From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net] net: ipv6: tcp: fix potential use after free in tcp_v6_do_rcv Date: Tue, 03 Sep 2013 10:48:33 -0700 Message-ID: <1378230513.7360.37.camel@edumazet-glaptop> References: <1378229352-9779-1-git-send-email-dborkman@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, netdev@vger.kernel.org, Jiri Benc To: Daniel Borkmann Return-path: Received: from mail-pa0-f45.google.com ([209.85.220.45]:54715 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753910Ab3ICRsf (ORCPT ); Tue, 3 Sep 2013 13:48:35 -0400 Received: by mail-pa0-f45.google.com with SMTP id bg4so6716902pad.18 for ; Tue, 03 Sep 2013 10:48:35 -0700 (PDT) In-Reply-To: <1378229352-9779-1-git-send-email-dborkman@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: 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