==================================================================
BUG: KASAN: slab-use-after-free in ax25_heartbeat_expiry+0x115/0x140 net/ax25/ax25_timer.c:127
Read of size 4 at addr ffff888077578260 by task syz-executor/8694

CPU: 1 UID: 0 PID: 8694 Comm: syz-executor Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 ax25_heartbeat_expiry+0x115/0x140 net/ax25/ax25_timer.c:127
 call_timer_fn+0x192/0x5a0 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers kernel/time/timer.c:2373 [inline]
 __run_timer_base+0x652/0x8b0 kernel/time/timer.c:2385
 run_timer_base kernel/time/timer.c:2394 [inline]
 run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2404
 handle_softirqs+0x22a/0x7c0 kernel/softirq.c:626
 __do_softirq kernel/softirq.c:660 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x5f/0x150 kernel/softirq.c:727
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:743
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 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:__sanitizer_cov_trace_pc+0x0/0x70 kernel/kcov.c:210
Code: 89 fb e8 23 00 00 00 48 8b 3d 94 06 66 0c 48 89 de 5b e9 b3 c7 5d 00 cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <f3> 0f 1e fa 48 8b 04 24 65 48 8b 0d b8 b6 76 11 65 8b 15 d9 b6 76
RSP: 0018:ffffc90002e96860 EFLAGS: 00000246
RAX: ffffffff826bbbd8 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff888025f51e40 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff88807ef72008 R08: 0000000000400dc0 R09: 00000000ffffffff
R10: 0000000000000016 R11: ffffffff81b05a80 R12: 0000000000000380
R13: dffffc0000000000 R14: 0000000000000011 R15: ffff88807ef72388
 __register_sysctl_table+0x9d7/0x1340 fs/proc/proc_sysctl.c:1386
 neigh_sysctl_register+0x9b1/0xa90 net/core/neighbour.c:3886
 devinet_sysctl_register+0xad/0x200 net/ipv4/devinet.c:2714
 inetdev_init+0x2b1/0x4f0 net/ipv4/devinet.c:291
 inetdev_event+0x30d/0x1610 net/ipv4/devinet.c:1590
 notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2281 [inline]
 call_netdevice_notifiers net/core/dev.c:2295 [inline]
 register_netdevice+0x190b/0x1ed0 net/core/dev.c:11461
 veth_newlink+0x67b/0xb70 drivers/net/veth.c:1889
 rtnl_newlink_create+0x329/0xb70 net/core/rtnetlink.c:3840
 __rtnl_newlink net/core/rtnetlink.c:3957 [inline]
 rtnl_newlink+0x1666/0x1be0 net/core/rtnetlink.c:4072
 rtnetlink_rcv_msg+0x7d5/0xbe0 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2550
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x80f/0x9b0 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec+0x18f/0x1d0 net/socket.c:737
 __sock_sendmsg net/socket.c:752 [inline]
 __sys_sendto+0x3ff/0x590 net/socket.c:2221
 __do_sys_sendto net/socket.c:2228 [inline]
 __se_sys_sendto net/socket.c:2224 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2224
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbb6135b78e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007ffc28031bf8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 000055558d4ec500 RCX: 00007fbb6135b78e
RDX: 000000000000003c RSI: 00007fbb62144670 RDI: 0000000000000003
RBP: 0000000000000001 R08: 00007ffc28031c74 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 0000000000000000 R14: 00007fbb62144670 R15: 0000000000000000
 </TASK>

Allocated by task 6899:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5290
 kmalloc_noprof include/linux/slab.h:962 [inline]
 kzalloc_noprof include/linux/slab.h:1204 [inline]
 ax25_dev_device_up+0x54/0x600 net/ax25/ax25_dev.c:57
 ax25_device_event+0x127/0x8a0 net/ax25/af_ax25.c:143
 notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2281 [inline]
 call_netdevice_notifiers net/core/dev.c:2295 [inline]
 __dev_notify_flags+0x1a9/0x310 net/core/dev.c:9788
 netif_change_flags+0xe8/0x1a0 net/core/dev.c:9817
 dev_change_flags+0x130/0x260 net/core/dev_api.c:68
 dev_ioctl+0x7b4/0x1150 net/core/dev_ioctl.c:814
 sock_do_ioctl+0x23e/0x320 net/socket.c:1283
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1390
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5829:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2667 [inline]
 __rcu_free_sheaf_prepare+0x129/0x290 mm/slub.c:2897
 rcu_free_sheaf+0x31/0x200 mm/slub.c:5721
 rcu_do_batch kernel/rcu/tree.c:2617 [inline]
 rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
 handle_softirqs+0x22a/0x7c0 kernel/softirq.c:626
 __do_softirq kernel/softirq.c:660 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x5f/0x150 kernel/softirq.c:727
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:743
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 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 ffff888077578200
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 96 bytes inside of
 freed 256-byte region [ffff888077578200, ffff888077578300)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x77578
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813ff26b40 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813ff26b40 dead000000000100 dead000000000122
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000001 ffffea0001dd5e01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5971, tgid 5970 (syz.0.15), ts 97598846236, free_ts 97571857022
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1883
 prep_new_page mm/page_alloc.c:1891 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3956
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5244
 alloc_slab_page mm/slub.c:3235 [inline]
 allocate_slab+0x7b/0x660 mm/slub.c:3408
 new_slab mm/slub.c:3466 [inline]
 refill_objects+0x33a/0x3d0 mm/slub.c:7077
 refill_sheaf mm/slub.c:2784 [inline]
 __pcs_replace_empty_main+0x2b9/0x620 mm/slub.c:4529
 alloc_from_pcs mm/slub.c:4632 [inline]
 slab_alloc_node mm/slub.c:4766 [inline]
 __kmalloc_cache_noprof+0x392/0x660 mm/slub.c:5285
 kmalloc_noprof include/linux/slab.h:962 [inline]
 alloc_name mm/memfd.c:437 [inline]
 __do_sys_memfd_create mm/memfd.c:518 [inline]
 __se_sys_memfd_create+0x227/0x420 mm/memfd.c:506
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5971 tgid 5970 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1432 [inline]
 __free_frozen_pages+0xc01/0xd80 mm/page_alloc.c:2972
 __slab_free+0x263/0x2b0 mm/slub.c:5483
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4452 [inline]
 slab_alloc_node mm/slub.c:4781 [inline]
 kmem_cache_alloc_node_noprof+0x384/0x690 mm/slub.c:4833
 __alloc_skb+0x1d0/0x7d0 net/core/skbuff.c:701
 alloc_skb include/linux/skbuff.h:1383 [inline]
 nlmsg_new include/net/netlink.h:1055 [inline]
 rtmsg_ifinfo_build_skb+0x84/0x260 net/core/rtnetlink.c:4407
 rtmsg_ifinfo_event net/core/rtnetlink.c:4449 [inline]
 rtmsg_ifinfo+0x8c/0x1a0 net/core/rtnetlink.c:4458
 register_netdevice+0x1af4/0x1ed0 net/core/dev.c:11475
 tun_set_iff+0x844/0xf00 drivers/net/tun.c:2807
 __tun_chr_ioctl+0x7c8/0x1e30 drivers/net/tun.c:3088
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888077578100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888077578180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888077578200: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff888077578280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888077578300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
----------------
Code disassembly (best guess):
   0:	89 fb                	mov    %edi,%ebx
   2:	e8 23 00 00 00       	call   0x2a
   7:	48 8b 3d 94 06 66 0c 	mov    0xc660694(%rip),%rdi        # 0xc6606a2
   e:	48 89 de             	mov    %rbx,%rsi
  11:	5b                   	pop    %rbx
  12:	e9 b3 c7 5d 00       	jmp    0x5dc7ca
  17:	cc                   	int3
  18:	cc                   	int3
  19:	cc                   	int3
  1a:	90                   	nop
  1b:	90                   	nop
  1c:	90                   	nop
  1d:	90                   	nop
  1e:	90                   	nop
  1f:	90                   	nop
  20:	90                   	nop
  21:	90                   	nop
  22:	90                   	nop
  23:	90                   	nop
  24:	90                   	nop
  25:	90                   	nop
  26:	90                   	nop
  27:	90                   	nop
  28:	90                   	nop
  29:	90                   	nop
* 2a:	f3 0f 1e fa          	endbr64 <-- trapping instruction
  2e:	48 8b 04 24          	mov    (%rsp),%rax
  32:	65 48 8b 0d b8 b6 76 	mov    %gs:0x1176b6b8(%rip),%rcx        # 0x1176b6f2
  39:	11
  3a:	65                   	gs
  3b:	8b                   	.byte 0x8b
  3c:	15                   	.byte 0x15
  3d:	d9                   	.byte 0xd9
  3e:	b6 76                	mov    $0x76,%dh