From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net v2] af-unix: fix use-after-free with concurrent readers while splicing Date: Tue, 10 Nov 2015 07:18:44 -0800 Message-ID: <1447168724.17135.73.camel@edumazet-glaptop2.roam.corp.google.com> References: <1447166859-11766-1-git-send-email-hannes@stressinduktion.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Dmitry Vyukov To: Hannes Frederic Sowa Return-path: Received: from mail-pa0-f54.google.com ([209.85.220.54]:34176 "EHLO mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752071AbbKJPSr (ORCPT ); Tue, 10 Nov 2015 10:18:47 -0500 Received: by padhx2 with SMTP id hx2so228568600pad.1 for ; Tue, 10 Nov 2015 07:18:47 -0800 (PST) In-Reply-To: <1447166859-11766-1-git-send-email-hannes@stressinduktion.org> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2015-11-10 at 15:47 +0100, Hannes Frederic Sowa wrote: > During splicing an af-unix socket to a pipe we have to drop all > af-unix socket locks. While doing so we allow another reader to enter > unix_stream_read_generic which can read, copy and finally free another > skb. If exactly this skb is just in process of being spliced we get a > use-after-free report by kasan. > > First, we must make sure to not have a free while the skb is used during > the splice operation. We simply increment its use counter before unlocking > the reader lock. > > Stream sockets have the nice characteristic that we don't care about > zero length writes and they never reach the peer socket's queue. That > said, we can take the UNIXCB.consumed field as the indicator if the > skb was already freed from the socket's receive queue. If the skb was > fully consumed after we locked the reader side again we know it has been > dropped by a second reader. We indicate a short read to user space and > abort the current splice operation. > > This bug has been found with syzkaller > (http://github.com/google/syzkaller) by Dmitry Vyukov. > > Reported-by: Dmitry Vyukov > Cc: Dmitry Vyukov > Cc: Eric Dumazet > Signed-off-by: Hannes Frederic Sowa Please Hannes include the Fixes: tag. As you might already know, patchwork does not catch it later Fixes: 2b514574f7e8 ("net: af_unix: implement splice for stream af_unix sockets") Acked-by: Eric Dumazet Also I would prefer skb_get() being on a separate line, to ease future understanding of the code. Thanks.