syzbot
KASAN: slab-use-after-free Read in llc_conn_ac_send_sabme_cmd_p_set_x
Status:
upstream: reported on 2026/07/15 15:55
Subsystems:
net
Labels:
prio:normal
[Documentation on labels]
Reported-by: syzbot+44efda9647c52be29d9c@syzkaller.appspotmail.com
First crash: 12d, last: 1h00m
Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in llc_conn_ac_send_sabme_cmd_p_set_x+0x442/0x470 net/llc/llc_c_ac.c:782
Read of size 1 at addr ffff888031928010 by task syz.0.3853/22514
CPU: 0 UID: 0 PID: 22514 Comm: syz.0.3853 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0x13d/0x4b0 mm/kasan/report.c:482
kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
llc_conn_ac_send_sabme_cmd_p_set_x+0x442/0x470 net/llc/llc_c_ac.c:782
llc_exec_conn_trans_actions net/llc/llc_conn.c:437 [inline]
llc_conn_service net/llc/llc_conn.c:362 [inline]
llc_conn_state_process+0x3ec/0x1480 net/llc/llc_conn.c:66
llc_process_tmr_ev net/llc/llc_c_ac.c:1442 [inline]
llc_conn_tmr_common_cb+0x2d4/0x880 net/llc/llc_c_ac.c:1325
call_timer_fn+0x19a/0x610 kernel/time/timer.c:1748
expire_timers kernel/time/timer.c:1799 [inline]
__run_timers+0x757/0xb00 kernel/time/timer.c:2374
__run_timer_base kernel/time/timer.c:2386 [inline]
__run_timer_base kernel/time/timer.c:2378 [inline]
run_timer_base+0x114/0x190 kernel/time/timer.c:2395
run_timer_softirq+0x1a/0x50 kernel/time/timer.c:2405
handle_softirqs+0x1ea/0x9b0 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0x162/0x210 kernel/softirq.c:735
irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
sysvec_apic_timer_interrupt+0xa3/0xc0 arch/x86/kernel/apic/apic.c:1062
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:preempt_schedule_irq+0x4b/0x90 kernel/sched/core.c:7556
Code: 00 00 00 fc ff df 48 89 eb 48 c1 eb 03 48 01 d3 f6 c4 02 75 47 bf 01 00 00 00 e8 d0 b2 19 f6 e8 eb a6 56 f6 fb bf 01 00 00 00 <e8> a0 91 ff ff 9c 58 fa f6 c4 02 75 1e bf 01 00 00 00 e8 be 52 19
RSP: 0000:ffffc9000ea17748 EFLAGS: 00000206
RAX: 000000000001764d RBX: ffffed1005deb950 RCX: 0000000000000040
RDX: 0000000000000000 RSI: ffffffff8e1a4e62 RDI: 0000000000000001
RBP: ffff88802ef5ca80 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
irqentry_exit_to_kernel_mode_preempt include/linux/irq-entry-common.h:468 [inline]
irqentry_exit_to_kernel_mode include/linux/irq-entry-common.h:539 [inline]
irqentry_exit+0x205/0xa00 kernel/entry/common.c:167
asm_sysvec_call_function_single+0x1a/0x20 arch/x86/include/asm/idtentry.h:681
RIP: 0010:llc_exec_sap_trans_actions net/llc/llc_sap.c:147 [inline]
RIP: 0010:llc_sap_next_state net/llc/llc_sap.c:176 [inline]
RIP: 0010:llc_sap_state_process+0x241/0x570 net/llc/llc_sap.c:203
Code: 49 be 00 00 00 00 00 fc ff df 48 8b 04 24 4c 8b 60 10 4d 85 e4 75 2f eb 5f e8 2b c3 5c f8 48 89 ee 4c 89 ef 2e 2e 2e 41 ff d7 <31> ff 41 89 c7 89 c6 e8 83 bd 5c f8 31 c0 45 85 ff 0f 95 c0 09 c3
RSP: 0000:ffffc9000ea17850 EFLAGS: 00000246
RAX: 0000000000000002 RBX: 0000000000000000 RCX: ffffc9000ef3c000
RDX: 0000000000080000 RSI: ffffffff89ad38f0 RDI: ffffffff8c401480
RBP: ffff88805566f8c0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff8d1aabc0
R13: ffff888034e25000 R14: dffffc0000000000 R15: ffffffff89ad3bd0
llc_ui_sendmsg+0xddc/0x1540 net/llc/af_llc.c:997
sock_sendmsg_nosec net/socket.c:775 [inline]
__sock_sendmsg net/socket.c:790 [inline]
____sys_sendmsg+0xa4d/0xbe0 net/socket.c:2684
___sys_sendmsg+0x190/0x1e0 net/socket.c:2738
__sys_sendmmsg+0x20c/0x440 net/socket.c:2827
__do_sys_sendmmsg net/socket.c:2854 [inline]
__se_sys_sendmmsg net/socket.c:2851 [inline]
__x64_sys_sendmmsg+0x9c/0x100 net/socket.c:2851
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1e0cd9de99
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:00007f1e0afb4028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f1e0d026180 RCX: 00007f1e0cd9de99
RDX: 03fffffffffffeed RSI: 0000200000001380 RDI: 0000000000000008
RBP: 00007f1e0ce33eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1e0d026218 R14: 00007f1e0d026180 R15: 00007ffe645e1848
</TASK>
Allocated by task 22491:
kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__kmalloc_cache_noprof+0x2e5/0x6c0 mm/slub.c:5515
_kmalloc_noprof include/linux/slab.h:969 [inline]
_kzalloc_noprof include/linux/slab.h:1290 [inline]
llc_sap_alloc net/llc/llc_core.c:29 [inline]
llc_sap_open+0x120/0x3b0 net/llc/llc_core.c:96
llc_ui_autobind.isra.0+0x2ae/0x580 net/llc/af_llc.c:301
llc_ui_connect+0x582/0xdb0 net/llc/af_llc.c:498
__sys_connect_file+0x141/0x1a0 net/socket.c:2135
__sys_connect+0x141/0x170 net/socket.c:2154
__do_sys_connect net/socket.c:2160 [inline]
__se_sys_connect net/socket.c:2157 [inline]
__x64_sys_connect+0x72/0xb0 net/socket.c:2157
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 0:
kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2705 [inline]
__rcu_free_sheaf_prepare+0x5d/0x2f0 mm/slub.c:2956
rcu_free_sheaf+0x1a/0xe0 mm/slub.c:6004
rcu_do_batch kernel/rcu/tree.c:2645 [inline]
rcu_core+0x5a2/0x10d0 kernel/rcu/tree.c:2897
handle_softirqs+0x1ea/0x9b0 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0x162/0x210 kernel/softirq.c:735
irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
sysvec_apic_timer_interrupt+0xa3/0xc0 arch/x86/kernel/apic/apic.c:1062
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
The buggy address belongs to the object at ffff888031928000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 16 bytes inside of
freed 2048-byte region [ffff888031928000, ffff888031928800)
The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88803192a000 pfn:0x31928
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000240(workingset|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000240 ffff88813fe23000 ffffea0001e5e410 ffffea0000dc8010
raw: ffff88803192a000 0000000800080007 00000000f5000000 0000000000000000
head: 00fff00000000240 ffff88813fe23000 ffffea0001e5e410 ffffea0000dc8010
head: ffff88803192a000 0000000800080007 00000000f5000000 0000000000000000
head: 00fff00000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 18267995081, free_ts 0
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1859
prep_new_page mm/page_alloc.c:1867 [inline]
get_page_from_freelist+0xf48/0x3530 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x299/0x2dc0 mm/page_alloc.c:5304
alloc_slab_page mm/slub.c:3294 [inline]
allocate_slab mm/slub.c:3408 [inline]
new_slab+0xa2/0x650 mm/slub.c:3454
refill_objects+0xe3/0x410 mm/slub.c:7338
refill_sheaf mm/slub.c:2832 [inline]
__pcs_replace_empty_main+0x376/0x680 mm/slub.c:4703
alloc_from_pcs mm/slub.c:4801 [inline]
slab_alloc_node mm/slub.c:4933 [inline]
__kmalloc_cache_noprof+0x479/0x6c0 mm/slub.c:5511
_kmalloc_noprof include/linux/slab.h:969 [inline]
_kzalloc_noprof include/linux/slab.h:1290 [inline]
__media_device_register+0x50/0x470 drivers/media/mc/mc-device.c:740
vivid_create_devnodes drivers/media/test-drivers/vivid/vivid-core.c:1749 [inline]
vivid_create_instance drivers/media/test-drivers/vivid/vivid-core.c:2042 [inline]
vivid_probe.cold+0x8835/0x921e drivers/media/test-drivers/vivid/vivid-core.c:2095
platform_probe+0x106/0x1d0 drivers/base/platform.c:1439
call_driver_probe drivers/base/dd.c:628 [inline]
really_probe+0x241/0xa60 drivers/base/dd.c:706
__driver_probe_device+0x20e/0x450 drivers/base/dd.c:868
driver_probe_device+0x4a/0x140 drivers/base/dd.c:898
__driver_attach+0x21f/0x5b0 drivers/base/dd.c:1292
bus_for_each_dev+0x13e/0x1d0 drivers/base/bus.c:383
bus_add_driver+0x305/0x5b0 drivers/base/bus.c:763
page_owner free stack trace missing
Memory state around the buggy address:
ffff888031927f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888031927f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888031928000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888031928080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888031928100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess):
0: 00 00 add %al,(%rax)
2: 00 fc add %bh,%ah
4: ff lcall (bad)
5: df 48 89 fisttps -0x77(%rax)
8: eb 48 jmp 0x52
a: c1 eb 03 shr $0x3,%ebx
d: 48 01 d3 add %rdx,%rbx
10: f6 c4 02 test $0x2,%ah
13: 75 47 jne 0x5c
15: bf 01 00 00 00 mov $0x1,%edi
1a: e8 d0 b2 19 f6 call 0xf619b2ef
1f: e8 eb a6 56 f6 call 0xf656a70f
24: fb sti
25: bf 01 00 00 00 mov $0x1,%edi
* 2a: e8 a0 91 ff ff call 0xffff91cf <-- trapping instruction
2f: 9c pushf
30: 58 pop %rax
31: fa cli
32: f6 c4 02 test $0x2,%ah
35: 75 1e jne 0x55
37: bf 01 00 00 00 mov $0x1,%edi
3c: e8 .byte 0xe8
3d: be .byte 0xbe
3e: 52 push %rdx
3f: 19 .byte 0x19
Struck through repros no longer work on HEAD.