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

Pull bcachefs locking fix from Al Viro:
"Fix broken locking in bch2_ioctl_subvolume_destroy()"

* tag 'pull-bcachefs-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
bch2_ioctl_subvolume_destroy(): fix locking
new helper: user_path_locked_at()

fs/bcachefs/fs-ioctl.c

···
 static long bch2_ioctl_subvolume_destroy(struct bch_fs *c, struct file *filp,
 				struct bch_ioctl_subvolume arg)
 {
+	const char __user *name = (void __user *)(unsigned long)arg.dst_ptr;
 	struct path path;
 	struct inode *dir;
+	struct dentry *victim;
 	int ret = 0;
 
 	if (arg.flags)
 		return -EINVAL;
 
-	ret = user_path_at(arg.dirfd,
-			(const char __user *)(unsigned long)arg.dst_ptr,
-			LOOKUP_FOLLOW, &path);
-	if (ret)
-		return ret;
+	victim = user_path_locked_at(arg.dirfd, name, &path);
+	if (IS_ERR(victim))
+		return PTR_ERR(victim);
 
-	if (path.dentry->d_sb->s_fs_info != c) {
+	if (victim->d_sb->s_fs_info != c) {
 		ret = -EXDEV;
 		goto err;
 	}
-
-	dir = path.dentry->d_parent->d_inode;
-
-	ret = __bch2_unlink(dir, path.dentry, true);
-	if (ret)
+	if (!d_is_positive(victim)) {
+		ret = -ENOENT;
 		goto err;
-
-	fsnotify_rmdir(dir, path.dentry);
-	d_delete(path.dentry);
+	}
+	dir = d_inode(path.dentry);
+	ret = __bch2_unlink(dir, victim, true);
+	if (!ret) {
+		fsnotify_rmdir(dir, victim);
+		d_delete(victim);
+	}
+	inode_unlock(dir);
 err:
+	dput(victim);
 	path_put(&path);
 	return ret;
 }

fs/namei.c

···
 }
 
 /* does lookup, returns the object with parent locked */
-static struct dentry *__kern_path_locked(struct filename *name, struct path *path)
+static struct dentry *__kern_path_locked(int dfd, struct filename *name, struct path *path)
 {
 	struct dentry *d;
 	struct qstr last;
 	int type, error;
 
-	error = filename_parentat(AT_FDCWD, name, 0, path, &last, &type);
+	error = filename_parentat(dfd, name, 0, path, &last, &type);
 	if (error)
 		return ERR_PTR(error);
 	if (unlikely(type != LAST_NORM)) {
···
 struct dentry *kern_path_locked(const char *name, struct path *path)
 {
 	struct filename *filename = getname_kernel(name);
-	struct dentry *res = __kern_path_locked(filename, path);
+	struct dentry *res = __kern_path_locked(AT_FDCWD, filename, path);
 
 	putname(filename);
 	return res;
 }
+
+struct dentry *user_path_locked_at(int dfd, const char __user *name, struct path *path)
+{
+	struct filename *filename = getname(name);
+	struct dentry *res = __kern_path_locked(dfd, filename, path);
+
+	putname(filename);
+	return res;
+}
+EXPORT_SYMBOL(user_path_locked_at);
 
 int kern_path(const char *name, unsigned int flags, struct path *path)
 {

include/linux/namei.h

···
 extern struct dentry *user_path_create(int, const char __user *, struct path *, unsigned int);
 extern void done_path_create(struct path *, struct dentry *);
 extern struct dentry *kern_path_locked(const char *, struct path *);
+extern struct dentry *user_path_locked_at(int , const char __user *, struct path *);
 int vfs_path_parent_lookup(struct filename *filename, unsigned int flags,
 			   struct path *parent, struct qstr *last, int *type,
 			   const struct path *root);