and immutable directory. Lookupsfail with ENOENT. The directory can be opened, read, stat, mounted upon.It behaves like nothing is there.Add its counterpart failfs where the semantics are not "there isnothing here" but "nothing is supported here". Every operation thatreaches the filesystem fails with EOPNOTSUPP. Even statfs()/fstatfs()fail so the filesystem cannot be discovered through an fd to it.EOPNOTSUPP rather than a permission errno keeps that coherent. Thereis no permission model in which anything could ever be allowed andEACCES or EPERM would merely suggest that different credentials mightsucceed while EIO would suggest corruption. It also makes hitting thefailfs boundary mostly quite dinstinguishable. A task anchoring itslookups at real directory file descriptors may be able to tell a failfsrefusal from an ordinary permission failure. I wouldn't go so far asguaranteeing that but it should mostly work.The root cannot be opened at all not even with O_PATH. It is neverreached by a lookup in a parent directory. The only way to a path-walkterminal at the root is a jump through a /proc//{root,cwd} magiclink or by mountpoint traversal. The root also refuses->d_weak_revalidate() which the VFS calls for jumped terminals. Thatcloses every remaining way to reference it. An O_PATHopen is refused and name_to_handle_at() cannot encode it into a filehandle, and following a magic link into it fails. A plain readlink() ofsuch a link still works and shows "failfs:/".There is a single instance of failfs mounted during early boot viakern_mount() making it logically distinct from every mount namespace.Since the mount is a member of no mount namespace mounting onto itfails. So nothing can ever be mounted on top of it. It cannot be clonedvia OPEN_TREE_CLONE and it does not show up in statmount()/listmount()or /proc//mountinfo. The filesystem is not registered so it isnot visible in /proc/filesystems and cannot be mounted from userspace.This lets tasks shed their filesystem state completely. A process withits root directory or working directory in failfs must anchor every pathlookup at an explicit file descriptor or is doomed to fail any lookup.Absolute paths, absolute symlinks, and AT_FDCWD-relative lookupssimply fail. Followup patches will expose it via a new FD_FAILFS_ROOTfile descriptor sentinel understood by fchdir() and the new fchroot()system call.Fun fact, because of how dynamic binary execution work with PT_INTERPthis also currently prevents execution of dynamic binaries becauseloaders have absolute paths (see selftests).* patches from https://patch.msgid.link/20260724-work-failfs-v2-0-485dabbae185@kernel.org: 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 failfsLink: https://patch.msgid.link/20260724-work-failfs-v2-0-485dabbae185@kernel.orgSigned-off-by: Christian Brauner (Amutable) List of files: /linux/tools/testing/selftests/filesystems/failfs/Makefile

df4b2889ea9a1ef809bfb7e1401e2cdc475956c8 - selftests/filesystems: add failfs selftests

Fri, 24 Jul 2026 15:41:22 +0200

selftests/filesystems: add failfs selftestsTest the failfs semantics and both new entry points:- fchdir(FD_FAILFS_ROOT): * working directory lookups and getcwd() fail * other sentinels are rejected * the state is recoverable while the root is untouched- fchroot() with regular fds: * chroot parity * CAP_SYS_CHROOT required * ENOTDIR/EBADF/EINVAL checks- fchroot(FD_FAILFS_ROOT): * absolute lookups, stat, statfs and opens of the root including O_PATH fail with EOPNOTSUPP * dirfd-anchored I/O keeps working * ".." walks clamp at the top of the mount tree * /proc magic links resolve but can't be stat through * absolute symlinks fail while relative symlinks keep resolving- Unprivileged entry requires no_new_privs and is rejected for chrooted callers and for a shared fs_struct- entering makes the task count as chrooted so user namespace creation fails- Nothing can be mounted on top of failfs and OPEN_TREE_CLONE is rejected; the overmount test runs in a private mount namespace so a regression cannot touch the host root- setns() to a kept mount namespace fd restores root and working directory- The failfs root is inherited across fork() and absolute exec fails- Exec by fd of a dynamically linked binary fails on opening its absolute PT_INTERP interpreterThe exec tests run the exec in a child so a wrongly successful execcannot replace the test image and masquerade as a pass.Link: https://patch.msgid.link/20260724-work-failfs-v2-6-485dabbae185@kernel.orgSigned-off-by: Christian Brauner (Amutable) List of files: /linux/tools/testing/selftests/filesystems/failfs/Makefile