Patch "net: fix keepalive code vs TCP_FASTOPEN_CONNECT" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

net: fix keepalive code vs TCP_FASTOPEN_CONNECT

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-fix-keepalive-code-vs-tcp_fastopen_connect.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Wed, 2 Aug 2017 23:10:46 -0700
Subject: net: fix keepalive code vs TCP_FASTOPEN_CONNECT

From: Eric Dumazet <[email protected]>

[ Upstream commit 2dda640040876cd8ae646408b69eea40c24f9ae9 ]

syzkaller was able to trigger a divide by 0 in TCP stack [1]

Issue here is that keepalive timer needs to be updated to not attempt to send a probe if the connection setup was deferred using TCP_FASTOPEN_CONNECT socket option added in linux-4.11

[1]
divide error: 0000 [#1] SMP

 CPU: 18 PID: 0 Comm: swapper/18 Not tainted
 task: ffff986f62f4b040 ti: ffff986f62fa2000 task.ti: ffff986f62fa2000
 RIP: 0010:[<ffffffff8409cc0d>]  [<ffffffff8409cc0d>] __tcp_select_window+0x8d/0x160
 Call Trace:
  <IRQ>
  [<ffffffff8409d951>] tcp_transmit_skb+0x11/0x20
  [<ffffffff8409da21>] tcp_xmit_probe_skb+0xc1/0xe0
  [<ffffffff840a0ee8>] tcp_write_wakeup+0x68/0x160
  [<ffffffff840a151b>] tcp_keepalive_timer+0x17b/0x230
  [<ffffffff83b3f799>] call_timer_fn+0x39/0xf0
  [<ffffffff83b40797>] run_timer_softirq+0x1d7/0x280
  [<ffffffff83a04ddb>] __do_softirq+0xcb/0x257
  [<ffffffff83ae03ac>] irq_exit+0x9c/0xb0
  [<ffffffff83a04c1a>] smp_apic_timer_interrupt+0x6a/0x80
  [<ffffffff83a03eaf>] apic_timer_interrupt+0x7f/0x90
  <EOI>
  [<ffffffff83fed2ea>] ? cpuidle_enter_state+0x13a/0x3b0
  [<ffffffff83fed2cd>] ? cpuidle_enter_state+0x11d/0x3b0

Tested:

Following packetdrill no longer crashes the kernel

echo 0 >/proc/sys/net/ipv4/tcp_timestamps

// Cache warmup: send a Fast Open cookie request

    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3

+0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+0 setsockopt(3, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0
+0 connect(3, ..., ...) = -1 EINPROGRESS (Operation is now in progress)
+0 > S 0:0(0) <mss 1460,nop,nop,sackOK,nop,wscale 8,FO,nop,nop>
+.01 < S. 123:123(0) ack 1 win 14600 <mss 1460,nop,nop,sackOK,nop,wscale 6,FO abcd1234,nop,nop>
+0 > . 1:1(0) ack 1
+0 close(3) = 0
+0 > F. 1:1(0) ack 1
+0 < F. 1:1(0) ack 2 win 92
+0 > . 2:2(0) ack 2

+0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 4
+0 fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+0 setsockopt(4, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0 +0 setsockopt(4, SOL_SOCKET, SO_KEEPALIVE, [1], 4) = 0
+.01 connect(4, ..., ...) = 0
+0 setsockopt(4, SOL_TCP, TCP_KEEPIDLE, [5], 4) = 0 +10 close(4) = 0

echo 1 >/proc/sys/net/ipv4/tcp_timestamps

---
 net/ipv4/tcp_timer.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -654,7 +654,8 @@ static void tcp_keepalive_timer (unsigne
 		goto death;
 	}
 
-	if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
+	if (!sock_flag(sk, SOCK_KEEPOPEN) ||
+	    ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))
 		goto out;
 
 	elapsed = keepalive_time_when(tp);

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/tcp-avoid-setting-cwnd-to-invalid-ssthresh-after-cwnd-reduction-states.patch queue-4.12/tcp-fastopen-tcp_connect-must-refresh-the-route.patch queue-4.12/net-fix-keepalive-code-vs-tcp_fastopen_connect.patch