From patchwork Mon Sep 19 10:11:01 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Luis Henriques X-Patchwork-Id: 671653 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id 3sd1r21JZzz9ryv; Mon, 19 Sep 2016 20:11:14 +1000 (AEST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1blvXX-000065-0C; Mon, 19 Sep 2016 10:11:07 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1blvXS-00005F-SR for kernel-team@lists.ubuntu.com; Mon, 19 Sep 2016 10:11:02 +0000 Received: from 1.general.henrix.uk.vpn ([10.172.192.212] helo=localhost) by youngberry.canonical.com with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.76) (envelope-from ) id 1blvXS-0002dj-GF for kernel-team@lists.ubuntu.com; Mon, 19 Sep 2016 10:11:02 +0000 From: Luis Henriques To: kernel-team@lists.ubuntu.com Subject: [CVE-2016-6828][xenial, vivid, trusty, precise] tcp: fix use after free in tcp_xmit_retransmit_queue() Date: Mon, 19 Sep 2016 11:11:01 +0100 Message-Id: <1474279861-8953-1-git-send-email-luis.henriques@canonical.com> MIME-Version: 1.0 X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com From: Eric Dumazet When tcp_sendmsg() allocates a fresh and empty skb, it puts it at the tail of the write queue using tcp_add_write_queue_tail() Then it attempts to copy user data into this fresh skb. If the copy fails, we undo the work and remove the fresh skb. Unfortunately, this undo lacks the change done to tp->highest_sack and we can leave a dangling pointer (to a freed skb) Later, tcp_xmit_retransmit_queue() can dereference this pointer and access freed memory. For regular kernels where memory is not unmapped, this might cause SACK bugs because tcp_highest_sack_seq() is buggy, returning garbage instead of tp->snd_nxt, but with various debug features like CONFIG_DEBUG_PAGEALLOC, this can crash the kernel. This bug was found by Marco Grassi thanks to syzkaller. Fixes: 6859d49475d4 ("[TCP]: Abstract tp->highest_sack accessing & point to next skb") Reported-by: Marco Grassi Signed-off-by: Eric Dumazet Cc: Ilpo Järvinen Cc: Yuchung Cheng Cc: Neal Cardwell Acked-by: Neal Cardwell Reviewed-by: Cong Wang Signed-off-by: David S. Miller CVE-2016-6828 (cherry picked from commit bb1fceca22492109be12640d49f5ea5a544c6bb4) Signed-off-by: Luis Henriques --- include/net/tcp.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/net/tcp.h b/include/net/tcp.h index 414d822bc1db..9c3ab544d3a8 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1510,6 +1510,8 @@ static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unli { if (sk->sk_send_head == skb_unlinked) sk->sk_send_head = NULL; + if (tcp_sk(sk)->highest_sack == skb_unlinked) + tcp_sk(sk)->highest_sack = NULL; } static inline void tcp_init_send_head(struct sock *sk)