From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759992AbbJIAVI (ORCPT ); Thu, 8 Oct 2015 20:21:08 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:35475 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758989AbbJIARd (ORCPT ); Thu, 8 Oct 2015 20:17:33 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Eric Dumazet" , "David S. Miller" , "Herbert Xu" Date: Fri, 09 Oct 2015 01:12:28 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 097/107] net: Fix skb csum races when peeking In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.247 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.72-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Herbert Xu [ Upstream commit 89c22d8c3b278212eef6a8cc66b570bc840a6f5a ] When we calculate the checksum on the recv path, we store the result in the skb as an optimisation in case we need the checksum again down the line. This is in fact bogus for the MSG_PEEK case as this is done without any locking. So multiple threads can peek and then store the result to the same skb, potentially resulting in bogus skb states. This patch fixes this by only storing the result if the skb is not shared. This preserves the optimisations for the few cases where it can be done safely due to locking or other reasons, e.g., SIOCINQ. Signed-off-by: Herbert Xu Acked-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/core/datagram.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -691,7 +691,8 @@ __sum16 __skb_checksum_complete_head(str if (likely(!sum)) { if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE)) netdev_rx_csum_fault(skb->dev); - skb->ip_summed = CHECKSUM_UNNECESSARY; + if (!skb_shared(skb)) + skb->ip_summed = CHECKSUM_UNNECESSARY; } return sum; }