From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean Sacren Subject: Re: [PATCH net] net: ipv6: tcp: fix potential use after free in tcp_v6_do_rcv Date: Tue, 3 Sep 2013 13:46:20 -0600 Message-ID: <20130903194620.GE8262@mail.gmail.com> References: <1378229352-9779-1-git-send-email-dborkman@redhat.com> <1378230513.7360.37.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Daniel Borkmann , davem@davemloft.net, netdev@vger.kernel.org, yoshfuji@linux-ipv6.org To: Eric Dumazet Return-path: Received: from mail-pd0-f173.google.com ([209.85.192.173]:64246 "EHLO mail-pd0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753265Ab3ICTsq (ORCPT ); Tue, 3 Sep 2013 15:48:46 -0400 Received: by mail-pd0-f173.google.com with SMTP id p10so6439094pdj.4 for ; Tue, 03 Sep 2013 12:48:45 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1378230513.7360.37.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Date: Tue, 03 Sep 2013 10:48:33 -0700 > > On Tue, 2013-09-03 at 19:29 +0200, Daniel Borkmann wrote: > > In tcp_v6_do_rcv() code, when processing pkt options, we soley work > > on our skb clone opt_skb that we've created earlier before entering > > tcp_rcv_established() on our way. However, only in condition ... > > > > if (np->rxopt.bits.rxtclass) > > np->rcv_tclass = ipv6_get_dsfield(ipv6_hdr(skb)); > > > > ... we work on skb itself. As we extract every other information out > > of opt_skb in ipv6_pktoptions path, this seems wrong, since skb can > > already be released by tcp_rcv_established() earlier on. When we try > > to access it in ipv6_hdr(), we will dereference freed skb. > > > > Signed-off-by: Daniel Borkmann > > Cc: Eric Dumazet > > --- > > net/ipv6/tcp_ipv6.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c > > index 6e1649d..eeb4cb0 100644 > > --- a/net/ipv6/tcp_ipv6.c > > +++ b/net/ipv6/tcp_ipv6.c > > @@ -1427,7 +1427,7 @@ ipv6_pktoptions: > > if (np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) > > np->mcast_hops = ipv6_hdr(opt_skb)->hop_limit; > > if (np->rxopt.bits.rxtclass) > > - np->rcv_tclass = ipv6_get_dsfield(ipv6_hdr(skb)); > > + np->rcv_tclass = ipv6_get_dsfield(ipv6_hdr(opt_skb)); > > if (ipv6_opt_accepted(sk, opt_skb)) { > > skb_set_owner_r(opt_skb, sk); > > opt_skb = xchg(&np->pktoptions, opt_skb); > > Bug added in commit 4c507d2897bd9b > ("net: implement IP_RECVTOS for IP_PKTOPTIONS") > > CC Jiri > > Acked-by: Eric Dumazet You made a mistake. It was introduced in commit e7219858a ("ipv6: Use ipv6_get_dsfield() instead of ipv6_tclass()"). Cc the right party. -- Jean Sacren