kernel/include/linux/mount.h, branch linux-6.16.y

replace collect_mounts()/drop_collected_mounts() with a safer variant

2025-06-23T18:01:49Z

collect_mounts() has several problems - one can't iterate over the results directly, so it has to be done with callback passed to iterate_mounts(); it has an oopsable race with d_invalidate(); it creates temporary clones of mounts invisibly for sync umount (IOW, you can have non-lazy umount succeed leaving filesystem not mounted anywhere and yet still busy). A saner approach is to give caller an array of struct path that would pin every mount in a subtree, without cloning any mounts. * collect_mounts()/drop_collected_mounts()/iterate_mounts() is gone * collect_paths(where, preallocated, size) gives either ERR_PTR(-E...) or a pointer to array of struct path, one for each chunk of tree visible under 'where' (i.e. the first element is a copy of where, followed by (mount,root) for everything mounted under it - the same set collect_mounts() would give). Unlike collect_mounts(), the mounts are *not* cloned - we just get pinning references to the roots of subtrees in the caller's namespace. Array is terminated by {NULL, NULL} struct path. If it fits into preallocated array (on-stack, normally), that's where it goes; otherwise it's allocated by kmalloc_array(). Passing 0 as size means that 'preallocated' is ignored (and expected to be NULL). * drop_collected_paths(paths, preallocated) is given the array returned by an earlier call of collect_paths() and the preallocated array passed to that call. All mount/dentry references are dropped and array is kfree'd if it's not equal to 'preallocated'. * instead of iterate_mounts(), users should just iterate over array of struct path - nothing exotic is needed for that. Existing users (all in audit_tree.c) are converted. [folded a fix for braino reported by Venkat Rao Bagalkote ] Fixes: 80b5dce8c59b0 ("vfs: Add a function to lazily unmount all mounts from any dentry") Tested-by: Venkat Rao Bagalkote Signed-off-by: Al Viro

Merge tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2025-06-08T17:35:12Z

Pull mount fixes from Al Viro: "Various mount-related bugfixes: - split the do_move_mount() checks in subtree-of-our-ns and entire-anon cases and adapt detached mount propagation selftest for mount_setattr - allow clone_private_mount() for a path on real rootfs - fix a race in call of has_locked_children() - fix move_mount propagation graph breakage by MOVE_MOUNT_SET_GROUP - make sure clone_private_mnt() caller has CAP_SYS_ADMIN in the right userns - avoid false negatives in path_overmount() - don't leak MNT_LOCKED from parent to child in finish_automount() - do_change_type(): refuse to operate on unmounted/not ours mounts" * tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: do_change_type(): refuse to operate on unmounted/not ours mounts clone_private_mnt(): make sure that caller has CAP_SYS_ADMIN in the right userns selftests/mount_setattr: adapt detached mount propagation test do_move_mount(): split the checks in subtree-of-our-ns and entire-anon cases fs: allow clone_private_mount() for a path on real rootfs fix propagation graph breakage by MOVE_MOUNT_SET_GROUP move_mount(2) finish_automount(): don't leak MNT_LOCKED from parent to child path_overmount(): avoid false negatives fs/fhandle.c: fix a race in call of has_locked_children()

finish_automount(): don't leak MNT_LOCKED from parent to child

2025-06-07T04:40:25Z

Intention for MNT_LOCKED had always been to protect the internal mountpoints within a subtree that got copied across the userns boundary, not the mountpoint that tree got attached to - after all, it _was_ exposed before the copying. For roots of secondary copies that is enforced in attach_recursive_mnt() - MNT_LOCKED is explicitly stripped for those. For the root of primary copy we are almost always guaranteed that MNT_LOCKED won't be there, so attach_recursive_mnt() doesn't bother. Unfortunately, one call chain got overlooked - triggering e.g. NFS referral will have the submount inherit the public flags from parent; that's fine for such things as read-only, nosuid, etc., but not for MNT_LOCKED. This is particularly pointless since the mount attached by finish_automount() is usually expirable, which makes any protection granted by MNT_LOCKED null and void; just wait for a while and that mount will go away on its own. Include MNT_LOCKED into the set of flags to be ignored by do_add_mount() - it really is an internal flag. Reviewed-by: Christian Brauner Fixes: 5ff9d8a65ce8 ("vfs: Lock in place mounts from more privileged users") Signed-off-by: Al Viro

Merge tag 'pull-automount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2025-05-30T22:38:29Z

Pull automount updates from Al Viro: "Automount wart removal A bunch of odd boilerplate gone from instances - the reason for those was the need to protect the yet-to-be-attched mount from mark_mounts_for_expiry() deciding to take it out. But that's easy to detect and take care of in mark_mounts_for_expiry() itself; no need to have every instance simulate mount being busy by grabbing an extra reference to it, with finish_automount() undoing that once it attaches that mount. Should've done it that way from the very beginning... This is a flagday change, thankfully there are very few instances. vfs_submount() is gone - its sole remaining user (trace_automount) had been switched to saner primitives" * tag 'pull-automount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: kill vfs_submount() saner calling conventions for ->d_automount()

fs: convert mount flags to enum

2025-05-23T12:20:44Z

In prior kernel versions (5.8-6.8), commit 9f6c61f96f2d9 ("proc/mounts: add cursor") introduced MNT_CURSOR, a flag used by readers from /proc/mounts to keep their place while reading the file. Later, commit 2eea9ce4310d8 ("mounts: keep list of mounts in an rbtree") removed this flag and its value has since been repurposed. For debuggers iterating over the list of mounts, cursors should be skipped as they are irrelevant. Detecting whether an element is a cursor can be difficult. Since the MNT_CURSOR flag is a preprocessor constant, it's not present in debuginfo, and since its value is repurposed, we cannot hard-code it. For this specific issue, cursors are possible to detect in other ways, but ideally, we would be able to read the mount flag definitions out of the debuginfo. For that reason, convert the mount flags to an enum. Link: https://github.com/osandov/drgn/pull/496 Signed-off-by: Stephen Brennan Link: https://lore.kernel.org/20250507223402.2795029-1-stephen.s.brennan@oracle.com Signed-off-by: Christian Brauner

kill vfs_submount()

2025-05-06T16:49:07Z

The last remaining user of vfs_submount() (tracefs) is easy to convert to fs_context_for_submount(); do that and bury that thing, along with SB_SUBMOUNT Reviewed-by: Jan Kara Acked-by: Steven Rostedt (Google) Tested-by: Steven Rostedt (Google) Signed-off-by: Al Viro

Merge tag 'vfs-6.14-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2025-01-20T17:40:49Z

Pull misc vfs updates from Christian Brauner: "Features: - Support caching symlink lengths in inodes The size is stored in a new union utilizing the same space as i_devices, thus avoiding growing the struct or taking up any more space When utilized it dodges strlen() in vfs_readlink(), giving about 1.5% speed up when issuing readlink on /initrd.img on ext4 - Add RWF_DONTCACHE iocb and FOP_DONTCACHE file_operations flag If a file system supports uncached buffered IO, it may set FOP_DONTCACHE and enable support for RWF_DONTCACHE. If RWF_DONTCACHE is attempted without the file system supporting it, it'll get errored with -EOPNOTSUPP - Enable VBOXGUEST and VBOXSF_FS on ARM64 Now that VirtualBox is able to run as a host on arm64 (e.g. the Apple M3 processors) we can enable VBOXSF_FS (and in turn VBOXGUEST) for this architecture. Tested with various runs of bonnie++ and dbench on an Apple MacBook Pro with the latest Virtualbox 7.1.4 r165100 installed Cleanups: - Delay sysctl_nr_open check in expand_files() - Use kernel-doc includes in fiemap docbook - Use page->private instead of page->index in watch_queue - Use a consume fence in mnt_idmap() as it's heavily used in link_path_walk() - Replace magic number 7 with ARRAY_SIZE() in fc_log - Sort out a stale comment about races between fd alloc and dup2() - Fix return type of do_mount() from long to int - Various cosmetic cleanups for the lockref code Fixes: - Annotate spinning as unlikely() in __read_seqcount_begin The annotation already used to be there, but got lost in commit 52ac39e5db51 ("seqlock: seqcount_t: Implement all read APIs as statement expressions") - Fix proc_handler for sysctl_nr_open - Flush delayed work in delayed fput() - Fix grammar and spelling in propagate_umount() - Fix ESP not readable during coredump In /proc/PID/stat, there is the kstkesp field which is the stack pointer of a thread. While the thread is active, this field reads zero. But during a coredump, it should have a valid value However, at the moment, kstkesp is zero even during coredump - Don't wake up the writer if the pipe is still full - Fix unbalanced user_access_end() in select code" * tag 'vfs-6.14-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (28 commits) gfs2: use lockref_init for qd_lockref erofs: use lockref_init for pcl->lockref dcache: use lockref_init for d_lockref lockref: add a lockref_init helper lockref: drop superfluous externs lockref: use bool for false/true returns lockref: improve the lockref_get_not_zero description lockref: remove lockref_put_not_zero fs: Fix return type of do_mount() from long to int select: Fix unbalanced user_access_end() vbox: Enable VBOXGUEST and VBOXSF_FS on ARM64 pipe_read: don't wake up the writer if the pipe is still full selftests: coredump: Add stackdump test fs/proc: do_task_stat: Fix ESP not readable during coredump fs: add RWF_DONTCACHE iocb and FOP_DONTCACHE file_operations flag fs: sort out a stale comment about races between fd alloc and dup2 fs: Fix grammar and spelling in propagate_umount() fs: fc_log replace magic number 7 with ARRAY_SIZE() fs: use a consume fence in mnt_idmap() file: flush delayed work in delayed fput() ...

fs: Fix return type of do_mount() from long to int

2025-01-16T10:48:06Z

Fix the return type of do_mount() function from long to int to match its ac tual behavior. The function only returns int values, and all callers, inclu ding those in fs/namespace.c and arch/alpha/kernel/osf_sys.c, already treat the return value as int. This change improves type consistency across the filesystem code and aligns the function signature with its existing impleme ntation and usage. Signed-off-by: Sentaro Onizuka Link: https://lore.kernel.org/r/20250113151400.55512-1-sentaro@amazon.com Signed-off-by: Christian Brauner

fs: kill MNT_ONRB

2025-01-09T15:58:50Z

Move mnt->mnt_node into the union with mnt->mnt_rcu and mnt->mnt_llist instead of keeping it with mnt->mnt_list. This allows us to use RB_CLEAR_NODE(&mnt->mnt_node) in umount_tree() as well as list_empty(&mnt->mnt_node). That in turn allows us to remove MNT_ONRB. This also fixes the bug reported in [1] where seemingly MNT_ONRB wasn't set in @mnt->mnt_flags even though the mount was present in the mount rbtree of the mount namespace. The root cause is the following race. When a btrfs subvolume is mounted a temporary mount is created: btrfs_get_tree_subvol() { mnt = fc_mount() // Register the newly allocated mount with sb->mounts: lock_mount_hash(); list_add_tail(&mnt->mnt_instance, &mnt->mnt.mnt_sb->s_mounts); unlock_mount_hash(); } and registered on sb->s_mounts. Later it is added to an anonymous mount namespace via mount_subvol(): -> mount_subvol() -> mount_subtree() -> alloc_mnt_ns() mnt_add_to_ns() vfs_path_lookup() put_mnt_ns() The mnt_add_to_ns() call raises MNT_ONRB in @mnt->mnt_flags. If someone concurrently does a ro remount: reconfigure_super() -> sb_prepare_remount_readonly() { list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) { } all mounts registered in sb->s_mounts are visited and first MNT_WRITE_HOLD is raised, then MNT_READONLY is raised, and finally MNT_WRITE_HOLD is removed again. The flag modification for MNT_WRITE_HOLD/MNT_READONLY and MNT_ONRB race so MNT_ONRB might be lost. Fixes: 2eea9ce4310d ("mounts: keep list of mounts in an rbtree") Cc: # v6.8+ Link: https://lore.kernel.org/r/20241215-vfs-6-14-mount-work-v1-1-fd55922c4af8@kernel.org Link: https://lore.kernel.org/r/ec6784ed-8722-4695-980a-4400d4e7bd1a@gmx.com [1] Signed-off-by: Christian Brauner

fs: use a consume fence in mnt_idmap()

2024-12-22T10:29:52Z

The routine is used in link_path_walk() for every path component. To my reading the entire point of the fence was to grab a fully populated mnt_idmap, but that's already going to happen with mere consume fence. Eliminates an actual fence on arm64. Signed-off-by: Mateusz Guzik Link: https://lore.kernel.org/r/20241130051712.1036527-1-mjguzik@gmail.com Signed-off-by: Christian Brauner