divide error in tcp_reno_cong_avoid

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 964f3712e6a7 Linux 4.14.240
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14ab2066300000
kernel config: https://syzkaller.appspot.com/x/.config?x=bcbf21141268a124
dashboard link: https://syzkaller.appspot.com/bug?extid=c2b8f403eb17260e6029
compiler: gcc version 10.2.1 20210110 (Debian 10.2.1-6)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=151b1d82300000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1539701a300000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c2b8f4...@syzkaller.appspotmail.com

divide error: 0000 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 1 PID: 8262 Comm: syz-executor101 Not tainted 4.14.240-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff888093fd2280 task.stack: ffff8880ae738000
RIP: 0010:tcp_cong_avoid_ai net/ipv4/tcp_cong.c:426 [inline]
RIP: 0010:tcp_reno_cong_avoid+0x24a/0x2d0 net/ipv4/tcp_cong.c:456
RSP: 0018:ffff8880ae73f718 EFLAGS: 00010246
RAX: 000000000000000d RBX: ffff8880b044f500 RCX: 0000000000000005
RDX: 0000000000000000 RSI: 000000002433d3dc RDI: ffff8880b044fd50
RBP: 0000000000000000 R08: ffff88823fff7058 R09: 0000000000000000
R10: ffff88823fff7057 R11: 00000008c0b25f66 R12: 000000000000000d
R13: 0000000000000001 R14: 00000000ffffffff R15: 0000000000000000
FS: 0000000001cc0300(0000) GS:ffff8880ba500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004b9110 CR3: 000000009a494000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
tcp_cdg_cong_avoid+0x13b/0x13f0 net/ipv4/tcp_cdg.c:292
tcp_cong_avoid net/ipv4/tcp_input.c:3011 [inline]
tcp_cong_control net/ipv4/tcp_input.c:3352 [inline]
tcp_ack+0x288d/0x4580 net/ipv4/tcp_input.c:3708
tcp_rcv_established+0x4fe/0x1810 net/ipv4/tcp_input.c:5572
tcp_v4_do_rcv+0x541/0x7d0 net/ipv4/tcp_ipv4.c:1476
sk_backlog_rcv include/net/sock.h:921 [inline]
__release_sock+0x12a/0x350 net/core/sock.c:2269
__sk_flush_backlog+0x22/0x30 net/core/sock.c:2289
sk_flush_backlog include/net/sock.h:1008 [inline]
tcp_sendmsg_locked+0x2486/0x2ef0 net/ipv4/tcp.c:1296
tcp_sendmsg+0x2b/0x40 net/ipv4/tcp.c:1457
inet_sendmsg+0x11a/0x4e0 net/ipv4/af_inet.c:762
sock_sendmsg_nosec net/socket.c:646 [inline]
sock_sendmsg+0xb5/0x100 net/socket.c:656
SYSC_sendto net/socket.c:1763 [inline]
SyS_sendto+0x1c7/0x2c0 net/socket.c:1731
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x44ba49
RSP: 002b:00007ffdf1453058 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000044ba49
RDX: 00000000fffffd46 RSI: 0000000020000240 RDI: 0000000000000004
RBP: 0000000000000000 R08: 0000000000000000 R09: 00000000000001f4
R10: 00000000000081f4 R11: 0000000000000246 R12: 00007ffdf1453080
R13: 00007ffdf1453090 R14: 0000000000007484 R15: 00007ffdf1453070
Code: f5 41 0f 47 ee 45 85 e4 89 ab 4c 08 00 00 0f 85 d5 fe ff ff 5b 5d 41 5c 41 5d 41 5e e9 70 02 3e fb e8 6b 02 3e fb 44 89 e0 31 d2 <f7> f5 41 01 c5 89 93 50 08 00 00 44 89 ab 4c 08 00 00 e9 09 ff
RIP: tcp_cong_avoid_ai net/ipv4/tcp_cong.c:426 [inline] RSP: ffff8880ae73f718
RIP: tcp_reno_cong_avoid+0x24a/0x2d0 net/ipv4/tcp_cong.c:456 RSP: ffff8880ae73f718
---[ end trace 09444daec56eee3d ]---


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