ovl: improve mount helpers

Move common checks into ovl_mount_dir() helper.

Create helper for looking up lower directories.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/overlayfs/super.c

@@ -669,24 +669,6 @@ static void ovl_unescape(char *s)
 	}
 }
 
-static int ovl_mount_dir(const char *name, struct path *path)
-{
-	int err;
-	char *tmp = kstrdup(name, GFP_KERNEL);
-
-	if (!tmp)
-		return -ENOMEM;
-
-	ovl_unescape(tmp);
-	err = kern_path(tmp, LOOKUP_FOLLOW, path);
-	if (err) {
-		pr_err("overlayfs: failed to resolve '%s': %i\n", tmp, err);
-		err = -EINVAL;
-	}
-	kfree(tmp);
-	return err;
-}
-
 static bool ovl_is_allowed_fs_type(struct dentry *root)
 {
 	const struct dentry_operations *dop = root->d_op;
@@ -706,6 +688,71 @@ static bool ovl_is_allowed_fs_type(struct dentry *root)
 	return true;
 }
 
+static int ovl_mount_dir_noesc(const char *name, struct path *path)
+{
+	int err;
+
+	err = kern_path(name, LOOKUP_FOLLOW, path);
+	if (err) {
+		pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
+		goto out;
+	}
+	err = -EINVAL;
+	if (!ovl_is_allowed_fs_type(path->dentry)) {
+		pr_err("overlayfs: filesystem on '%s' not supported\n", name);
+		goto out_put;
+	}
+	if (!S_ISDIR(path->dentry->d_inode->i_mode)) {
+		pr_err("overlayfs: '%s' not a directory\n", name);
+		goto out_put;
+	}
+	return 0;
+
+out_put:
+	path_put(path);
+out:
+	return err;
+}
+
+static int ovl_mount_dir(const char *name, struct path *path)
+{
+	int err = -ENOMEM;
+	char *tmp = kstrdup(name, GFP_KERNEL);
+
+	if (tmp) {
+		ovl_unescape(tmp);
+		err = ovl_mount_dir_noesc(tmp, path);
+		kfree(tmp);
+	}
+	return err;
+}
+
+static int ovl_lower_dir(const char *name, struct path *path, long *namelen,
+			 int *stack_depth)
+{
+	int err;
+	struct kstatfs statfs;
+
+	err = ovl_mount_dir(name, path);
+	if (err)
+		goto out;
+
+	err = vfs_statfs(path, &statfs);
+	if (err) {
+		pr_err("overlayfs: statfs failed on '%s'\n", name);
+		goto out_put;
+	}
+	*namelen = max(*namelen, statfs.f_namelen);
+	*stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
+
+	return 0;
+
+out_put:
+	path_put(path);
+out:
+	return err;
+}
+
 /* Workdir should not be subdir of upperdir and vice versa */
 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
 {
@@ -726,7 +773,6 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	struct dentry *root_dentry;
 	struct ovl_entry *oe;
 	struct ovl_fs *ufs;
-	struct kstatfs statfs;
 	struct vfsmount *mnt;
 	unsigned int i;
 	int err;
@@ -756,48 +802,23 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	if (err)
 		goto out_put_upperpath;
 
-	err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
-	if (err)
-		goto out_put_workpath;
-
-	err = -EINVAL;
-	if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
-	    !S_ISDIR(lowerpath.dentry->d_inode->i_mode) ||
-	    !S_ISDIR(workpath.dentry->d_inode->i_mode)) {
-		pr_err("overlayfs: upperdir or lowerdir or workdir not a directory\n");
-		goto out_put_lowerpath;
-	}
-
 	if (upperpath.mnt != workpath.mnt) {
 		pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
-		goto out_put_lowerpath;
+		goto out_put_workpath;
 	}
 	if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
 		pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
-		goto out_put_lowerpath;
-	}
-
-	if (!ovl_is_allowed_fs_type(upperpath.dentry)) {
-		pr_err("overlayfs: filesystem of upperdir is not supported\n");
-		goto out_put_lowerpath;
-	}
-
-	if (!ovl_is_allowed_fs_type(lowerpath.dentry)) {
-		pr_err("overlayfs: filesystem of lowerdir is not supported\n");
-		goto out_put_lowerpath;
-	}
-
-	err = vfs_statfs(&lowerpath, &statfs);
-	if (err) {
-		pr_err("overlayfs: statfs failed on lowerpath\n");
-		goto out_put_lowerpath;
+		goto out_put_workpath;
 	}
-	ufs->lower_namelen = statfs.f_namelen;
+	sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
 
-	sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
-				lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
+	err = ovl_lower_dir(ufs->config.lowerdir, &lowerpath,
+			    &ufs->lower_namelen, &sb->s_stack_depth);
+	if (err)
+		goto out_put_workpath;
 
 	err = -EINVAL;
+	sb->s_stack_depth++;
 	if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
 		pr_err("overlayfs: maximum fs stacking depth exceeded\n");
 		goto out_put_lowerpath;