divide error in tcp_reno_cong_avoid

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: eb575cd5 Linux 4.19.195
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=11e04bd0300000
kernel config: https://syzkaller.appspot.com/x/.config?x=5506475cccaff975
dashboard link: https://syzkaller.appspot.com/bug?extid=666cdff0b2066dc63af9
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13e69e34300000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14527e34300000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+666cdf...@syzkaller.appspotmail.com

divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 10623 Comm: syz-executor153 Not tainted 4.19.195-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:tcp_cong_avoid_ai net/ipv4/tcp_cong.c:426 [inline]
RIP: 0010:tcp_reno_cong_avoid+0x28c/0x310 net/ipv4/tcp_cong.c:456
Code: ab 98 08 00 00 e8 d4 38 83 fa 45 85 e4 0f 85 aa fe ff ff 5b 5d 41 5c 41 5d 41 5e e9 4e 37 83 fa e8 49 37 83 fa 44 89 e0 31 d2 <f7> f5 41 01 c5 89 93 9c 08 00 00 44 89 ab 98 08 00 00 e9 fb fe ff
RSP: 0018:ffff8880ba1075b0 EFLAGS: 00010246
RAX: 0000000000000001 RBX: ffff8880af70a300 RCX: ffffffff86df46e9
RDX: 0000000000000000 RSI: ffffffff86df47e7 RDI: 0000000000000004
RBP: 0000000000000000 R08: ffff8880ba1077e8 R09: 0000000000000000
R10: 0000000000000004 R11: ffffffff8c66205b R12: 0000000000000001
R13: 0000000000000001 R14: 00000000ffffffff R15: 0000000000000000
FS: 00007ff3129e8700(0000) GS:ffff8880ba100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020200000 CR3: 000000009d4c0000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
tcp_cdg_cong_avoid+0x16f/0x15b0 net/ipv4/tcp_cdg.c:292
tcp_cong_avoid net/ipv4/tcp_input.c:2972 [inline]
tcp_cong_control net/ipv4/tcp_input.c:3325 [inline]
tcp_ack+0x2f0f/0x51d0 net/ipv4/tcp_input.c:3715
tcp_rcv_established+0x66b/0x1ea0 net/ipv4/tcp_input.c:5666
tcp_v4_do_rcv+0x5d6/0x870 net/ipv4/tcp_ipv4.c:1547
tcp_v4_rcv+0x2c03/0x3b80 net/ipv4/tcp_ipv4.c:1832
ip_local_deliver_finish+0x495/0xc00 net/ipv4/ip_input.c:215
NF_HOOK include/linux/netfilter.h:289 [inline]
ip_local_deliver+0x188/0x500 net/ipv4/ip_input.c:256
dst_input include/net/dst.h:461 [inline]
ip_rcv_finish+0x1ca/0x2e0 net/ipv4/ip_input.c:414
NF_HOOK include/linux/netfilter.h:289 [inline]
ip_rcv+0xca/0x3c0 net/ipv4/ip_input.c:524
__netif_receive_skb_one_core+0x114/0x180 net/core/dev.c:4954
__netif_receive_skb+0x27/0x1c0 net/core/dev.c:5066
process_backlog+0x241/0x700 net/core/dev.c:5848
napi_poll net/core/dev.c:6272 [inline]
net_rx_action+0x4ac/0xfb0 net/core/dev.c:6338
__do_softirq+0x265/0x980 kernel/softirq.c:292
do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1092
</IRQ>
do_softirq.part.0+0x160/0x1c0 kernel/softirq.c:336
do_softirq kernel/softirq.c:328 [inline]
__local_bh_enable_ip+0x20e/0x270 kernel/softirq.c:189
tcp_sendmsg+0x36/0x40 net/ipv4/tcp.c:1463
inet_sendmsg+0x132/0x5a0 net/ipv4/af_inet.c:798
sock_sendmsg_nosec net/socket.c:622 [inline]
sock_sendmsg+0xc3/0x120 net/socket.c:632
__sys_sendto+0x21a/0x320 net/socket.c:1787
__do_sys_sendto net/socket.c:1799 [inline]
__se_sys_sendto net/socket.c:1795 [inline]
__x64_sys_sendto+0xdd/0x1b0 net/socket.c:1795
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x451079
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 18 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff3129e8308 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000004cf4c8 RCX: 0000000000451079
RDX: 00000000fffffd46 RSI: 0000000020000240 RDI: 0000000000000004
RBP: 00000000004cf4c0 R08: 0000000000000000 R09: 00000000000001f4
R10: 00000000000081f4 R11: 0000000000000246 R12: 000000000049e6f4
R13: 00007ffc68fb8e9f R14: 00007ff3129e8400 R15: 0000000000022000
Modules linked in:
---[ end trace 4c7dc466bafcca32 ]---
RIP: 0010:tcp_cong_avoid_ai net/ipv4/tcp_cong.c:426 [inline]
RIP: 0010:tcp_reno_cong_avoid+0x28c/0x310 net/ipv4/tcp_cong.c:456
Code: ab 98 08 00 00 e8 d4 38 83 fa 45 85 e4 0f 85 aa fe ff ff 5b 5d 41 5c 41 5d 41 5e e9 4e 37 83 fa e8 49 37 83 fa 44 89 e0 31 d2 <f7> f5 41 01 c5 89 93 9c 08 00 00 44 89 ab 98 08 00 00 e9 fb fe ff
RSP: 0018:ffff8880ba1075b0 EFLAGS: 00010246
RAX: 0000000000000001 RBX: ffff8880af70a300 RCX: ffffffff86df46e9
RDX: 0000000000000000 RSI: ffffffff86df47e7 RDI: 0000000000000004
RBP: 0000000000000000 R08: ffff8880ba1077e8 R09: 0000000000000000
R10: 0000000000000004 R11: ffffffff8c66205b R12: 0000000000000001
R13: 0000000000000001 R14: 00000000ffffffff R15: 0000000000000000
FS: 00007ff3129e8700(0000) GS:ffff8880ba100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020200000 CR3: 000000009d4c0000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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