[PATCH] fix races and leaks in vfs_quota_on() users

* new helper: vfs_quota_on_path(); equivalent of vfs_quota_on() sans the
  pathname resolution.
* callers of vfs_quota_on() that do their own pathname resolution and
  checks based on it are switched to vfs_quota_on_path(); that way we
  avoid the races.
* reiserfs leaked dentry/vfsmount references on several failure exits.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/dquot.c

@@ -1793,6 +1793,21 @@ static int vfs_quota_on_remount(struct super_block *sb, int type)
 	return ret;
 }
 
+int vfs_quota_on_path(struct super_block *sb, int type, int format_id,
+		      struct path *path)
+{
+	int error = security_quota_on(path->dentry);
+	if (error)
+		return error;
+	/* Quota file not on the same filesystem? */
+	if (path->mnt->mnt_sb != sb)
+		error = -EXDEV;
+	else
+		error = vfs_quota_on_inode(path->dentry->d_inode, type,
+					   format_id);
+	return error;
+}
+
 /* Actual function called from quotactl() */
 int vfs_quota_on(struct super_block *sb, int type, int format_id, char *path,
 		 int remount)
@@ -1804,19 +1819,10 @@ int vfs_quota_on(struct super_block *sb, int type, int format_id, char *path,
 		return vfs_quota_on_remount(sb, type);
 
 	error = path_lookup(path, LOOKUP_FOLLOW, &nd);
-	if (error < 0)
-		return error;
-	error = security_quota_on(nd.path.dentry);
-	if (error)
-		goto out_path;
-	/* Quota file not on the same filesystem? */
-	if (nd.path.mnt->mnt_sb != sb)
-		error = -EXDEV;
-	else
-		error = vfs_quota_on_inode(nd.path.dentry->d_inode, type,
-					   format_id);
-out_path:
+	if (!error) {
+		error = vfs_quota_on_path(sb, type, format_id, &nd.path);
 		path_put(&nd.path);
+	}
 	return error;
 }
 
@@ -2185,6 +2191,7 @@ EXPORT_SYMBOL(unregister_quota_format);
 EXPORT_SYMBOL(dqstats);
 EXPORT_SYMBOL(dq_data_lock);
 EXPORT_SYMBOL(vfs_quota_on);
+EXPORT_SYMBOL(vfs_quota_on_path);
 EXPORT_SYMBOL(vfs_quota_on_mount);
 EXPORT_SYMBOL(vfs_quota_off);
 EXPORT_SYMBOL(vfs_quota_sync);

fs/ext3/super.c

@@ -2810,8 +2810,9 @@ static int ext3_quota_on(struct super_block *sb, int type, int format_id,
 		journal_unlock_updates(EXT3_SB(sb)->s_journal);
 	}
 
+	err = vfs_quota_on_path(sb, type, format_id, &nd.path);
 	path_put(&nd.path);
-	return vfs_quota_on(sb, type, format_id, path, remount);
+	return err;
 }
 
 /* Read data from quotafile - avoid pagecache and such because we cannot afford

fs/ext4/super.c

@@ -3352,8 +3352,9 @@ static int ext4_quota_on(struct super_block *sb, int type, int format_id,
 		jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
 	}
 
+	err = vfs_quota_on_path(sb, type, format_id, &nd.path);
 	path_put(&nd.path);
-	return vfs_quota_on(sb, type, format_id, path, remount);
+	return err;
 }
 
 /* Read data from quotafile - avoid pagecache and such because we cannot afford

fs/reiserfs/super.c

@@ -2076,8 +2076,8 @@ static int reiserfs_quota_on(struct super_block *sb, int type, int format_id,
 		return err;
 	/* Quotafile not on the same filesystem? */
 	if (nd.path.mnt->mnt_sb != sb) {
-		path_put(&nd.path);
-		return -EXDEV;
+		err = -EXDEV;
+		goto out;
 	}
 	inode = nd.path.dentry->d_inode;
 	/* We must not pack tails for quota files on reiserfs for quota IO to work */
@@ -2087,8 +2087,8 @@ static int reiserfs_quota_on(struct super_block *sb, int type, int format_id,
 			reiserfs_warning(sb,
 				"reiserfs: Unpacking tail of quota file failed"
 				" (%d). Cannot turn on quotas.", err);
-			path_put(&nd.path);
-			return -EINVAL;
+			err = -EINVAL;
+			goto out;
 		}
 		mark_inode_dirty(inode);
 	}
@@ -2109,13 +2109,15 @@ static int reiserfs_quota_on(struct super_block *sb, int type, int format_id,
 		/* Just start temporary transaction and finish it */
 		err = journal_begin(&th, sb, 1);
 		if (err)
-			return err;
+			goto out;
 		err = journal_end_sync(&th, sb, 1);
 		if (err)
-			return err;
+			goto out;
 	}
+	err = vfs_quota_on_path(sb, type, format_id, &nd.path);
+out:
 	path_put(&nd.path);
-	return vfs_quota_on(sb, type, format_id, path, 0);
+	return err;
 }
 
 /* Read data from quotafile - avoid pagecache and such because we cannot afford

include/linux/quotaops.h

@@ -43,6 +43,8 @@ int dquot_mark_dquot_dirty(struct dquot *dquot);
 
 int vfs_quota_on(struct super_block *sb, int type, int format_id,
  	char *path, int remount);
+int vfs_quota_on_path(struct super_block *sb, int type, int format_id,
+ 	struct path *path);
 int vfs_quota_on_mount(struct super_block *sb, char *qf_name,
  	int format_id, int type);
 int vfs_quota_off(struct super_block *sb, int type, int remount);