[syzbot] [hams?] KASAN: slab-use-after-free Read in ax25cmp (2)

syzbot
2026-03-31T19:19:25Z

Hello,

syzbot found the following issue on:

HEAD commit: 7aaa8047eafd Linux 7.0-rc6
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11f71a48580000
kernel config: https://syzkaller.appspot.com/x/.config?x=5a3e5e8c17cc174e
dashboard link: https://syzkaller.appspot.com/bug?extid=abd2b69348e2d9b107a1
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/4e96235a659c/disk-7aaa8047.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2dbf138efd1a/vmlinux-7aaa8047.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c0528de45bad/bzImage-7aaa8047.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+abd2b69348e2d9b107a1@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in ax25cmp+0x17b/0x1d0 net/ax25/ax25_addr.c:119
Read of size 1 at addr ffff8880589bdc08 by task syz-executor/30916

CPU: 1 UID: 0 PID: 30916 Comm: syz-executor Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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+0x156/0x4c9 mm/kasan/report.c:482
kasan_report+0xdf/0x1e0 mm/kasan/report.c:595
ax25cmp+0x17b/0x1d0 net/ax25/ax25_addr.c:119
ax25_find_cb+0x142/0x410 net/ax25/af_ax25.c:236
ax25_send_frame+0x157/0xb70 net/ax25/ax25_out.c:55
rose_send_frame+0xfa/0x2a0 net/rose/rose_link.c:106
rose_transmit_restart_request+0x1b8/0x250 net/rose/rose_link.c:198
rose_t0timer_expiry+0x1d/0x150 net/rose/rose_link.c:83
call_timer_fn+0x19a/0x670 kernel/time/timer.c:1748
expire_timers kernel/time/timer.c:1799 [inline]
__run_timers+0x757/0xb30 kernel/time/timer.c:2373
__run_timer_base kernel/time/timer.c:2385 [inline]
__run_timer_base kernel/time/timer.c:2377 [inline]
run_timer_base+0x114/0x190 kernel/time/timer.c:2394
run_timer_softirq+0x1a/0x50 kernel/time/timer.c:2404
handle_softirqs+0x1eb/0x9e0 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0xef/0x150 kernel/softirq.c:723
irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
sysvec_apic_timer_interrupt+0xa3/0xc0 arch/x86/kernel/apic/apic.c:1056
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:preempt_schedule_irq+0x4b/0x90 kernel/sched/core.c:7238
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 80 b8 43 f6 e8 3b ce 7e f6 fb bf 01 00 00 00 <e8> e0 96 ff ff 9c 58 fa f6 c4 02 75 1e bf 01 00 00 00 e8 9e 56 43
RSP: 0018:ffffc90002ea7838 EFLAGS: 00000202
RAX: 0000000000051bfd RBX: ffffed101344f000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8de79d93 RDI: 0000000000000001
RBP: ffff88809a278000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
irqentry_exit+0x17b/0x670 kernel/entry/common.c:239
asm_sysvec_reschedule_ipi+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:lock_acquire+0x5e/0x380 kernel/locking/lockdep.c:5872
Code: 05 bb 36 29 12 83 f8 07 0f 87 f0 00 00 00 48 0f a3 05 86 bc f4 0e 0f 82 c2 02 00 00 8b 35 6e f0 f4 0e 85 f6 0f 85 dd 00 00 00 <48> 8b 44 24 30 65 48 2b 05 5d 36 29 12 0f 85 02 03 00 00 48 83 c4
RSP: 0018:ffffc90002ea7938 EFLAGS: 00000206
RAX: 0000000000000046 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8de53c03 RDI: ffffffff8c1b1a20
RBP: ffffffff8e7e7920 R08: 0000000086db7919 R09: 0000000000000007
R10: 0000000000000200 R11: 0000000000000000 R12: 0000000000000002
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
rcu_lock_acquire include/linux/rcupdate.h:312 [inline]
rcu_read_lock include/linux/rcupdate.h:850 [inline]
class_rcu_constructor include/linux/rcupdate.h:1193 [inline]
unwind_next_frame+0xd1/0x1ea0 arch/x86/kernel/unwind_orc.c:495
arch_stack_walk+0x94/0xf0 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x8e/0xc0 kernel/stacktrace.c:122
kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
unpoison_slab_object mm/kasan/common.c:340 [inline]
__kasan_slab_alloc+0x89/0x90 mm/kasan/common.c:366
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4538 [inline]
slab_alloc_node mm/slub.c:4866 [inline]
kmem_cache_alloc_noprof+0x241/0x6e0 mm/slub.c:4873
alloc_filename fs/namei.c:142 [inline]
do_getname+0x35/0x390 fs/namei.c:182
getname_flags fs/namei.c:225 [inline]
class_filename_flags_constructor include/linux/fs.h:2541 [inline]
user_path_at+0x26/0x60 fs/namei.c:3617
ksys_umount fs/namespace.c:2062 [inline]
__do_sys_umount fs/namespace.c:2070 [inline]
__se_sys_umount fs/namespace.c:2068 [inline]
__x64_sys_umount+0x10a/0x1a0 fs/namespace.c:2068
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f502359da57
Code: a2 c7 05 9c fc 24 00 00 00 00 00 eb 96 e8 e1 12 00 00 90 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007ffc8bc59ed8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: ffffffffffffffda RBX: 00007f5023632048 RCX: 00007f502359da57
RDX: 0000000000000004 RSI: 0000000000000009 RDI: 00007ffc8bc5b020
RBP: 00007ffc8bc5b00c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffc8bc5b020
R13: 00007f5023632048 R14: 00000000001c31ca R15: 00007ffc8bc5b060
</TASK>

Allocated by task 15931:
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
kmalloc_noprof include/linux/slab.h:950 [inline]
rose_add_node net/rose/rose_route.c:85 [inline]
rose_rt_ioctl+0x586/0x2550 net/rose/rose_route.c:748
rose_ioctl+0x491/0x7d0 net/rose/af_rose.c:1387
sock_do_ioctl+0x118/0x280 net/socket.c:1254
sock_ioctl+0x599/0x6b0 net/socket.c:1375
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 31660:
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:2685 [inline]
slab_free mm/slub.c:6165 [inline]
kfree+0x1f6/0x6b0 mm/slub.c:6483
rose_neigh_put include/net/rose.h:166 [inline]
rose_timer_expiry+0x53f/0x630 net/rose/rose_timer.c:183
call_timer_fn+0x19a/0x670 kernel/time/timer.c:1748
expire_timers kernel/time/timer.c:1799 [inline]
__run_timers+0x757/0xb30 kernel/time/timer.c:2373
__run_timer_base kernel/time/timer.c:2385 [inline]
__run_timer_base kernel/time/timer.c:2377 [inline]
run_timer_base+0x114/0x190 kernel/time/timer.c:2394
run_timer_softirq+0x1a/0x50 kernel/time/timer.c:2404
handle_softirqs+0x1eb/0x9e0 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0xef/0x150 kernel/softirq.c:723
irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
sysvec_apic_timer_interrupt+0xa3/0xc0 arch/x86/kernel/apic/apic.c:1056
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697

The buggy address belongs to the object at ffff8880589bdc00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 8 bytes inside of
freed 512-byte region [ffff8880589bdc00, ffff8880589bde00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff8880589bf400 pfn:0x589bc
head: order:2 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 ffff88813fe40c80 ffffea0001f2ac10 ffffea0001e4cd10
raw: ffff8880589bf400 000000080010000d 00000000f5000000 0000000000000000
head: 00fff00000000240 ffff88813fe40c80 ffffea0001f2ac10 ffffea0001e4cd10
head: ffff8880589bf400 000000080010000d 00000000f5000000 0000000000000000
head: 00fff00000000002 ffffea0001626f01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000004
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5819, tgid 5819 (syz-executor), ts 63017728292, free_ts 14412109844
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x153/0x170 mm/page_alloc.c:1889
prep_new_page mm/page_alloc.c:1897 [inline]
get_page_from_freelist+0x111d/0x3140 mm/page_alloc.c:3962
__alloc_frozen_pages_noprof+0x27c/0x2ba0 mm/page_alloc.c:5250
alloc_slab_page mm/slub.c:3292 [inline]
allocate_slab mm/slub.c:3481 [inline]
new_slab+0xa6/0x6b0 mm/slub.c:3539
refill_objects+0x26b/0x400 mm/slub.c:7175
refill_sheaf mm/slub.c:2812 [inline]
__pcs_replace_empty_main+0x1ab/0x660 mm/slub.c:4615
alloc_from_pcs mm/slub.c:4717 [inline]
slab_alloc_node mm/slub.c:4851 [inline]
__kmalloc_cache_noprof+0x493/0x6f0 mm/slub.c:5375
kmalloc_noprof include/linux/slab.h:950 [inline]
kzalloc_noprof include/linux/slab.h:1188 [inline]
mca_alloc net/ipv6/mcast.c:871 [inline]
__ipv6_dev_mc_inc+0x2f1/0xbc0 net/ipv6/mcast.c:961
ipv6_add_dev+0xb78/0x1520 net/ipv6/addrconf.c:471
addrconf_notify+0x563/0x19c0 net/ipv6/addrconf.c:3654
notifier_call_chain+0x99/0x420 kernel/notifier.c:85
call_netdevice_notifiers_info+0xbe/0x110 net/core/dev.c:2249
call_netdevice_notifiers_extack net/core/dev.c:2287 [inline]
call_netdevice_notifiers net/core/dev.c:2301 [inline]
register_netdevice+0x16e6/0x2210 net/core/dev.c:11474
veth_newlink+0x44a/0xa00 drivers/net/veth.c:1889
rtnl_newlink_create net/core/rtnetlink.c:3862 [inline]
__rtnl_newlink net/core/rtnetlink.c:3979 [inline]
rtnl_newlink+0x1494/0x2380 net/core/rtnetlink.c:4094
rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6980
page last free pid 1 tgid 1 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1433 [inline]
__free_frozen_pages+0x7e1/0x10d0 mm/page_alloc.c:2978
__free_pages mm/page_alloc.c:5369 [inline]
free_contig_range+0xde/0x1d0 mm/page_alloc.c:7374
debug_vm_pgtable_free_huge_page mm/debug_vm_pgtable.c:980 [inline]
destroy_args+0xa8/0x7a0 mm/debug_vm_pgtable.c:993
debug_vm_pgtable+0x1b66/0x34c0 mm/debug_vm_pgtable.c:1368
do_one_initcall+0x11d/0x760 init/main.c:1382
do_initcall_level init/main.c:1444 [inline]
do_initcalls init/main.c:1460 [inline]
do_basic_setup init/main.c:1479 [inline]
kernel_init_freeable+0x6e5/0x7a0 init/main.c:1692
kernel_init+0x1f/0x1e0 init/main.c:1582
ret_from_fork+0x754/0xd80 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
ffff8880589bdb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880589bdb80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880589bdc00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880589bdc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880589bdd00: 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 80 b8 43 f6 call 0xf643b89f
1f: e8 3b ce 7e f6 call 0xf67ece5f
24: fb sti
25: bf 01 00 00 00 mov $0x1,%edi
* 2a: e8 e0 96 ff ff call 0xffff970f <-- 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: 9e sahf
3e: 56 push %rsi
3f: 43 rex.XB

---
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