From: Al Viro Date: Tue, 17 Jun 2025 04:09:51 +0000 (-0400) Subject: replace collect_mounts()/drop_collected_mounts() with a safer variant X-Git-Tag: v6.16-rc4~29^2~2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=7484e15dbb016d9d40f8c6e0475810212ae181db;p=thirdparty%2Flinux.git 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 --- diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst index 3616d7161dab..a5734bdd1cc7 100644 --- a/Documentation/filesystems/porting.rst +++ b/Documentation/filesystems/porting.rst @@ -1249,3 +1249,12 @@ Using try_lookup_noperm() will require linux/namei.h to be included. Calling conventions for ->d_automount() have changed; we should *not* grab an extra reference to new mount - it should be returned with refcount 1. + +--- + +collect_mounts()/drop_collected_mounts()/iterate_mounts() are gone now. +Replacement is collect_paths()/drop_collected_path(), with no special +iterator needed. Instead of a cloned mount tree, the new interface returns +an array of struct path, one for each mount collect_mounts() would've +created. These struct path point to locations in the caller's namespace +that would be roots of the cloned mounts. diff --git a/fs/namespace.c b/fs/namespace.c index e13d9ab4f564..14601ec4c2c5 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2310,21 +2310,62 @@ out: return dst_mnt; } -/* Caller should check returned pointer for errors */ +static inline bool extend_array(struct path **res, struct path **to_free, + unsigned n, unsigned *count, unsigned new_count) +{ + struct path *p; + + if (likely(n < *count)) + return true; + p = kmalloc_array(new_count, sizeof(struct path), GFP_KERNEL); + if (p && *count) + memcpy(p, *res, *count * sizeof(struct path)); + *count = new_count; + kfree(*to_free); + *to_free = *res = p; + return p; +} -struct vfsmount *collect_mounts(const struct path *path) +struct path *collect_paths(const struct path *path, + struct path *prealloc, unsigned count) { - struct mount *tree; - namespace_lock(); - if (!check_mnt(real_mount(path->mnt))) - tree = ERR_PTR(-EINVAL); - else - tree = copy_tree(real_mount(path->mnt), path->dentry, - CL_COPY_ALL | CL_PRIVATE); - namespace_unlock(); - if (IS_ERR(tree)) - return ERR_CAST(tree); - return &tree->mnt; + struct mount *root = real_mount(path->mnt); + struct mount *child; + struct path *res = prealloc, *to_free = NULL; + unsigned n = 0; + + guard(rwsem_read)(&namespace_sem); + + if (!check_mnt(root)) + return ERR_PTR(-EINVAL); + if (!extend_array(&res, &to_free, 0, &count, 32)) + return ERR_PTR(-ENOMEM); + res[n++] = *path; + list_for_each_entry(child, &root->mnt_mounts, mnt_child) { + if (!is_subdir(child->mnt_mountpoint, path->dentry)) + continue; + for (struct mount *m = child; m; m = next_mnt(m, child)) { + if (!extend_array(&res, &to_free, n, &count, 2 * count)) + return ERR_PTR(-ENOMEM); + res[n].mnt = &m->mnt; + res[n].dentry = m->mnt.mnt_root; + n++; + } + } + if (!extend_array(&res, &to_free, n, &count, count + 1)) + return ERR_PTR(-ENOMEM); + memset(res + n, 0, (count - n) * sizeof(struct path)); + for (struct path *p = res; p->mnt; p++) + path_get(p); + return res; +} + +void drop_collected_paths(struct path *paths, struct path *prealloc) +{ + for (struct path *p = paths; p->mnt; p++) + path_put(p); + if (paths != prealloc) + kfree(paths); } static void free_mnt_ns(struct mnt_namespace *); @@ -2401,15 +2442,6 @@ void dissolve_on_fput(struct vfsmount *mnt) free_mnt_ns(ns); } -void drop_collected_mounts(struct vfsmount *mnt) -{ - namespace_lock(); - lock_mount_hash(); - umount_tree(real_mount(mnt), 0); - unlock_mount_hash(); - namespace_unlock(); -} - static bool __has_locked_children(struct mount *mnt, struct dentry *dentry) { struct mount *child; @@ -2511,21 +2543,6 @@ struct vfsmount *clone_private_mount(const struct path *path) } EXPORT_SYMBOL_GPL(clone_private_mount); -int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg, - struct vfsmount *root) -{ - struct mount *mnt; - int res = f(root, arg); - if (res) - return res; - list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) { - res = f(&mnt->mnt, arg); - if (res) - return res; - } - return 0; -} - static void lock_mnt_tree(struct mount *mnt) { struct mount *p; @@ -6262,7 +6279,11 @@ void put_mnt_ns(struct mnt_namespace *ns) { if (!refcount_dec_and_test(&ns->ns.count)) return; - drop_collected_mounts(&ns->root->mnt); + namespace_lock(); + lock_mount_hash(); + umount_tree(ns->root, 0); + unlock_mount_hash(); + namespace_unlock(); free_mnt_ns(ns); } diff --git a/fs/pnode.h b/fs/pnode.h index 34b6247af01d..2d026fb98b18 100644 --- a/fs/pnode.h +++ b/fs/pnode.h @@ -28,8 +28,6 @@ #define CL_SHARED_TO_SLAVE 0x20 #define CL_COPY_MNT_NS_FILE 0x40 -#define CL_COPY_ALL (CL_COPY_UNBINDABLE | CL_COPY_MNT_NS_FILE) - static inline void set_mnt_shared(struct mount *mnt) { mnt->mnt.mnt_flags &= ~MNT_SHARED_MASK; 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); diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c index f2f38903b2fe..b0eae2a3c895 100644 --- a/kernel/audit_tree.c +++ b/kernel/audit_tree.c @@ -668,12 +668,6 @@ int audit_remove_tree_rule(struct audit_krule *rule) return 0; } -static int compare_root(struct vfsmount *mnt, void *arg) -{ - return inode_to_key(d_backing_inode(mnt->mnt_root)) == - (unsigned long)arg; -} - void audit_trim_trees(void) { struct list_head cursor; @@ -683,8 +677,9 @@ void audit_trim_trees(void) while (cursor.next != &tree_list) { struct audit_tree *tree; struct path path; - struct vfsmount *root_mnt; struct audit_node *node; + struct path *paths; + struct path array[16]; int err; tree = container_of(cursor.next, struct audit_tree, list); @@ -696,9 +691,9 @@ void audit_trim_trees(void) if (err) goto skip_it; - root_mnt = collect_mounts(&path); + paths = collect_paths(&path, array, 16); path_put(&path); - if (IS_ERR(root_mnt)) + if (IS_ERR(paths)) goto skip_it; spin_lock(&hash_lock); @@ -706,14 +701,17 @@ void audit_trim_trees(void) struct audit_chunk *chunk = find_chunk(node); /* this could be NULL if the watch is dying else where... */ node->index |= 1U<<31; - if (iterate_mounts(compare_root, - (void *)(chunk->key), - root_mnt)) - node->index &= ~(1U<<31); + for (struct path *p = paths; p->dentry; p++) { + struct inode *inode = p->dentry->d_inode; + if (inode_to_key(inode) == chunk->key) { + node->index &= ~(1U<<31); + break; + } + } } spin_unlock(&hash_lock); trim_marked(tree); - drop_collected_mounts(root_mnt); + drop_collected_paths(paths, array); skip_it: put_tree(tree); mutex_lock(&audit_filter_mutex); @@ -742,9 +740,14 @@ void audit_put_tree(struct audit_tree *tree) put_tree(tree); } -static int tag_mount(struct vfsmount *mnt, void *arg) +static int tag_mounts(struct path *paths, struct audit_tree *tree) { - return tag_chunk(d_backing_inode(mnt->mnt_root), arg); + for (struct path *p = paths; p->dentry; p++) { + int err = tag_chunk(p->dentry->d_inode, tree); + if (err) + return err; + } + return 0; } /* @@ -801,7 +804,8 @@ int audit_add_tree_rule(struct audit_krule *rule) { struct audit_tree *seed = rule->tree, *tree; struct path path; - struct vfsmount *mnt; + struct path array[16]; + struct path *paths; int err; rule->tree = NULL; @@ -828,16 +832,16 @@ int audit_add_tree_rule(struct audit_krule *rule) err = kern_path(tree->pathname, 0, &path); if (err) goto Err; - mnt = collect_mounts(&path); + paths = collect_paths(&path, array, 16); path_put(&path); - if (IS_ERR(mnt)) { - err = PTR_ERR(mnt); + if (IS_ERR(paths)) { + err = PTR_ERR(paths); goto Err; } get_tree(tree); - err = iterate_mounts(tag_mount, tree, mnt); - drop_collected_mounts(mnt); + err = tag_mounts(paths, tree); + drop_collected_paths(paths, array); if (!err) { struct audit_node *node; @@ -872,20 +876,21 @@ int audit_tag_tree(char *old, char *new) struct list_head cursor, barrier; int failed = 0; struct path path1, path2; - struct vfsmount *tagged; + struct path array[16]; + struct path *paths; int err; err = kern_path(new, 0, &path2); if (err) return err; - tagged = collect_mounts(&path2); + paths = collect_paths(&path2, array, 16); path_put(&path2); - if (IS_ERR(tagged)) - return PTR_ERR(tagged); + if (IS_ERR(paths)) + return PTR_ERR(paths); err = kern_path(old, 0, &path1); if (err) { - drop_collected_mounts(tagged); + drop_collected_paths(paths, array); return err; } @@ -914,7 +919,7 @@ int audit_tag_tree(char *old, char *new) continue; } - failed = iterate_mounts(tag_mount, tree, tagged); + failed = tag_mounts(paths, tree); if (failed) { put_tree(tree); mutex_lock(&audit_filter_mutex); @@ -955,7 +960,7 @@ int audit_tag_tree(char *old, char *new) list_del(&cursor); mutex_unlock(&audit_filter_mutex); path_put(&path1); - drop_collected_mounts(tagged); + drop_collected_paths(paths, array); return failed; }