[syzbot ci] Re: net/sched: sch_netem: prevent packet length underflow with negative overhead

[syzbot ci] Re: net/sched: sch_netem: prevent packet length underflow with negative overhead

[syzbot ci]

syzbot ci has tested the following series

[v2] net/sched: sch_netem: prevent packet length underflow with negative overhead
https://lore.kernel.org/all/20261012044322.503949-1-dungvn2345@gmail.com
* [PATCH net v2] net/sched: sch_netem: prevent packet length underflow with negative overhead

and found the following issue:
divide error in netem_enqueue

Full report is available here:
https://ci.syzbot.org/series/eff5cc04-13f7-4a28-9b83-b6e0de530bc2

***

divide error in netem_enqueue

tree:      net
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net.git
base:      af32da41b0327b9c6a37856ba82b6760d6c8d10e
arch:      amd64
compiler:  Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
config:    https://ci.syzbot.org/builds/bf12d8a1-2cda-46fc-9150-cadd809b1c71/config

Oops: divide error: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 17390 Comm: syz.0.2912 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:netem_enqueue+0x20f6/0x3300
Code: 8b 74 24 38 48 8b 44 24 50 42 80 3c 28 00 74 08 4c 89 f7 e8 cc f4 51 f8 49 8b 0e 4c 89 f8 48 f7 25 b7 9c 8b 04 48 89 4c 24 78 <48> f7 74 24 78 48 b9 ff ff ff ff ff ff ff 7f 48 39 c8 48 0f 42 c8
RSP: 0018:ffffc900082cf4b0 EFLAGS: 00010a07
RAX: 3599740d73380000 RBX: 0000005c44b22572 RCX: 000000000000002c
RDX: 0000000000000077 RSI: 00000000000001ed RDI: 00000000000001ee
RBP: ffff88810e973000 R08: ffffffff917a717f R09: 1ffffffff22f4e2f
R10: dffffc0000000000 R11: ffffffff81776d40 R12: ffff888026e62330
R13: dffffc0000000000 R14: ffff88810e9732b0 R15: 0000020000176c00
FS:  00007f87167196c0(0000) GS:ffff88818c4bf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8716718ff8 CR3: 000000002756e000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 netem_enqueue+0x16f1/0x3300
 dev_qdisc_enqueue+0x4e/0x260
 __dev_queue_xmit+0x1b6c/0x3920
 packet_sendmsg+0x3f11/0x51a0
 sock_sendmsg_nosec+0x13a/0x180
 __sys_sendto+0x408/0x5a0
 __x64_sys_sendto+0xde/0x100
 do_syscall_64+0x166/0x520
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f871579e1d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f8716719028 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007f8715a25fa0 RCX: 00007f871579e1d9
RDX: 00000000000005dc RSI: 0000200000000280 RDI: 0000000000000009
RBP: 00007f8715835888 R08: 0000200000000140 R09: 0000000000000014
R10: 0000000000004009 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8715a26038 R14: 00007f8715a25fa0 R15: 00007ffc85273198
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:netem_enqueue+0x20f6/0x3300
Code: 8b 74 24 38 48 8b 44 24 50 42 80 3c 28 00 74 08 4c 89 f7 e8 cc f4 51 f8 49 8b 0e 4c 89 f8 48 f7 25 b7 9c 8b 04 48 89 4c 24 78 <48> f7 74 24 78 48 b9 ff ff ff ff ff ff ff 7f 48 39 c8 48 0f 42 c8
RSP: 0018:ffffc900082cf4b0 EFLAGS: 00010a07
RAX: 3599740d73380000 RBX: 0000005c44b22572 RCX: 000000000000002c
RDX: 0000000000000077 RSI: 00000000000001ed RDI: 00000000000001ee
RBP: ffff88810e973000 R08: ffffffff917a717f R09: 1ffffffff22f4e2f
R10: dffffc0000000000 R11: ffffffff81776d40 R12: ffff888026e62330
R13: dffffc0000000000 R14: ffff88810e9732b0 R15: 0000020000176c00
FS:  00007f87167196c0(0000) GS:ffff88818c4bf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8716718ff8 CR3: 000000002756e000 CR4: 00000000000006f0


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
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Notes:
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