From 5924f17a8a30c2ae18d034a86ee7581b34accef6 Mon Sep 17 00:00:00 2001 From: Christoph Paasch Date: Sat, 28 Jun 2014 18:26:37 +0200 Subject: [PATCH] tcp: Fix divide by zero when pushing during tcp-repair When in repair-mode and TCP_RECV_QUEUE is set, we end up calling tcp_push with mss_now being 0. If data is in the send-queue and tcp_set_skb_tso_segs gets called, we crash because it will divide by mss_now: [ 347.151939] divide error: 0000 [#1] SMP [ 347.152907] Modules linked in: [ 347.152907] CPU: 1 PID: 1123 Comm: packetdrill Not tainted 3.16.0-rc2 #4 [ 347.152907] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007 [ 347.152907] task: f5b88540 ti: f3c82000 task.ti: f3c82000 [ 347.152907] EIP: 0060:[] EFLAGS: 00210246 CPU: 1 [ 347.152907] EIP is at tcp_set_skb_tso_segs+0x49/0xa0 [ 347.152907] EAX: 00000b67 EBX: f5acd080 ECX: 00000000 EDX: 00000000 [ 347.152907] ESI: f5a28f40 EDI: f3c88f00 EBP: f3c83d10 ESP: f3c83d00 [ 347.152907] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 [ 347.152907] CR0: 80050033 CR2: 083158b0 CR3: 35146000 CR4: 000006b0 [ 347.152907] Stack: [ 347.152907] c167f9d9 f5acd080 000005b4 00000002 f3c83d20 c16013e6 f3c88f00 f5acd080 [ 347.152907] f3c83da0 c1603b5a f3c83d38 c10a0188 00000000 00000000 f3c83d84 c10acc85 [ 347.152907] c1ad5ec0 00000000 00000000 c1ad679c 010003e0 00000000 00000000 f3c88fc8 [ 347.152907] Call Trace: [ 347.152907] [] ? apic_timer_interrupt+0x2d/0x34 [ 347.152907] [] tcp_init_tso_segs+0x36/0x50 [ 347.152907] [] tcp_write_xmit+0x7a/0xbf0 [ 347.152907] [] ? up+0x28/0x40 [ 347.152907] [] ? console_unlock+0x295/0x480 [ 347.152907] [] ? vprintk_emit+0x1ef/0x4b0 [ 347.152907] [] __tcp_push_pending_frames+0x36/0xd0 [ 347.152907] [] tcp_push+0xf0/0x120 [ 347.152907] [] tcp_sendmsg+0xf1/0xbf0 [ 347.152907] [] ? kmem_cache_free+0xf0/0x120 [ 347.152907] [] ? __sigqueue_free+0x32/0x40 [ 347.152907] [] ? __sigqueue_free+0x32/0x40 [ 347.152907] [] ? do_wp_page+0x3e0/0x850 [ 347.152907] [] inet_sendmsg+0x4a/0xb0 [ 347.152907] [] ? handle_mm_fault+0x709/0xfb0 [ 347.152907] [] sock_aio_write+0xbb/0xd0 [ 347.152907] [] do_sync_write+0x69/0xa0 [ 347.152907] [] vfs_write+0x123/0x160 [ 347.152907] [] SyS_write+0x55/0xb0 [ 347.152907] [] sysenter_do_call+0x12/0x28 This can easily be reproduced with the following packetdrill-script (the "magic" with netem, sk_pacing and limit_output_bytes is done to prevent the kernel from pushing all segments, because hitting the limit without doing this is not so easy with packetdrill): 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1) = 0 +0 < S 0:0(0) win 32792 +0 > S. 0:0(0) ack 1 +0.1 < . 1:1(0) ack 1 win 65000 +0 accept(3, ..., ...) = 4 // This forces that not all segments of the snd-queue will be pushed +0 `tc qdisc add dev tun0 root netem delay 10ms` +0 `sysctl -w net.ipv4.tcp_limit_output_bytes=2` +0 setsockopt(4, SOL_SOCKET, 47, [2], 4) = 0 +0 write(4,...,10000) = 10000 +0 write(4,...,10000) = 10000 // Set tcp-repair stuff, particularly TCP_RECV_QUEUE +0 setsockopt(4, SOL_TCP, 19, [1], 4) = 0 +0 setsockopt(4, SOL_TCP, 20, [1], 4) = 0 // This now will make the write push the remaining segments +0 setsockopt(4, SOL_SOCKET, 47, [20000], 4) = 0 +0 `sysctl -w net.ipv4.tcp_limit_output_bytes=130000` // Now we will crash +0 write(4,...,1000) = 1000 This happens since ec3423257508 (tcp: fix retransmission in repair mode). Prior to that, the call to tcp_push was prevented by a check for tp->repair. The patch fixes it, by adding the new goto-label out_nopush. When exiting tcp_sendmsg and a push is not required, which is the case for tp->repair, we go to this label. When repairing and calling send() with TCP_RECV_QUEUE, the data is actually put in the receive-queue. So, no push is required because no data has been added to the send-queue. Cc: Andrew Vagin Cc: Pavel Emelyanov Fixes: ec3423257508 (tcp: fix retransmission in repair mode) Signed-off-by: Christoph Paasch Acked-by: Andrew Vagin Acked-by: Pavel Emelyanov Signed-off-by: David S. Miller --- net/ipv4/tcp.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index eb1dde37e678..9d2118e5fbc7 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1108,7 +1108,7 @@ int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, if (unlikely(tp->repair)) { if (tp->repair_queue == TCP_RECV_QUEUE) { copied = tcp_send_rcvq(sk, msg, size); - goto out; + goto out_nopush; } err = -EINVAL; @@ -1282,6 +1282,7 @@ wait_for_memory: out: if (copied) tcp_push(sk, flags, mss_now, tp->nonagle, size_goal); +out_nopush: release_sock(sk); return copied + copied_syn; -- 2.30.2