[syzbot] [net?] WARNING in em_nbyte_match

[syzbot <syzbot+f3a497f02c389d86ef16@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    8e621c9a3375 Merge tag 'net-6.18-rc7' of git://git.kernel...
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=135a0e92580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=14b6a9313e132a6b
dashboard link: https://syzkaller.appspot.com/bug?extid=f3a497f02c389d86ef16
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15e83658580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=149b4484580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bd46b2cfa172/disk-8e621c9a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/55fd403d139a/vmlinux-8e621c9a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f79c45db6fe5/bzImage-8e621c9a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f3a497f02c389d86ef16@syzkaller.appspotmail.com

syzkaller0: entered promiscuous mode
syzkaller0: entered allmulticast mode
------------[ cut here ]------------
WARNING: CPU: 0 PID: 6013 at ./include/linux/skbuff.h:3071 skb_transport_header include/linux/skbuff.h:3071 [inline]
WARNING: CPU: 0 PID: 6013 at ./include/linux/skbuff.h:3071 tcf_get_base_ptr include/net/pkt_cls.h:539 [inline]
WARNING: CPU: 0 PID: 6013 at ./include/linux/skbuff.h:3071 em_nbyte_match+0x2d8/0x3f0 net/sched/em_nbyte.c:43
Modules linked in:
CPU: 0 UID: 0 PID: 6013 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:skb_transport_header include/linux/skbuff.h:3071 [inline]
RIP: 0010:tcf_get_base_ptr include/net/pkt_cls.h:539 [inline]
RIP: 0010:em_nbyte_match+0x2d8/0x3f0 net/sched/em_nbyte.c:43
Code: 31 c0 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d e9 8d 08 e4 01 cc e8 a7 a7 5a f8 90 0f 0b 90 e9 de fe ff ff e8 99 a7 5a f8 90 <0f> 0b 90 e9 f7 fd ff ff 89 d1 80 e1 07 fe c1 38 c1 0f 8c 71 fd ff
RSP: 0018:ffffc900038fefd8 EFLAGS: 00010293
RAX: ffffffff89655c27 RBX: ffff88803039f3c0 RCX: ffff88802f1d0000
RDX: 0000000000000000 RSI: 000000000000ffff RDI: 000000000000ffff
RBP: 000000000000ffff R08: ffff88802f1d0000 R09: 0000000000000003
R10: 0000000000000002 R11: 0000000000000000 R12: dffffc0000000000
R13: 1ffff11006073e8e R14: ffff8880301e5580 R15: 1ffff1100603cab0
FS:  00005555576be500(0000) GS:ffff88812613b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000002280 CR3: 0000000062390000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 tcf_em_match net/sched/ematch.c:494 [inline]
 __tcf_em_tree_match+0x1ac/0x770 net/sched/ematch.c:520
 tcf_em_tree_match include/net/pkt_cls.h:512 [inline]
 basic_classify+0x115/0x2d0 net/sched/cls_basic.c:50
 tc_classify include/net/tc_wrapper.h:197 [inline]
 __tcf_classify net/sched/cls_api.c:1764 [inline]
 tcf_classify+0x4cf/0x1140 net/sched/cls_api.c:1860
 multiq_classify net/sched/sch_multiq.c:39 [inline]
 multiq_enqueue+0xfd/0x4c0 net/sched/sch_multiq.c:66
 dev_qdisc_enqueue+0x4e/0x260 net/core/dev.c:4118
 __dev_xmit_skb net/core/dev.c:4214 [inline]
 __dev_queue_xmit+0xe83/0x3b50 net/core/dev.c:4729
 packet_snd net/packet/af_packet.c:3076 [inline]
 packet_sendmsg+0x3e33/0x5080 net/packet/af_packet.c:3108
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 ____sys_sendmsg+0x505/0x830 net/socket.c:2630
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684
 __sys_sendmsg net/socket.c:2716 [inline]
 __do_sys_sendmsg net/socket.c:2721 [inline]
 __se_sys_sendmsg net/socket.c:2719 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2719
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f02b7d8f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffef050ec08 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f02b7fe5fa0 RCX: 00007f02b7d8f749
RDX: 0000000000000004 RSI: 00002000000000c0 RDI: 0000000000000007
RBP: 00007f02b7e13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f02b7fe5fa0 R14: 00007f02b7fe5fa0 R15: 0000000000000003
 </TASK>


---
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 syzkaller@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