From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f194.google.com ([209.85.215.194]:33049 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731156AbeGWCmS (ORCPT ); Sun, 22 Jul 2018 22:42:18 -0400 Received: by mail-pg1-f194.google.com with SMTP id r5-v6so11038056pgv.0 for ; Sun, 22 Jul 2018 18:43:34 -0700 (PDT) Subject: Re: [PATCH net] ip: in cmsg IP(V6)_ORIGDSTADDR do not read beyond headlen To: Willem de Bruijn , netdev@vger.kernel.org Cc: davem@davemloft.net, Willem de Bruijn References: <20180723004345.16886-1-willemdebruijn.kernel@gmail.com> From: Eric Dumazet Message-ID: <2c2c364a-f97c-21e7-1969-c94ca9cb7cbd@gmail.com> Date: Sun, 22 Jul 2018 18:43:31 -0700 MIME-Version: 1.0 In-Reply-To: <20180723004345.16886-1-willemdebruijn.kernel@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org List-ID: On 07/22/2018 05:43 PM, Willem de Bruijn wrote: > From: Willem de Bruijn > > Syzbot reported a read beyond the end of the skb head when returning > IPV6_ORIGDSTADDR: > > BUG: KMSAN: kernel-infoleak in put_cmsg+0x5ef/0x860 net/core/scm.c:242 > CPU: 0 PID: 4501 Comm: syz-executor128 Not tainted 4.17.0+ #9 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x185/0x1d0 lib/dump_stack.c:113 > kmsan_report+0x188/0x2a0 mm/kmsan/kmsan.c:1125 > kmsan_internal_check_memory+0x138/0x1f0 mm/kmsan/kmsan.c:1219 > kmsan_copy_to_user+0x7a/0x160 mm/kmsan/kmsan.c:1261 > copy_to_user include/linux/uaccess.h:184 [inline] > put_cmsg+0x5ef/0x860 net/core/scm.c:242 > ip6_datagram_recv_specific_ctl+0x1cf3/0x1eb0 net/ipv6/datagram.c:719 > ip6_datagram_recv_ctl+0x41c/0x450 net/ipv6/datagram.c:733 > rawv6_recvmsg+0x10fb/0x1460 net/ipv6/raw.c:521 > [..] > > This logic and its ipv4 counterpart read the destination port from > the packet at skb_transport_offset(skb) + 4. > > With MSG_MORE and a local SOCK_RAW sender, syzbot was able to cook a > packet that stores headers exactly up to skb_transport_offset(skb) in > the head and the remainder in a frag. > > Avoid reading beyond skb->tail by testing skb_headlen(skb) instead of > skb->len when trying to access this field. > > Link: http://lkml.kernel.org/r/CAF=yD-LEJwZj5a1-bAAj2Oy_hKmGygV6rsJ_WOrAYnv-fnayiQ@mail.gmail.com > Reported-by: syzbot+9adb4b567003cac781f0@syzkaller.appspotmail.com > Signed-off-by: Willem de Bruijn > --- > net/ipv4/ip_sockglue.c | 2 +- > net/ipv6/datagram.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c > index 64c76dcf7386..5f228d641d9b 100644 > --- a/net/ipv4/ip_sockglue.c > +++ b/net/ipv4/ip_sockglue.c > @@ -152,7 +152,7 @@ static void ip_cmsg_recv_dstaddr(struct msghdr *msg, struct sk_buff *skb) > const struct iphdr *iph = ip_hdr(skb); > __be16 *ports = (__be16 *)skb_transport_header(skb); > > - if (skb_transport_offset(skb) + 4 > (int)skb->len) > + if (skb_transport_offset(skb) + 4 > (int)skb_headlen(skb)) > return; > This really should call pskb_may_pull() or skb_header_pointer().