squashfs: fix name reading in squashfs_xattr_get

Only read potentially matching names into the target buffer, all
obviously non matching names don't need to be read into the
target buffer.

Signed-off-by: Phillip Lougher <[e-mail]>

fs/squashfs/xattr.c

···
 		type = le16_to_cpu(entry.type);
 		prefix = type & SQUASHFS_XATTR_PREFIX_MASK;
 
-		err = squashfs_read_metadata(sb, target, &start, &offset,
-							name_size);
+		if (prefix == name_index && name_size == name_len)
+			err = squashfs_read_metadata(sb, target, &start,
+						&offset, name_size);
+		else
+			err = squashfs_read_metadata(sb, NULL, &start,
+						&offset, name_size);
 		if (err < 0)
 			goto failed;