[Android 5.15] divide error in netem_enqueue

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a825653ab7af Revert "skmsg: convert struct sk_msg_sg::copy..
git tree: android13-5.15-lts
console+strace: https://syzkaller.appspot.com/x/log.txt?x=13659679580000
kernel config: https://syzkaller.appspot.com/x/.config?x=43676e801f1929a9
dashboard link: https://syzkaller.appspot.com/bug?extid=3ea4b9e11653a934dace
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=117a7679580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17659679580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/45afce6d1a05/disk-a825653a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c0af5ca8d028/vmlinux-a825653a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3d3d0039c7cc/bzImage-a825653a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3ea4b9...@syzkaller.appspotmail.com

divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 309 Comm: syz-executor121 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:netem_enqueue+0x17f8/0x3750 net/sched/sch_netem.c:511
Code: 00 4c 89 e9 45 8b 6d 70 48 89 4c 24 28 4c 8d 61 74 4c 89 e1 48 c1 e9 03 0f b6 0c 31 84 c9 0f 85 34 19 00 00 45 2b 2c 24 31 d2 <41> f7 f5 48 01 d3 48 89 d8 48 c1 e8 03 0f b6 04 30 84 c0 0f 85 45
RSP: 0018:ffffc90000a573e0 EFLAGS: 00010246
RAX: 00000000fc1fc2f4 RBX: ffff88810f5ae880 RCX: 0000000000000000
RDX: 0000000000000000 RSI: dffffc0000000000 RDI: ffff88810d7c7570
RBP: ffffc90000a57510 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff5200014ade4 R12: ffff88810d7c7574
R13: 0000000000000000 R14: 0000000000000080 R15: 0000000000000000
FS: 00005555752c53c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000010c95c000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
netem_enqueue+0x1928/0x3750 net/sched/sch_netem.c:534
dev_qdisc_enqueue net/core/dev.c:3873 [inline]
__dev_xmit_skb net/core/dev.c:3957 [inline]
__dev_queue_xmit+0xc35/0x2d60 net/core/dev.c:4274
dev_queue_xmit+0x17/0x20 net/core/dev.c:4355
tpacket_snd net/packet/af_packet.c:2897 [inline]
packet_sendmsg+0x224d/0x5060 net/packet/af_packet.c:3123
sock_sendmsg_nosec net/socket.c:704 [inline]
__sock_sendmsg net/socket.c:716 [inline]
sock_write_iter+0x2a6/0x3a0 net/socket.c:1080
call_write_iter include/linux/fs.h:2212 [inline]
new_sync_write fs/read_write.c:507 [inline]
vfs_write+0x831/0xfd0 fs/read_write.c:594
ksys_write+0x14a/0x260 fs/read_write.c:647
__do_sys_write fs/read_write.c:659 [inline]
__se_sys_write fs/read_write.c:656 [inline]
__x64_sys_write+0x7b/0x90 fs/read_write.c:656
x64_sys_call+0x8ef/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f0dbd304a89
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 00 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdaa013098 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f0dbd304a89
RDX: 0000000000000001 RSI: 0000200000000000 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000005 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 00007ffdaa0130e0
</TASK>
Modules linked in:
---[ end trace 5558f3f345470bd9 ]---
RIP: 0010:netem_enqueue+0x17f8/0x3750 net/sched/sch_netem.c:511
Code: 00 4c 89 e9 45 8b 6d 70 48 89 4c 24 28 4c 8d 61 74 4c 89 e1 48 c1 e9 03 0f b6 0c 31 84 c9 0f 85 34 19 00 00 45 2b 2c 24 31 d2 <41> f7 f5 48 01 d3 48 89 d8 48 c1 e8 03 0f b6 04 30 84 c0 0f 85 45
RSP: 0018:ffffc90000a573e0 EFLAGS: 00010246
RAX: 00000000fc1fc2f4 RBX: ffff88810f5ae880 RCX: 0000000000000000
RDX: 0000000000000000 RSI: dffffc0000000000 RDI: ffff88810d7c7570
RBP: ffffc90000a57510 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff5200014ade4 R12: ffff88810d7c7574
R13: 0000000000000000 R14: 0000000000000080 R15: 0000000000000000
FS: 00005555752c53c0(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000010c95c000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 00 4c 89 e9 add %cl,-0x17(%rcx,%rcx,4)
4: 45 8b 6d 70 mov 0x70(%r13),%r13d
8: 48 89 4c 24 28 mov %rcx,0x28(%rsp)
d: 4c 8d 61 74 lea 0x74(%rcx),%r12
11: 4c 89 e1 mov %r12,%rcx
14: 48 c1 e9 03 shr $0x3,%rcx
18: 0f b6 0c 31 movzbl (%rcx,%rsi,1),%ecx
1c: 84 c9 test %cl,%cl
1e: 0f 85 34 19 00 00 jne 0x1958
24: 45 2b 2c 24 sub (%r12),%r13d
28: 31 d2 xor %edx,%edx
* 2a: 41 f7 f5 div %r13d <-- trapping instruction
2d: 48 01 d3 add %rdx,%rbx
30: 48 89 d8 mov %rbx,%rax
33: 48 c1 e8 03 shr $0x3,%rax
37: 0f b6 04 30 movzbl (%rax,%rsi,1),%eax
3b: 84 c0 test %al,%al
3d: 0f .byte 0xf
3e: 85 .byte 0x85
3f: 45 rex.RB


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup