Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755451AbcKNCMz (ORCPT ); Sun, 13 Nov 2016 21:12:55 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:45177 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754591AbcKNCGR (ORCPT ); Sun, 13 Nov 2016 21:06:17 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Cong Wang" , "Yuchung Cheng" , "Neal Cardwell" , "Ilpo =?UTF-8?Q?J=C3=A4rvinen?=" , "Marco Grassi" , "Eric Dumazet" , "David S. Miller" Date: Mon, 14 Nov 2016 00:14:07 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 073/152] tcp: fix use after free in tcp_xmit_retransmit_queue() In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1865 Lines: 51 3.2.84-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet commit bb1fceca22492109be12640d49f5ea5a544c6bb4 upstream. 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 Signed-off-by: Ben Hutchings --- include/net/tcp.h | 2 ++ 1 file changed, 2 insertions(+) --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1293,6 +1293,8 @@ static inline void tcp_check_send_head(s { 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)