Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933210AbcJLNA3 (ORCPT ); Wed, 12 Oct 2016 09:00:29 -0400 Received: from mail.kernel.org ([198.145.29.136]:48398 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932806AbcJLMoo (ORCPT ); Wed, 12 Oct 2016 08:44:44 -0400 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Herbert Xu , "David S. Miller" , Ben Hutchings , Zefan Li Subject: [PATCH 3.4 113/125] net: Fix skb csum races when peeking Date: Wed, 12 Oct 2016 20:33:49 +0800 Message-Id: <1476275641-4697-113-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1476275600-4626-1-git-send-email-lizf@kernel.org> References: <1476275600-4626-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1570 Lines: 46 From: Herbert Xu 3.4.113-rc1 review patch. If anyone has any objections, please let me know. ------------------ [ 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 Signed-off-by: Zefan Li --- net/core/datagram.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/core/datagram.c b/net/core/datagram.c index ba96ad9..bc412ca 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -695,7 +695,8 @@ __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len) 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; } -- 1.9.1