syzbot
KASAN: use-after-free Read in llc_conn_ac_send_sabme_cmd_p_set_x
Status:
upstream: reported syz repro on 2026/07/25 04:49
Reported-by: syzbot+11738dbec49b83acb18b@syzkaller.appspotmail.com
First crash: 57d, last: 8d05h
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 ffff888079827010 by task swapper/0/0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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:default_idle+0xb/0x10 arch/x86/kernel/process.c:730
Code: b7 48 89 df e8 56 8f f4 f7 eb ad e8 4f ab f6 ff 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 00 cc 66 90 0f 00 2d b7 25 5c 00 fb f4 <c3> 0f 1f 40 00 41 57 41 56 53 49 be 00 00 00 00 00 fc ff df 65 48
RSP: 0018:ffffffff8c007dc8 EFLAGS: 000002c6
RAX: 4f653d092fd3d400 RBX: ffffffff8c0bc480 RCX: 4f653d092fd3d400
RDX: 0000000000000001 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a43c0
RBP: ffffffff8c007ef8 R08: ffff8880b903b30b R09: 1ffff11017207661
R10: dffffc0000000000 R11: ffffed1017207662 R12: 1ffffffff1800fc4
R13: dffffc0000000000 R14: 1ffffffff1817890 R15: 0000000000000000
default_idle_call+0x81/0xc0 kernel/sched/idle.c:112
cpuidle_idle_call kernel/sched/idle.c:202 [inline]
do_idle+0x3a1/0x650 kernel/sched/idle.c:326
cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:424
start_kernel+0x489/0x540 init/main.c:1114
secondary_startup_64_no_verify+0xb1/0xbb
</TASK>
Allocated by task 6500:
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 4285:
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
in6_dev_put include/net/addrconf.h:389 [inline]
addrconf_ifdown+0x1778/0x19f0 net/ipv6/addrconf.c:3941
addrconf_notify+0x445/0xf20 net/ipv6/addrconf.c:-1
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]
unregister_netdevice_many+0x109b/0x1a40 net/core/dev.c:11160
ip_tunnel_delete_nets+0x326/0x370 net/ipv4/ip_tunnel.c:1137
ops_exit_list net/core/net_namespace.c:177 [inline]
cleanup_net+0x78e/0xba0 net/core/net_namespace.c:635
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
The buggy address belongs to the object at ffff888079827000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 16 bytes inside of
2048-byte region [ffff888079827000, ffff888079827800)
The buggy address belongs to the page:
page:ffffea0001e60800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x79820
head:ffffea0001e60800 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888016c42000
raw: 0000000000000000 0000000000080008 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 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 4318, ts 79078794024, free_ts 79064145392
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]
__kmalloc_node_track_caller+0x13d/0x3a0 mm/slub.c:4963
kmalloc_reserve net/core/skbuff.c:356 [inline]
pskb_expand_head+0x128/0x1100 net/core/skbuff.c:1710
netlink_trim+0x180/0x220 net/netlink/af_netlink.c:1295
netlink_broadcast_filtered+0x69/0x1170 net/netlink/af_netlink.c:1512
netlink_broadcast net/netlink/af_netlink.c:1557 [inline]
nlmsg_multicast include/net/netlink.h:1044 [inline]
nlmsg_notify+0xdf/0x190 net/netlink/af_netlink.c:2562
__dev_notify_flags+0xdc/0x300 net/core/dev.c:8913
dev_change_flags+0xda/0x1a0 net/core/dev.c:8955
do_setlink+0xca4/0x29d0 net/core/rtnetlink.c:2793
__rtnl_newlink net/core/rtnetlink.c:3464 [inline]
rtnl_newlink+0x15bb/0x1920 net/core/rtnetlink.c:3586
rtnetlink_rcv_msg+0x7f1/0xf10 net/core/rtnetlink.c:5698
netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2519
netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
netlink_unicast+0x78f/0x940 net/netlink/af_netlink.c:1340
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]
kmem_cache_alloc_node+0x184/0x2c0 mm/slub.c:3261
__alloc_skb+0xf4/0x750 net/core/skbuff.c:415
alloc_skb include/linux/skbuff.h:1162 [inline]
netlink_alloc_large_skb net/netlink/af_netlink.c:1178 [inline]
netlink_sendmsg+0x654/0xbe0 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec net/socket.c:706 [inline]
__sock_sendmsg net/socket.c:718 [inline]
____sys_sendmsg+0x5be/0x8f0 net/socket.c:2446
___sys_sendmsg+0x236/0x2e0 net/socket.c:2500
__sys_sendmsg net/socket.c:2529 [inline]
__do_sys_sendmsg net/socket.c:2538 [inline]
__se_sys_sendmsg+0x1b7/0x2a0 net/socket.c:2536
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
Memory state around the buggy address:
ffff888079826f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888079826f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888079827000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888079827080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888079827100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess):
0: b7 48 mov $0x48,%bh
2: 89 df mov %ebx,%edi
4: e8 56 8f f4 f7 call 0xf7f48f5f
9: eb ad jmp 0xffffffb8
b: e8 4f ab f6 ff call 0xfff6ab5f
10: 00 00 add %al,(%rax)
12: cc int3
13: cc int3
14: 00 00 add %al,(%rax)
16: cc int3
17: cc int3
18: 00 00 add %al,(%rax)
1a: cc int3
1b: cc int3
1c: 00 00 add %al,(%rax)
1e: cc int3
1f: 66 90 xchg %ax,%ax
21: 0f 00 2d b7 25 5c 00 verw 0x5c25b7(%rip) # 0x5c25df
28: fb sti
29: f4 hlt
* 2a: c3 ret <-- trapping instruction
2b: 0f 1f 40 00 nopl 0x0(%rax)
2f: 41 57 push %r15
31: 41 56 push %r14
33: 53 push %rbx
34: 49 be 00 00 00 00 00 movabs $0xdffffc0000000000,%r14
3b: fc ff df
3e: 65 gs
3f: 48 rex.W
Struck through repros no longer work on HEAD.