From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konstantin Khlebnikov Subject: [PATCH] netlink: enable skb header refcounting before sending first broadcast Date: Fri, 10 Jul 2015 14:51:41 +0300 Message-ID: <20150710115141.12980.88829.stgit@buzz> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: Eric Dumazet , Herbert Xu To: netdev@vger.kernel.org, "David S. Miller" Return-path: Received: from forward-corp1m.cmail.yandex.net ([5.255.216.100]:49501 "EHLO forward-corp1m.cmail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754208AbbGJLvq (ORCPT ); Fri, 10 Jul 2015 07:51:46 -0400 Sender: netdev-owner@vger.kernel.org List-ID: This fixes race between non-atomic updates of adjacent bit-fields: skb->cloned could be lost because netlink broadcast clones skb after sending it to the first listener who sets skb->peeked at the same skb. As a result atomic refcounting of skb header stays disabled and skb_release_data() frees it twice. Race leads to double-free in kmalloc-xxx. Signed-off-by: Konstantin Khlebnikov Fixes: b19372273164 ("net: reorganize sk_buff for faster __copy_skb_header()") --- net/netlink/af_netlink.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index dea925388a5b..921e0d8dfe3a 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2028,6 +2028,12 @@ int netlink_broadcast_filtered(struct sock *ssk, struct sk_buff *skb, u32 portid info.tx_filter = filter; info.tx_data = filter_data; + /* Enable atomic refcounting in skb_release_data() before first send: + * non-atomic set of that bit-field in __skb_clone() could race with + * __skb_recv_datagram() which touches the same set of bit-fields. + */ + skb->cloned = 1; + /* While we sleep in clone, do not allow to change socket list */ netlink_lock_table();