From 7484e15dbb016d9d40f8c6e0475810212ae181db Mon Sep 17 00:00:00 2001 From: Al Viro Date: Tue, 17 Jun 2025 00:09:51 -0400 Subject: replace collect_mounts()/drop_collected_mounts() with a safer variant 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 --- include/linux/mount.h | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) (limited to 'include/linux') diff --git a/include/linux/mount.h b/include/linux/mount.h index 4880f434c021..1a508beba446 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -116,10 +116,8 @@ extern int may_umount_tree(struct vfsmount *); extern int may_umount(struct vfsmount *); int do_mount(const char *, const char __user *, const char *, unsigned long, void *); -extern struct vfsmount *collect_mounts(const struct path *); -extern void drop_collected_mounts(struct vfsmount *); -extern int iterate_mounts(int (*)(struct vfsmount *, void *), void *, - struct vfsmount *); +extern struct path *collect_paths(const struct path *, struct path *, unsigned); +extern void drop_collected_paths(struct path *, struct path *); extern void kern_unmount_array(struct vfsmount *mnt[], unsigned int num); extern int cifs_root_data(char **dev, char **opts); -- cgit v1.2.3