syzbot
KASAN: use-after-free Read in llc_conn_ac_send_sabme_cmd_p_set_x
Status:
upstream: reported on 2026/07/25 04:49
Reported-by: syzbot+11738dbec49b83acb18b@syzkaller.appspotmail.com
First crash: 12d, last: 25m
Sample crash report:
==================================================================
BUG: KASAN: use-after-free in llc_conn_ac_send_sabme_cmd_p_set_x+0x332/0x3c0 net/llc/llc_c_ac.c:788
Read of size 1 at addr ffff88801d993010 by task kworker/1:1H/150
CPU: 1 PID: 150 Comm: kworker/1:1H Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: events_highpri snd_vmidi_output_work
Call Trace:
<IRQ>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
print_address_description+0x60/0x2d0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:434 [inline]
kasan_report+0xdf/0x130 mm/kasan/report.c:451
llc_conn_ac_send_sabme_cmd_p_set_x+0x332/0x3c0 net/llc/llc_c_ac.c:788
llc_exec_conn_trans_actions net/llc/llc_conn.c:442 [inline]
llc_conn_service net/llc/llc_conn.c:367 [inline]
llc_conn_state_process+0x506/0x12b0 net/llc/llc_conn.c:71
llc_process_tmr_ev net/llc/llc_c_ac.c:1445 [inline]
llc_conn_tmr_common_cb+0x336/0x7e0 net/llc/llc_c_ac.c:1331
call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
expire_timers kernel/time/timer.c:1699 [inline]
__run_timers+0x56c/0x810 kernel/time/timer.c:1970
run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
handle_softirqs+0x336/0x830 kernel/softirq.c:576
__do_softirq kernel/softirq.c:610 [inline]
invoke_softirq kernel/softirq.c:450 [inline]
__irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:finish_lock_switch+0x12f/0x290 kernel/sched/core.c:4804
Code: 83 c7 18 be ff ff ff ff e8 6e cb 6b 08 85 c0 74 46 4d 85 ff 75 62 e9 06 01 00 00 48 89 df e8 98 3a 75 08 e8 43 d7 2a 00 fb 5b <41> 5c 41 5d 41 5e 41 5f 5d c3 48 89 df e8 2f 0e fe ff 43 80 3c 2c
RSP: 0018:ffffc9000169f6d8 EFLAGS: 00000286
RAX: ee8ddabbbf835900 RBX: ffff88802c2fd940 RCX: ee8ddabbbf835900
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a4200
RBP: 1ffff11017227613 R08: ffffffff901ee1ef R09: 1ffffffff203dc3d
R10: dffffc0000000000 R11: fffffbfff203dc3e R12: ffff8880b913b088
R13: dffffc0000000000 R14: ffff8880b913ae08 R15: 0000000000000000
finish_task_switch+0x12f/0x650 kernel/sched/core.c:4921
context_switch kernel/sched/core.c:5052 [inline]
__schedule+0x11cb/0x4350 kernel/sched/core.c:6395
preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6571
preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6596
preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
_raw_spin_unlock_irqrestore+0x10d/0x120 kernel/locking/spinlock.c:194
spin_unlock_irqrestore include/linux/spinlock.h:419 [inline]
snd_rawmidi_transmit+0x349/0x400 sound/core/rawmidi.c:1417
snd_vmidi_output_work+0x1a2/0x3e0 sound/core/seq/seq_virmidi.c:151
process_one_work+0x867/0xff0 kernel/workqueue.c:2310
worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
kthread+0x42e/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>
Allocated by task 7169:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc mm/kasan/common.c:513 [inline]
__kasan_kmalloc+0xaf/0xe0 mm/kasan/common.c:522
kmalloc include/linux/slab.h:607 [inline]
kzalloc include/linux/slab.h:738 [inline]
llc_sap_alloc net/llc/llc_core.c:35 [inline]
llc_sap_open+0xda/0x330 net/llc/llc_core.c:102
llc_ui_autobind+0x1fa/0x4b0 net/llc/af_llc.c:306
llc_ui_connect+0x1c5/0xc70 net/llc/af_llc.c:501
__sys_connect_file net/socket.c:1933 [inline]
__sys_connect+0x3cb/0x450 net/socket.c:1950
__do_sys_connect net/socket.c:1960 [inline]
__se_sys_connect net/socket.c:1957 [inline]
__x64_sys_connect+0x76/0x80 net/socket.c:1957
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
Freed by task 4228:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
kasan_slab_free include/linux/kasan.h:230 [inline]
slab_free_hook mm/slub.c:1710 [inline]
slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
slab_free mm/slub.c:3504 [inline]
kmem_cache_free_bulk+0x38b/0x490 mm/slub.c:3645
kfree_bulk include/linux/slab.h:465 [inline]
kfree_rcu_work+0x311/0x900 kernel/rcu/tree.c:3299
process_one_work+0x867/0xff0 kernel/workqueue.c:2310
worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
kthread+0x42e/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
Last potentially related work creation:
kasan_save_stack+0x35/0x60 mm/kasan/common.c:38
kasan_record_aux_stack+0xb8/0x100 mm/kasan/generic.c:348
kvfree_call_rcu+0x105/0x7f0 kernel/rcu/tree.c:3600
llc_sap_put include/net/llc.h:132 [inline]
llc_ui_release+0x212/0x450 net/llc/af_llc.c:223
__sock_release net/socket.c:651 [inline]
sock_close+0xbf/0x210 net/socket.c:1346
__fput+0x212/0x8c0 fs/file_table.c:311
task_work_run+0x125/0x1a0 kernel/task_work.c:188
get_signal+0x123e/0x12e0 kernel/signal.c:2681
arch_do_signal_or_restart+0xe6/0x12a0 arch/x86/kernel/signal.c:867
handle_signal_work kernel/entry/common.c:154 [inline]
exit_to_user_mode_loop+0x9e/0x130 kernel/entry/common.c:178
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
Second to last potentially related work creation:
kasan_save_stack+0x35/0x60 mm/kasan/common.c:38
kasan_record_aux_stack+0xb8/0x100 mm/kasan/generic.c:348
__call_rcu kernel/rcu/tree.c:3011 [inline]
call_rcu+0x189/0x900 kernel/rcu/tree.c:3091
netlink_release+0x134c/0x1790 net/netlink/af_netlink.c:795
__sock_release net/socket.c:651 [inline]
sock_close+0xbf/0x210 net/socket.c:1346
__fput+0x212/0x8c0 fs/file_table.c:311
task_work_run+0x125/0x1a0 kernel/task_work.c:188
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:181
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
The buggy address belongs to the object at ffff88801d993000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 16 bytes inside of
2048-byte region [ffff88801d993000, ffff88801d993800)
The buggy address belongs to the page:
page:ffffea0000766400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1d990
head:ffffea0000766400 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 0000000100000001 ffff888016c42000
raw: 0000000000000000 0000000080080008 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 4186, ts 67578897582, free_ts 67563566426
prep_new_page mm/page_alloc.c:2426 [inline]
get_page_from_freelist+0x24f6/0x2670 mm/page_alloc.c:4192
__alloc_pages+0x1ee/0x480 mm/page_alloc.c:5501
alloc_slab_page mm/slub.c:1780 [inline]
allocate_slab mm/slub.c:1917 [inline]
new_slab+0xc0/0x4b0 mm/slub.c:1980
___slab_alloc+0x807/0xdd0 mm/slub.c:3013
__slab_alloc mm/slub.c:3100 [inline]
slab_alloc_node mm/slub.c:3191 [inline]
slab_alloc mm/slub.c:3233 [inline]
kmem_cache_alloc_trace+0xf9/0x290 mm/slub.c:3250
kmalloc include/linux/slab.h:607 [inline]
kzalloc include/linux/slab.h:738 [inline]
ipv6_add_dev+0xce/0x11a0 net/ipv6/addrconf.c:384
addrconf_notify+0x66f/0xf20 net/ipv6/addrconf.c:3586
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:391
call_netdevice_notifiers_extack net/core/dev.c:2074 [inline]
call_netdevice_notifiers net/core/dev.c:2088 [inline]
register_netdevice+0x12a8/0x1720 net/core/dev.c:10454
cfg80211_register_netdevice+0x155/0x2f0 net/wireless/core.c:1424
ieee80211_if_add+0x1002/0x1e00 net/mac80211/iface.c:2078
ieee80211_register_hw+0x2b39/0x3a60 net/mac80211/main.c:1323
mac80211_hwsim_new_radio+0x209d/0x4050 drivers/net/wireless/mac80211_hwsim.c:3373
hwsim_new_radio_nl+0xa7d/0xc50 drivers/net/wireless/mac80211_hwsim.c:3949
genl_family_rcv_msg_doit net/netlink/genetlink.c:731 [inline]
genl_family_rcv_msg net/netlink/genetlink.c:775 [inline]
genl_rcv_msg+0xd0b/0xfa0 net/netlink/genetlink.c:792
netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2519
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1340 [inline]
free_pcp_prepare mm/page_alloc.c:1391 [inline]
free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
free_unref_page+0x8f/0x2a0 mm/page_alloc.c:3396
free_slab mm/slub.c:2020 [inline]
discard_slab mm/slub.c:2026 [inline]
__unfreeze_partials+0x188/0x1e0 mm/slub.c:2512
put_cpu_partial+0x12d/0x190 mm/slub.c:2592
qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
__kasan_slab_alloc+0x2f/0xc0 mm/kasan/common.c:444
kasan_slab_alloc include/linux/kasan.h:254 [inline]
slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
slab_alloc_node mm/slub.c:3225 [inline]
__kmalloc_node+0x1ae/0x3a0 mm/slub.c:4456
kmalloc_array_node include/linux/slab.h:700 [inline]
kcalloc_node include/linux/slab.h:705 [inline]
memcg_alloc_page_obj_cgroups+0x7d/0x120 mm/memcontrol.c:2839
account_slab_page mm/slab.h:424 [inline]
allocate_slab mm/slub.c:1933 [inline]
new_slab+0x100/0x4b0 mm/slub.c:1980
___slab_alloc+0x807/0xdd0 mm/slub.c:3013
__slab_alloc mm/slub.c:3100 [inline]
slab_alloc_node mm/slub.c:3191 [inline]
slab_alloc mm/slub.c:3233 [inline]
kmem_cache_alloc+0xf0/0x280 mm/slub.c:3238
alloc_inode fs/inode.c:263 [inline]
new_inode_pseudo+0x77/0x210 fs/inode.c:1001
new_inode+0x25/0x1d0 fs/inode.c:1030
debugfs_get_inode fs/debugfs/inode.c:72 [inline]
__debugfs_create_file+0x147/0x500 fs/debugfs/inode.c:409
Memory state around the buggy address:
ffff88801d992f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88801d992f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801d993000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88801d993080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88801d993100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess):
0: 83 c7 18 add $0x18,%edi
3: be ff ff ff ff mov $0xffffffff,%esi
8: e8 6e cb 6b 08 call 0x86bcb7b
d: 85 c0 test %eax,%eax
f: 74 46 je 0x57
11: 4d 85 ff test %r15,%r15
14: 75 62 jne 0x78
16: e9 06 01 00 00 jmp 0x121
1b: 48 89 df mov %rbx,%rdi
1e: e8 98 3a 75 08 call 0x8753abb
23: e8 43 d7 2a 00 call 0x2ad76b
28: fb sti
29: 5b pop %rbx
* 2a: 41 5c pop %r12 <-- trapping instruction
2c: 41 5d pop %r13
2e: 41 5e pop %r14
30: 41 5f pop %r15
32: 5d pop %rbp
33: c3 ret
34: 48 89 df mov %rbx,%rdi
37: e8 2f 0e fe ff call 0xfffe0e6b
3c: 43 rex.XB
3d: 80 .byte 0x80
3e: 3c 2c cmp $0x2c,%al
Struck through repros no longer work on HEAD.