UBSAN: division-overflow in netem_enqueue

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    3db1a3fa Merge tag 'staging-5.11-rc1' of git://git.kernel...
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1213cf60d00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a6e6725884106332
dashboard link: https://syzkaller.appspot.com/bug?extid=c32f013ef7b11871dba6
compiler:       gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c32f013ef7b11871dba6@xxxxxxxxxxxxxxxxxxxxxxxxx

================================================================================
UBSAN: division-overflow in net/sched/sch_netem.c:516:27
division by zero
CPU: 0 PID: 12279 Comm: syz-executor.4 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 ubsan_epilogue+0xb/0x5a lib/ubsan.c:148
 __ubsan_handle_divrem_overflow.cold+0x7c/0xd0 lib/ubsan.c:252
 netem_enqueue.cold+0x17/0xbc net/sched/sch_netem.c:516
 netem_enqueue+0x2095/0x34e0 net/sched/sch_netem.c:483
 __dev_xmit_skb net/core/dev.c:3789 [inline]
 __dev_queue_xmit+0x19ec/0x2ef0 net/core/dev.c:4101
 __netlink_deliver_tap_skb net/netlink/af_netlink.c:295 [inline]
 __netlink_deliver_tap net/netlink/af_netlink.c:313 [inline]
 netlink_deliver_tap+0x9cb/0xc00 net/netlink/af_netlink.c:326
 netlink_deliver_tap_kernel net/netlink/af_netlink.c:335 [inline]
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0x5e5/0x7d0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x907/0xe10 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xd3/0x130 net/socket.c:672
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2336
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2390
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2423
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45e219
Code: 0d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 db b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f735a38fc68 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045e219
RDX: 0000000020000000 RSI: 0000000020000200 RDI: 0000000000000003
RBP: 000000000119bfc0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000119bf8c
R13: 00007ffecded56ef R14: 00007f735a3909c0 R15: 000000000119bf8c
================================================================================


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