net/ipv4: division by 0 in tcp_select_window

[Dmitry Vyukov]

Hello,

The following program triggers division by 0 in tcp_select_window:

https://gist.githubusercontent.com/dvyukov/ef28c0fd2ab57a655508ef7621b12e6c/raw/079011e2a9523a390b0621cbc1e5d9d5e637fd6d/gistfile1.txt

divide error: 0000 [#1] SMP KASAN
Modules linked in:
CPU: 3 PID: 0 Comm: swapper/3 Not tainted 4.10.0+ #270
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff88006c236340 task.stack: ffff88006c248000
RIP: 0010:__tcp_select_window+0x6db/0x920 net/ipv4/tcp_output.c:2585
RSP: 0018:ffff88006cf86b40 EFLAGS: 00010206
RAX: 00000000000000c4 RBX: ffff88006cf86cd8 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8800686228bd
RBP: ffff88006cf86d00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000004 R11: ffffed000d9f0e18 R12: 00000000000000c4
R13: 000000000000a700 R14: ffff880068622040 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88006cf80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020e5cff8 CR3: 0000000005021000 CR4: 00000000001406e0
Call Trace:
<IRQ>
tcp_select_window net/ipv4/tcp_output.c:270 [inline]
tcp_transmit_skb+0xc35/0x3460 net/ipv4/tcp_output.c:1014
tcp_xmit_probe_skb+0x36d/0x440 net/ipv4/tcp_output.c:3528
tcp_write_wakeup+0x23b/0x6d0 net/ipv4/tcp_output.c:3577
tcp_send_probe0+0xbf/0x5d0 net/ipv4/tcp_output.c:3593
tcp_probe_timer net/ipv4/tcp_timer.c:362 [inline]
tcp_write_timer_handler+0x849/0x9d0 net/ipv4/tcp_timer.c:578
tcp_write_timer+0x164/0x180 net/ipv4/tcp_timer.c:592
call_timer_fn+0x241/0x820 kernel/time/timer.c:1266
expire_timers kernel/time/timer.c:1305 [inline]
__run_timers+0x960/0xcf0 kernel/time/timer.c:1599
run_timer_softirq+0x21/0x80 kernel/time/timer.c:1612
__do_softirq+0x31f/0xbe7 kernel/softirq.c:284
invoke_softirq kernel/softirq.c:364 [inline]
irq_exit+0x1cc/0x200 kernel/softirq.c:405
exiting_irq arch/x86/include/asm/apic.h:658 [inline]
smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:962
apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:487
RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
RSP: 0018:ffff88006c24fc10 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff10
RAX: dffffc0000000000 RBX: 1ffff1000d849f85 RCX: 0000000000000000
RDX: 1ffffffff0a18ebc RSI: 0000000000000001 RDI: ffffffff850c75e0
RBP: ffff88006c24fc10 R08: ffff88007fff70dc R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 1ffff1000d849fa9
R13: ffff88006c24fcc8 R14: ffffffff856972b8 R15: ffff88006c24fe68
</IRQ>
arch_safe_halt arch/x86/include/asm/paravirt.h:98 [inline]
default_idle+0xbf/0x440 arch/x86/kernel/process.c:271
arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:262
default_idle_call+0x36/0x90 kernel/sched/idle.c:96
cpuidle_idle_call kernel/sched/idle.c:154 [inline]
do_idle+0x373/0x520 kernel/sched/idle.c:243
cpu_startup_entry+0x18/0x20 kernel/sched/idle.c:345
start_secondary+0x36c/0x460 arch/x86/kernel/smpboot.c:272
start_cpu+0x14/0x14 arch/x86/kernel/head_64.S:306
Code: 5d c3 e8 99 0d e5 fd 45 85 ff 44 89 bd 74 fe ff ff 0f 8f 14 fc
ff ff 45 31 e4 eb 93 e8 7f 0d e5 fd 8b b5 74 fe ff ff 44 89 e0 99 <f7>
fe 41 89 c4 44 0f af e6 e9 71 ff ff ff e8 62 0d e5 fd 4c 89
RIP: __tcp_select_window+0x6db/0x920 net/ipv4/tcp_output.c:2585 RSP:
ffff88006cf86b40
---[ end trace 5efcbe8231e36800 ]---

On commit c82be9d2244aacea9851c86f4fb74694c99cd874.

The guy that resets mss seems to be
inet_csk_listen_start->inet_csk_delack_init. After that the timer
fires and divides by icsk->icsk_ack.rcv_mss==0.

[Dmitry Vyukov]

Wonder if this has been causing other crashes like this one?

------------[ cut here ]------------
kernel BUG at net/ipv4/tcp_output.c:2748!
Call Trace:
<IRQ>
tcp_retransmit_skb+0x2e/0x230 net/ipv4/tcp_output.c:2822
tcp_retransmit_timer+0x104c/0x2d50 net/ipv4/tcp_timer.c:491
tcp_write_timer_handler+0x334/0x9d0 net/ipv4/tcp_timer.c:574

tcp_write_timer+0x164/0x180 net/ipv4/tcp_timer.c:592
call_timer_fn+0x241/0x820 kernel/time/timer.c:1266
expire_timers kernel/time/timer.c:1305 [inline]
__run_timers+0x960/0xcf0 kernel/time/timer.c:1599
run_timer_softirq+0x21/0x80 kernel/time/timer.c:1612
__do_softirq+0x31f/0xbe7 kernel/softirq.c:284
invoke_softirq kernel/softirq.c:364 [inline]
irq_exit+0x1cc/0x200 kernel/softirq.c:405
exiting_irq arch/x86/include/asm/apic.h:658 [inline]
smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:962
apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:487

if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
BUG();

[Eric Dumazet]

On Fri, Mar 3, 2017 at 10:10 AM, Dmitry Vyukov <dvy...@google.com> wrote:
> Hello,
>
> The following program triggers division by 0 in tcp_select_window:
>
> https://gist.githubusercontent.com/dvyukov/ef28c0fd2ab57a655508ef7621b12e6c/raw/079011e2a9523a390b0621cbc1e5d9d5e637fd6d/gistfile1.txt

Yeah, tcp_disconnect() should never have existed in the first place.

We'll send a patch, unless you take care of this before us .

Thanks.

[Eric Dumazet]

On Fri, Mar 3, 2017 at 10:24 AM, Dmitry Vyukov <dvy...@google.com> wrote:
> On Fri, Mar 3, 2017 at 7:10 PM, Dmitry Vyukov <dvy...@google.com> wrote:
>> Hello,
>>

> Wonder if this has been causing other crashes like this one?
>
> ------------[ cut here ]------------
> kernel BUG at net/ipv4/tcp_output.c:2748!
> Call Trace:
> <IRQ>
> tcp_retransmit_skb+0x2e/0x230 net/ipv4/tcp_output.c:2822
> tcp_retransmit_timer+0x104c/0x2d50 net/ipv4/tcp_timer.c:491
> tcp_write_timer_handler+0x334/0x9d0 net/ipv4/tcp_timer.c:574
> tcp_write_timer+0x164/0x180 net/ipv4/tcp_timer.c:592
> call_timer_fn+0x241/0x820 kernel/time/timer.c:1266
> expire_timers kernel/time/timer.c:1305 [inline]
> __run_timers+0x960/0xcf0 kernel/time/timer.c:1599
> run_timer_softirq+0x21/0x80 kernel/time/timer.c:1612
> __do_softirq+0x31f/0xbe7 kernel/softirq.c:284
> invoke_softirq kernel/softirq.c:364 [inline]
> irq_exit+0x1cc/0x200 kernel/softirq.c:405
> exiting_irq arch/x86/include/asm/apic.h:658 [inline]
> smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:962
> apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:487
>
> if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
> if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
> BUG();

This path uses a socket lock. Probably different problem.

[Eric Dumazet]

Could you try this first patch ?

Probably others will also be needed.

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 40d893556e6701ace6a02903e53c45822d6fa56d..2187ebf1f270d19e6dd019b8f9df5eef8d018e03 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -552,7 +552,8 @@ void tcp_write_timer_handler(struct sock *sk)
struct inet_connection_sock *icsk = inet_csk(sk);
int event;

- if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
+ if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
+ !icsk->icsk_pending)
goto out;

if (time_after(icsk->icsk_timeout, jiffies)) {