syzbot


WARNING in em_nbyte_match

Status: upstream: reported C repro on 2025/12/06 11:58
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+aa4eb7c67913dbd88f56@syzkaller.appspotmail.com
First crash: 6d22h, last: 6d05h
Bug presence (2)
Date Name Commit Repro Result
2025/12/07 linux-6.6.y (ToT) 5fa4793a2d2d C [report] WARNING in em_nbyte_match
2025/12/07 upstream (ToT) 37bb2e7217b0 C Didn't crash
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING in em_nbyte_match net -1 C done 7 6d22h 21d 26/29 upstream: reported C repro on 2025/11/21 15:29
linux-6.1 WARNING in em_nbyte_match origin:lts-only -1 C 9 4d08h 6d22h 0/3 upstream: reported C repro on 2025/12/06 11:53

Sample crash report:
syzkaller0: entered promiscuous mode
syzkaller0: entered allmulticast mode
------------[ cut here ]------------
WARNING: CPU: 1 PID: 5949 at include/linux/skbuff.h:2871 skb_transport_header include/linux/skbuff.h:2871 [inline]
WARNING: CPU: 1 PID: 5949 at include/linux/skbuff.h:2871 tcf_get_base_ptr include/net/pkt_cls.h:528 [inline]
WARNING: CPU: 1 PID: 5949 at include/linux/skbuff.h:2871 em_nbyte_match+0x2d0/0x3e0 net/sched/em_nbyte.c:43
Modules linked in:
CPU: 1 PID: 5949 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:skb_transport_header include/linux/skbuff.h:2871 [inline]
RIP: 0010:tcf_get_base_ptr include/net/pkt_cls.h:528 [inline]
RIP: 0010:em_nbyte_match+0x2d0/0x3e0 net/sched/em_nbyte.c:43
Code: c0 eb 07 e8 02 e9 e2 f8 31 c0 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 ec e8 e2 f8 0f 0b e9 e5 fe ff ff e8 e0 e8 e2 f8 <0f> 0b e9 00 fe ff ff 89 d1 80 e1 07 fe c1 38 c1 0f 8c 7a fd ff ff
RSP: 0018:ffffc9000461f138 EFLAGS: 00010293
RAX: ffffffff88a2a7e0 RBX: ffff888025217dc0 RCX: ffff888029728000
RDX: 0000000000000000 RSI: 000000000000ffff RDI: 000000000000ffff
RBP: 000000000000ffff R08: ffff888029728000 R09: 0000000000000003
R10: 0000000000000002 R11: 0000000000000000 R12: dffffc0000000000
R13: 1ffff11004a42fce R14: ffff88802f748dc0 R15: 1ffff11005ee91b8
FS:  000055557dc13500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3164da1796 CR3: 00000000783fa000 CR4: 00000000003506e0
Call Trace:
 <TASK>
 tcf_em_match net/sched/ematch.c:494 [inline]
 __tcf_em_tree_match+0x1a8/0x760 net/sched/ematch.c:520
 tcf_em_tree_match include/net/pkt_cls.h:501 [inline]
 basic_classify+0x115/0x2d0 net/sched/cls_basic.c:50
 tc_classify include/net/tc_wrapper.h:227 [inline]
 __tcf_classify net/sched/cls_api.c:1704 [inline]
 tcf_classify+0x4c4/0xeb0 net/sched/cls_api.c:1788
 multiq_classify net/sched/sch_multiq.c:39 [inline]
 multiq_enqueue+0xfe/0x4b0 net/sched/sch_multiq.c:66
 dev_qdisc_enqueue+0x48/0x220 net/core/dev.c:3824
 __dev_xmit_skb net/core/dev.c:3913 [inline]
 __dev_queue_xmit+0xe10/0x35a0 net/core/dev.c:4391
 packet_snd net/packet/af_packet.c:3137 [inline]
 packet_sendmsg+0x3b47/0x4d30 net/packet/af_packet.c:3169
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 ____sys_sendmsg+0x5bf/0x950 net/socket.c:2595
 ___sys_sendmsg+0x220/0x290 net/socket.c:2649
 __sys_sendmsg net/socket.c:2678 [inline]
 __do_sys_sendmsg net/socket.c:2687 [inline]
 __se_sys_sendmsg+0x1a5/0x270 net/socket.c:2685
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f0d1bd8f749
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:00007ffcb80bb988 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f0d1bfe5fa0 RCX: 00007f0d1bd8f749
RDX: 0000000000000004 RSI: 00002000000000c0 RDI: 0000000000000007
RBP: 00007f0d1be13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0d1bfe5fa0 R14: 00007f0d1bfe5fa0 R15: 0000000000000003
 </TASK>

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/12/06 13:11 linux-6.6.y 4791134e4aeb d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in em_nbyte_match
2025/12/06 11:57 linux-6.6.y 4791134e4aeb d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in em_nbyte_match
2025/12/06 11:57 linux-6.6.y 4791134e4aeb d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in em_nbyte_match
* Struck through repros no longer work on HEAD.