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Mon, 12 Oct 2026 02:28:36 -0700 (PDT) Date: Mon, 12 Oct 2026 02:28:36 -0700 In-Reply-To: <20261012044322.503949-1-dungvn2345@gmail.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6acca844.8cdf6287.1eb53.0122.GAE@google.com> Subject: [syzbot ci] Re: net/sched: sch_netem: prevent packet length underflow with negative overhead From: syzbot ci To: davem@davemloft.net, dungvn2345@gmail.com, edumazet@kernel.org, hagen@jauu.net, horms@kernel.org, jhs@mojatatu.com, jiri@resnulli.us, kuba@kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, pabeni@redhat.com, stable@vger.kernel.org, stephen@networkplumber.org Cc: syzbot@lists.linux.dev, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" 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: 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 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 --- This report is generated by a bot. It may contain errors. syzbot ci engineers can be reached at syzkaller@googlegroups.com. To test a fix for this bug, please reply with `#syz test` (on a separate line) and attach the patch to the email. Notes: - The patch will be applied on top of the tested series (as an incremental fix). - To test a new version of the whole series, please send it directly to syzbot@lists.linux.dev. - Arguments like custom git repos and branches are not supported.