[syzbot] [net?] KMSAN: uninit-value in __fl_lookup (3)

[syzbot <syzbot+fa2f5b1fb06147be5e16@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    6a97c4d5262d Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=131bdb06580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=91978e795dcd971b
dashboard link: https://syzkaller.appspot.com/bug?extid=fa2f5b1fb06147be5e16
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e37d654ca33b/disk-6a97c4d5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dac2f748909e/vmlinux-6a97c4d5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/800a8a09004d/bzImage-6a97c4d5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fa2f5b1fb06147be5e16@syzkaller.appspotmail.com

syzkaller0: entered promiscuous mode
syzkaller0: entered allmulticast mode
=====================================================
BUG: KMSAN: uninit-value in __rht_ptr_rcu include/linux/rhashtable.h:388 [inline]
BUG: KMSAN: uninit-value in __rhashtable_lookup include/linux/rhashtable.h:631 [inline]
BUG: KMSAN: uninit-value in rhashtable_lookup include/linux/rhashtable.h:671 [inline]
BUG: KMSAN: uninit-value in rhashtable_lookup_fast include/linux/rhashtable.h:709 [inline]
BUG: KMSAN: uninit-value in __fl_lookup+0x6ce/0x940 net/sched/cls_flower.c:269
 __rht_ptr_rcu include/linux/rhashtable.h:388 [inline]
 __rhashtable_lookup include/linux/rhashtable.h:631 [inline]
 rhashtable_lookup include/linux/rhashtable.h:671 [inline]
 rhashtable_lookup_fast include/linux/rhashtable.h:709 [inline]
 __fl_lookup+0x6ce/0x940 net/sched/cls_flower.c:269
 fl_mask_lookup+0x305/0xd60 net/sched/cls_flower.c:302
 fl_classify+0x36b/0x780 net/sched/cls_flower.c:349
 tc_classify include/net/tc_wrapper.h:198 [inline]
 __tcf_classify net/sched/cls_api.c:1764 [inline]
 tcf_classify+0x855/0x1ca0 net/sched/cls_api.c:1860
 multiq_classify net/sched/sch_multiq.c:39 [inline]
 multiq_enqueue+0x82/0x5a0 net/sched/sch_multiq.c:66
 dev_qdisc_enqueue net/core/dev.c:4174 [inline]
 __dev_xmit_skb net/core/dev.c:4289 [inline]
 __dev_queue_xmit+0x23c3/0x5a00 net/core/dev.c:4831
 dev_queue_xmit include/linux/netdevice.h:3418 [inline]
 packet_xmit+0x8f/0x710 net/packet/af_packet.c:276
 packet_snd net/packet/af_packet.c:3082 [inline]
 packet_sendmsg+0x8c6b/0x9d60 net/packet/af_packet.c:3114
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0xf37/0xfd0 net/socket.c:2698
 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2752
 __sys_sendmsg net/socket.c:2784 [inline]
 __do_sys_sendmsg net/socket.c:2789 [inline]
 __se_sys_sendmsg net/socket.c:2787 [inline]
 __x64_sys_sendmsg+0x211/0x3e0 net/socket.c:2787
 x64_sys_call+0x1e20/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x134/0x390 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
 fl_set_masked_key net/sched/cls_flower.c:194 [inline]
 fl_mask_lookup+0x254/0xd60 net/sched/cls_flower.c:298
 fl_classify+0x36b/0x780 net/sched/cls_flower.c:349
 tc_classify include/net/tc_wrapper.h:198 [inline]
 __tcf_classify net/sched/cls_api.c:1764 [inline]
 tcf_classify+0x855/0x1ca0 net/sched/cls_api.c:1860
 multiq_classify net/sched/sch_multiq.c:39 [inline]
 multiq_enqueue+0x82/0x5a0 net/sched/sch_multiq.c:66
 dev_qdisc_enqueue net/core/dev.c:4174 [inline]
 __dev_xmit_skb net/core/dev.c:4289 [inline]
 __dev_queue_xmit+0x23c3/0x5a00 net/core/dev.c:4831
 dev_queue_xmit include/linux/netdevice.h:3418 [inline]
 packet_xmit+0x8f/0x710 net/packet/af_packet.c:276
 packet_snd net/packet/af_packet.c:3082 [inline]
 packet_sendmsg+0x8c6b/0x9d60 net/packet/af_packet.c:3114
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0xf37/0xfd0 net/socket.c:2698
 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2752
 __sys_sendmsg net/socket.c:2784 [inline]
 __do_sys_sendmsg net/socket.c:2789 [inline]
 __se_sys_sendmsg net/socket.c:2787 [inline]
 __x64_sys_sendmsg+0x211/0x3e0 net/socket.c:2787
 x64_sys_call+0x1e20/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x134/0x390 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
 __skb_flow_dissect+0xfdb/0xa060 net/core/flow_dissector.c:1182
 skb_flow_dissect include/linux/skbuff.h:1603 [inline]
 fl_classify+0x349/0x780 net/sched/cls_flower.c:346
 tc_classify include/net/tc_wrapper.h:198 [inline]
 __tcf_classify net/sched/cls_api.c:1764 [inline]
 tcf_classify+0x855/0x1ca0 net/sched/cls_api.c:1860
 multiq_classify net/sched/sch_multiq.c:39 [inline]
 multiq_enqueue+0x82/0x5a0 net/sched/sch_multiq.c:66
 dev_qdisc_enqueue net/core/dev.c:4174 [inline]
 __dev_xmit_skb net/core/dev.c:4289 [inline]
 __dev_queue_xmit+0x23c3/0x5a00 net/core/dev.c:4831
 dev_queue_xmit include/linux/netdevice.h:3418 [inline]
 packet_xmit+0x8f/0x710 net/packet/af_packet.c:276
 packet_snd net/packet/af_packet.c:3082 [inline]
 packet_sendmsg+0x8c6b/0x9d60 net/packet/af_packet.c:3114
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0xf37/0xfd0 net/socket.c:2698
 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2752
 __sys_sendmsg net/socket.c:2784 [inline]
 __do_sys_sendmsg net/socket.c:2789 [inline]
 __se_sys_sendmsg net/socket.c:2787 [inline]
 __x64_sys_sendmsg+0x211/0x3e0 net/socket.c:2787
 x64_sys_call+0x1e20/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x134/0x390 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4577 [inline]
 slab_alloc_node mm/slub.c:4899 [inline]
 kmem_cache_alloc_node_noprof+0x3cd/0x12c0 mm/slub.c:4951
 kmalloc_reserve net/core/skbuff.c:613 [inline]
 __alloc_skb+0x855/0x1190 net/core/skbuff.c:713
 alloc_skb include/linux/skbuff.h:1383 [inline]
 alloc_skb_with_frags+0xc5/0x990 net/core/skbuff.c:6743
 sock_alloc_send_pskb+0xacb/0xc60 net/core/sock.c:2998
 packet_alloc_skb net/packet/af_packet.c:2932 [inline]
 packet_snd net/packet/af_packet.c:3025 [inline]
 packet_sendmsg+0x6ed5/0x9d60 net/packet/af_packet.c:3114
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0xf37/0xfd0 net/socket.c:2698
 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2752
 __sys_sendmsg net/socket.c:2784 [inline]
 __do_sys_sendmsg net/socket.c:2789 [inline]
 __se_sys_sendmsg net/socket.c:2787 [inline]
 __x64_sys_sendmsg+0x211/0x3e0 net/socket.c:2787
 x64_sys_call+0x1e20/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x134/0x390 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 13869 Comm: syz.9.1335 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
=====================================================


---
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 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