From mboxrd@z Thu Jan 1 00:00:00 1970 From: Herbert Xu Subject: net: Fix skb csum races when peeking Date: Mon, 13 Jul 2015 20:01:42 +0800 Message-ID: <20150713120142.GA9787@gondor.apana.org.au> References: <20150710115141.12980.88829.stgit@buzz> <20150713072352.GA8485@gondor.apana.org.au> <1436774742.9402.3.camel@edumazet-glaptop2.roam.corp.google.com> <20150713081040.GB8971@gondor.apana.org.au> <1436775754.9402.6.camel@edumazet-glaptop2.roam.corp.google.com> <20150713082544.GA9176@gondor.apana.org.au> <20150713083100.GA9263@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Dumazet , Konstantin Khlebnikov , netdev , "David S. Miller" To: Eric Dumazet Return-path: Received: from helcar.hengli.com.au ([209.40.204.226]:32859 "EHLO helcar.hengli.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751297AbbGMMBw (ORCPT ); Mon, 13 Jul 2015 08:01:52 -0400 Content-Disposition: inline In-Reply-To: <20150713083100.GA9263@gondor.apana.org.au> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Jul 13, 2015 at 04:31:00PM +0800, Herbert Xu wrote: > On Mon, Jul 13, 2015 at 10:28:19AM +0200, Eric Dumazet wrote: > > > > Except that udp checksum are checked outside of spinlock protection. > > Good point. I wonder when this got broken. I'll do some digging. OK looks like I can claim credit for this bug too :) commit fb286bb2990a107009dbf25f6ffebeb7df77f9be Author: Herbert Xu Date: Thu Nov 10 13:01:24 2005 -0800 [NET]: Detect hardware rx checksum faults correctly Although others have made the hole bigger more recently. PS we seem to no longer use the hardware checksum in case of CHECKSUM_COMPLETE, I wonder why that is? ---8<--- 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 diff --git a/net/core/datagram.c b/net/core/datagram.c index b80fb91..4967262 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -622,7 +657,8 @@ __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len) !skb->csum_complete_sw) netdev_rx_csum_fault(skb->dev); } - skb->csum_valid = !sum; + if (!skb_shared(skb)) + skb->csum_valid = !sum; return sum; } EXPORT_SYMBOL(__skb_checksum_complete_head); @@ -642,11 +678,13 @@ __sum16 __skb_checksum_complete(struct sk_buff *skb) netdev_rx_csum_fault(skb->dev); } - /* Save full packet checksum */ - skb->csum = csum; - skb->ip_summed = CHECKSUM_COMPLETE; - skb->csum_complete_sw = 1; - skb->csum_valid = !sum; + if (!skb_shared(skb)) { + /* Save full packet checksum */ + skb->csum = csum; + skb->ip_summed = CHECKSUM_COMPLETE; + skb->csum_complete_sw = 1; + skb->csum_valid = !sum; + } return sum; } -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt