ocfs2: update d_splice_alias() return code checking

When commit d3556ba ("ocfs2: fix d_splice_alias() return code
checking") was merged into v3.18-rc3, d_splice_alias() was returning one
of a valid dentry, NULL or an ERR_PTR.

When commit b5ae6b1 ("merge d_materialise_unique() into
d_splice_alias()") was merged into v3.19-rc1, d_splice_alias() started
returning -ELOOP as one of ERR_PTR values.

Now, when syzkaller mounts a crafted ocfs2 filesystem image that hits
d_splice_alias() == -ELOOP case from ocfs2_lookup(), ocfs2_lookup() fails
to handle -ELOOP case and generic_shutdown_super() hits "VFS: Busy inodes
after unmount" message.

Instead of calling ocfs2_dentry_attach_lock() or ocfs2_dentry_attach_gen()
when d_splice_alias() returned an ERR_PTR value, change ocfs2_lookup() to
bail out immediately.

Also, ocfs2_lookup() needs to call dupt() when ocfs2_dentry_attach_lock()
returned an ERR_PTR value.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Tetsuo Handa <[email protected]>
Reported-by: syzbot <[email protected]>
Closes: https://syzkaller.appspot.com/bug?extid=1134d3a5b062e9665a7a
Suggested-by: Al Viro <[email protected]>
Reviewed-by: Joseph Qi <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Tetsuo Handa <[email protected]>
Cc: Junxiao Bi <[email protected]>
Cc: Changwei Ge <[email protected]>
Cc: Jun Piao <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Tetsuo Handa

fs/ocfs2/namei.c

@@ -142,6 +142,8 @@ static struct dentry *ocfs2_lookup(struct inode *dir, struct dentry *dentry,
 
 bail_add:
 	ret = d_splice_alias(inode, dentry);
+	if (IS_ERR(ret))
+		goto bail_unlock;
 
 	if (inode) {
 		/*
@@ -154,15 +156,16 @@ static struct dentry *ocfs2_lookup(struct inode *dir, struct dentry *dentry,
 		 * NOTE: This dentry already has ->d_op set from
 		 * ocfs2_get_parent() and ocfs2_get_dentry()
 		 */
-		if (!IS_ERR_OR_NULL(ret))
+		if (ret)
 			dentry = ret;
 
 		status = ocfs2_dentry_attach_lock(dentry, inode,
 						  OCFS2_I(dir)->ip_blkno);
 		if (status) {
 			mlog_errno(status);
+			if (ret)
+				dput(ret);
 			ret = ERR_PTR(status);
-			goto bail_unlock;
 		}
 	} else
 		ocfs2_dentry_attach_gen(dentry);