affs_lookup(): close a race with affs_remove_link()

BugLink: https://bugs.launchpad.net/bugs/1775771

commit 30da870c upstream.

we unlock the directory hash too early - if we are looking at secondary
link and primary (in another directory) gets removed just as we unlock,
we could have the old primary moved in place of the secondary, leaving
us to look into freed entry (and leaving our dentry with ->d_fsdata
pointing to a freed entry).

Cc: stable@vger.kernel.org # 2.4.4+
Acked-by: David Sterba <dsterba@suse.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

fs/affs/namei.c

@@ -224,9 +224,10 @@ affs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 
 	affs_lock_dir(dir);
 	bh = affs_find_entry(dir, dentry);
-	affs_unlock_dir(dir);
-	if (IS_ERR(bh))
+	if (IS_ERR(bh)) {
+		affs_unlock_dir(dir);
 		return ERR_CAST(bh);
+	}
 	if (bh) {
 		u32 ino = bh->b_blocknr;
 
@@ -240,10 +241,13 @@ affs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
 		}
 		affs_brelse(bh);
 		inode = affs_iget(sb, ino);
-		if (IS_ERR(inode))
+		if (IS_ERR(inode)) {
+			affs_unlock_dir(dir);
 			return ERR_CAST(inode);
+		}
 	}
 	d_add(dentry, inode);
+	affs_unlock_dir(dir);
 	return NULL;
 }