quota: Fix deadlock during path resolution

As Al Viro pointed out path resolution during Q_QUOTAON calls to quotactl
is prone to deadlocks. We hold s_umount semaphore for reading during the
path resolution and resolution itself may need to acquire the semaphore
for writing when e. g. autofs mountpoint is passed.

Solve the problem by performing the resolution before we get hold of the
superblock (and thus s_umount semaphore). The whole thing is complicated
by the fact that some filesystems (OCFS2) ignore the path argument. So to
distinguish between filesystem which want the path and which do not we
introduce new .quota_on_meta callback which does not get the path. OCFS2
then uses this callback instead of old .quota_on.

CC: Al Viro <viro@ZenIV.linux.org.uk>
CC: Christoph Hellwig <hch@lst.de>
CC: Ted Ts'o <tytso@mit.edu>
CC: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 7 insertions, 18 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 29c80f6d8b2..0f10ccd6bfc 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1162,7 +1162,7 @@ static int ext4_release_dquot(struct dquot *dquot);
 static int ext4_mark_dquot_dirty(struct dquot *dquot);
 static int ext4_write_info(struct super_block *sb, int type);
 static int ext4_quota_on(struct super_block *sb, int type, int format_id,
-				char *path);
+			 struct path *path);
 static int ext4_quota_off(struct super_block *sb, int type);
 static int ext4_quota_on_mount(struct super_block *sb, int type);
 static ssize_t ext4_quota_read(struct super_block *sb, int type, char *data,
@@ -4566,27 +4566,20 @@ static int ext4_quota_on_mount(struct super_block *sb, int type)
  * Standard function to be called on quota_on
  */
 static int ext4_quota_on(struct super_block *sb, int type, int format_id,
-			 char *name)
+			 struct path *path)
 {
 	int err;
-	struct path path;
 
 	if (!test_opt(sb, QUOTA))
 		return -EINVAL;
 
-	err = kern_path(name, LOOKUP_FOLLOW, &path);
-	if (err)
-		return err;
-
 	/* Quotafile not on the same filesystem? */
-	if (path.mnt->mnt_sb != sb) {
-		path_put(&path);
+	if (path->mnt->mnt_sb != sb)
 		return -EXDEV;
-	}
 	/* Journaling quota? */
 	if (EXT4_SB(sb)->s_qf_names[type]) {
 		/* Quotafile not in fs root? */
-		if (path.dentry->d_parent != sb->s_root)
+		if (path->dentry->d_parent != sb->s_root)
 			ext4_msg(sb, KERN_WARNING,
 				"Quota file not on filesystem root. "
 				"Journaled quota will not work");
@@ -4597,7 +4590,7 @@ static int ext4_quota_on(struct super_block *sb, int type, int format_id,
 	 * all updates to the file when we bypass pagecache...
 	 */
 	if (EXT4_SB(sb)->s_journal &&
-	    ext4_should_journal_data(path.dentry->d_inode)) {
+	    ext4_should_journal_data(path->dentry->d_inode)) {
 		/*
 		 * We don't need to lock updates but journal_flush() could
 		 * otherwise be livelocked...
@@ -4605,15 +4598,11 @@ static int ext4_quota_on(struct super_block *sb, int type, int format_id,
 		jbd2_journal_lock_updates(EXT4_SB(sb)->s_journal);
 		err = jbd2_journal_flush(EXT4_SB(sb)->s_journal);
 		jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
-		if (err) {
-			path_put(&path);
+		if (err)
 			return err;
-		}
 	}
 
-	err = dquot_quota_on_path(sb, type, format_id, &path);
-	path_put(&path);
-	return err;
+	return dquot_quota_on(sb, type, format_id, path);
 }
 
 static int ext4_quota_off(struct super_block *sb, int type)