[syzbot] [net?] KASAN: slab-use-after-free Read in llc_conn_ac_send_sabme_cmd_p_set_x

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a13c140cc289 Linux 7.2-rc3
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=144c3b89580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d69870d5e052935f
dashboard link: https://syzkaller.appspot.com/bug?extid=44efda9647c52be29d9c
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2052a80016f0/disk-a13c140c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0d06ec9d98a4/vmlinux-a13c140c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8cfe7c92eaf6/bzImage-a13c140c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+44efda...@syzkaller.appspotmail.com

==================================================================
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 ffff8880370c8010 by task kworker/u8:0/11804

CPU: 0 UID: 0 PID: 11804 Comm: kworker/u8:0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/10/2026
Workqueue: events_unbound toggle_allocation_gate
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:finish_task_switch.isra.0+0x2cd/0x10c0 kernel/sched/core.c:5361
Code: ab 0a 00 00 41 c7 87 20 0e 00 00 00 00 00 00 e9 47 04 00 00 49 8d 7f 48 e8 30 b4 e6 09 e8 1b a9 3c 00 fb 48 8d bb f8 16 00 00 <48> b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 0f b6 04 02 84
RSP: 0018:ffffc90005097578 EFLAGS: 00000202
RAX: 0000000000056db3 RBX: ffff8880741c8000 RCX: 0000000000000040
RDX: 0000000000000000 RSI: ffffffff8e1a3c59 RDI: ffff8880741c96f8
RBP: ffffc900050975d0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff8e891480
R13: 0000000000000001 R14: ffffffff91227064 R15: ffff8880b843b4c0
context_switch kernel/sched/core.c:5513 [inline]
__schedule+0x1264/0x6730 kernel/sched/core.c:7234
preempt_schedule_irq+0x50/0x90 kernel/sched/core.c:7556
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_reschedule_ipi+0x1a/0x20 arch/x86/include/asm/idtentry.h:679
RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x70 kernel/kcov.c:210
Code: 56 e1 5e 00 48 89 df 5b e9 9d 5c 64 00 be 03 00 00 00 5b e9 32 5a 13 03 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <f3> 0f 1e fa 65 8b 05 85 a3 59 12 48 8b 34 24 65 48 8b 15 61 a3 59
RSP: 0018:ffffc90005097850 EFLAGS: 00000206
RAX: 0000000000000000 RBX: ffffc900050979b0 RCX: ffffffff8bb86f00
RDX: 0000000000008000 RSI: 0000000000000000 RDI: ffff8880741c8000
RBP: ffffc900050979d4 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000008000 R11: 0000000000000000 R12: ffffc900050979fc
R13: 0000000000008000 R14: 0000000000008000 R15: 0000000000000ffa
insn_get_modrm+0xee/0x790 arch/x86/lib/insn.c:396
insn_get_sib arch/x86/lib/insn.c:466 [inline]
insn_get_displacement+0x2f9/0x960 arch/x86/lib/insn.c:507
insn_get_immediate+0x84/0x1e00 arch/x86/lib/insn.c:673
insn_get_length arch/x86/lib/insn.c:745 [inline]
insn_decode+0x21d/0x320 arch/x86/lib/insn.c:784
__smp_text_poke_batch_add+0x174/0x790 arch/x86/kernel/alternative.c:3103
arch_jump_label_transform_queue+0xaf/0x120 arch/x86/kernel/jump_label.c:138
__jump_label_update+0xd7/0x380 kernel/jump_label.c:513
jump_label_update+0x37a/0x550 kernel/jump_label.c:910
static_key_disable_cpuslocked+0x162/0x1c0 kernel/jump_label.c:240
static_key_disable+0x1a/0x20 kernel/jump_label.c:248
toggle_allocation_gate mm/kfence/core.c:918 [inline]
toggle_allocation_gate+0x149/0x2d0 mm/kfence/core.c:903
process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
process_scheduled_works kernel/workqueue.c:3405 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 12543:
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_call_function_single arch/x86/kernel/smp.c:267 [inline]
sysvec_call_function_single+0xa3/0xc0 arch/x86/kernel/smp.c:267
asm_sysvec_call_function_single+0x1a/0x20 arch/x86/include/asm/idtentry.h:681

The buggy address belongs to the object at ffff8880370c8000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 16 bytes inside of
freed 2048-byte region [ffff8880370c8000, ffff8880370c8800)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff8880370cd000 pfn:0x370c8
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 ffff88813fe22000 ffffea0000c73e10 ffffea0000a2e810
raw: ffff8880370cd000 0000000800080007 00000000f5000000 0000000000000000
head: 00fff00000000240 ffff88813fe22000 ffffea0000c73e10 ffffea0000a2e810
head: ffff8880370cd000 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 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5615, tgid 5615 (syz-executor), ts 66637688496, free_ts 48968356257
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]
__do_kmalloc_node mm/slub.c:5361 [inline]
__kmalloc_node_track_caller_noprof+0x679/0x830 mm/slub.c:5497
kmalloc_reserve+0xe8/0x350 net/core/skbuff.c:637
pskb_expand_head+0x249/0x10e0 net/core/skbuff.c:2306
netlink_trim+0x22d/0x2f0 net/netlink/af_netlink.c:1300
netlink_broadcast_filtered+0x6d/0xf20 net/netlink/af_netlink.c:1518
nlmsg_multicast_filtered include/net/netlink.h:1165 [inline]
nlmsg_multicast include/net/netlink.h:1184 [inline]
nlmsg_notify+0xb1/0x290 net/netlink/af_netlink.c:2599
rtnl_notify net/core/rtnetlink.c:963 [inline]
rtmsg_ifinfo_send net/core/rtnetlink.c:4553 [inline]
rtmsg_ifinfo_event net/core/rtnetlink.c:4569 [inline]
rtmsg_ifinfo_event net/core/rtnetlink.c:4556 [inline]
rtmsg_ifinfo+0x177/0x1b0 net/core/rtnetlink.c:4575
__dev_notify_flags+0x24c/0x2e0 net/core/dev.c:9789
rtnl_configure_link+0x1b5/0x280 net/core/rtnetlink.c:3679
rtnl_newlink_create net/core/rtnetlink.c:3923 [inline]
__rtnl_newlink net/core/rtnetlink.c:4044 [inline]
rtnl_newlink+0x153b/0x2380 net/core/rtnetlink.c:4159
page last free pid 5271 tgid 5271 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1406 [inline]
__free_frozen_pages+0x79f/0x1090 mm/page_alloc.c:2950
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x47/0xf0 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x1a0/0x1f0 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:350
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4612 [inline]
slab_alloc_node mm/slub.c:4945 [inline]
kmem_cache_alloc_node_noprof+0x27d/0x6b0 mm/slub.c:5017
__alloc_skb+0x140/0x710 net/core/skbuff.c:704
alloc_skb include/linux/skbuff.h:1384 [inline]
alloc_skb_with_frags+0xdd/0x760 net/core/skbuff.c:6769
sock_alloc_send_pskb+0x801/0x980 net/core/sock.c:3010
unix_dgram_sendmsg+0x3c7/0x1810 net/unix/af_unix.c:2136
unix_seqpacket_sendmsg+0x12a/0x1d0 net/unix/af_unix.c:2537
sock_sendmsg_nosec net/socket.c:775 [inline]
__sock_sendmsg net/socket.c:790 [inline]
sock_write_iter+0x53a/0x5b0 net/socket.c:1241
do_iter_readv_writev+0x6f7/0x930 fs/read_write.c:828
vfs_writev+0x360/0xdd0 fs/read_write.c:1058
do_writev+0x28a/0x340 fs/read_write.c:1104
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

Memory state around the buggy address:
ffff8880370c7f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880370c7f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880370c8000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880370c8080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880370c8100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess), 2 bytes skipped:
0: 00 00 add %al,(%rax)
2: 41 c7 87 20 0e 00 00 movl $0x0,0xe20(%r15)
9: 00 00 00 00
d: e9 47 04 00 00 jmp 0x459
12: 49 8d 7f 48 lea 0x48(%r15),%rdi
16: e8 30 b4 e6 09 call 0x9e6b44b
1b: e8 1b a9 3c 00 call 0x3ca93b
20: fb sti
21: 48 8d bb f8 16 00 00 lea 0x16f8(%rbx),%rdi
* 28: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax <-- trapping instruction
2f: fc ff df
32: 48 89 fa mov %rdi,%rdx
35: 48 c1 ea 03 shr $0x3,%rdx
39: 0f b6 04 02 movzbl (%rdx,%rax,1),%eax
3d: 84 .byte 0x84


---
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 syzk...@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