==================================================================
BUG: KASAN: use-after-free in ax25_heartbeat_expiry+0x10c/0x130 net/ax25/ax25_timer.c:127
Read of size 4 at addr ffff88807f92ec60 by task ksoftirqd/1/21

CPU: 1 PID: 21 Comm: ksoftirqd/1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:420
 kasan_report+0x10b/0x140 mm/kasan/report.c:524
 ax25_heartbeat_expiry+0x10c/0x130 net/ax25/ax25_timer.c:127
 call_timer_fn+0x1ac/0x670 kernel/time/timer.c:1701
 expire_timers kernel/time/timer.c:1752 [inline]
 __run_timers+0x53e/0x800 kernel/time/timer.c:2023
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:2036
 handle_softirqs+0x2a1/0x930 kernel/softirq.c:596
 run_ksoftirqd+0xa4/0x100 kernel/softirq.c:968
 smpboot_thread_fn+0x64a/0xa40 kernel/smpboot.c:164
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>

Allocated by task 6818:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0x8e/0xa0 mm/kasan/common.c:384
 kmalloc include/linux/slab.h:563 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 ax25_dev_device_up+0x50/0x5f0 net/ax25/ax25_dev.c:57
 ax25_device_event+0x117/0x600 net/ax25/af_ax25.c:143
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:455
 call_netdevice_notifiers_extack net/core/dev.c:2052 [inline]
 call_netdevice_notifiers net/core/dev.c:2066 [inline]
 __dev_notify_flags+0x194/0x300 net/core/dev.c:8689
 dev_change_flags+0xe3/0x1a0 net/core/dev.c:8727
 dev_ifsioc+0x130/0xd40 net/core/dev_ioctl.c:326
 dev_ioctl+0x55e/0xe80 net/core/dev_ioctl.c:572
 sock_do_ioctl+0x245/0x320 net/socket.c:1215
 sock_ioctl+0x4d2/0x710 net/socket.c:1320
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 6620:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x2d/0x50 mm/kasan/generic.c:516
 ____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:237
 kasan_slab_free include/linux/kasan.h:177 [inline]
 slab_free_hook mm/slub.c:1729 [inline]
 slab_free_freelist_hook+0x131/0x1a0 mm/slub.c:1755
 slab_free mm/slub.c:3687 [inline]
 kmem_cache_free_bulk+0x348/0x460 mm/slub.c:3805
 kfree_bulk include/linux/slab.h:475 [inline]
 kfree_rcu_work+0x33f/0x890 kernel/rcu/tree.c:3091
 process_one_work+0x8a2/0x1160 kernel/workqueue.c:2292
 worker_thread+0xaa2/0x1270 kernel/workqueue.c:2439
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xb2/0xc0 mm/kasan/generic.c:486
 kvfree_call_rcu+0x103/0x870 kernel/rcu/tree.c:3405
 ax25_device_event+0x555/0x600 net/ax25/af_ax25.c:148
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:455
 call_netdevice_notifiers_extack net/core/dev.c:2052 [inline]
 call_netdevice_notifiers net/core/dev.c:2066 [inline]
 __dev_notify_flags+0x158/0x300 net/core/dev.c:8691
 dev_change_flags+0xe3/0x1a0 net/core/dev.c:8727
 dev_ifsioc+0x130/0xd40 net/core/dev_ioctl.c:326
 dev_ioctl+0x55e/0xe80 net/core/dev_ioctl.c:572
 sock_do_ioctl+0x245/0x320 net/socket.c:1215
 sock_ioctl+0x4d2/0x710 net/socket.c:1320
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Second to last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xb2/0xc0 mm/kasan/generic.c:486
 kvfree_call_rcu+0x103/0x870 kernel/rcu/tree.c:3405
 drop_sysctl_table+0x359/0x4e0 fs/proc/proc_sysctl.c:1731
 drop_sysctl_table+0x348/0x4e0 fs/proc/proc_sysctl.c:1734
 unregister_sysctl_table+0x85/0x130 fs/proc/proc_sysctl.c:1769
 __addrconf_sysctl_unregister net/ipv6/addrconf.c:7179 [inline]
 addrconf_sysctl_unregister net/ipv6/addrconf.c:7207 [inline]
 addrconf_ifdown+0x16c6/0x1a50 net/ipv6/addrconf.c:3951
 addrconf_notify+0x405/0xf40 net/ipv6/addrconf.c:-1
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:455
 call_netdevice_notifiers_extack net/core/dev.c:2052 [inline]
 call_netdevice_notifiers net/core/dev.c:2066 [inline]
 unregister_netdevice_many+0x1086/0x1930 net/core/dev.c:11003
 default_device_exit_batch+0x9e6/0xa80 net/core/dev.c:11516
 ops_exit_list net/core/net_namespace.c:177 [inline]
 cleanup_net+0x791/0xba0 net/core/net_namespace.c:640
 process_one_work+0x8a2/0x1160 kernel/workqueue.c:2292
 worker_thread+0xaa2/0x1270 kernel/workqueue.c:2439
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

The buggy address belongs to the object at ffff88807f92ec00
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 96 bytes inside of
 256-byte region [ffff88807f92ec00, ffff88807f92ed00)

The buggy address belongs to the physical page:
page:ffffea0001fe4b80 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7f92e
head:ffffea0001fe4b80 order:1 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 ffffea00008ea300 dead000000000004 ffff888017441b40
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
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 4278, tgid 4278 (syz-executor), ts 78752355533, free_ts 78533941682
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2559
 prep_new_page mm/page_alloc.c:2566 [inline]
 get_page_from_freelist+0x1a1e/0x1ab0 mm/page_alloc.c:4357
 __alloc_pages+0x1ec/0x4f0 mm/page_alloc.c:5643
 alloc_slab_page+0x5d/0x160 mm/slub.c:1799
 allocate_slab mm/slub.c:1944 [inline]
 new_slab+0x87/0x2c0 mm/slub.c:1997
 ___slab_alloc+0xbc6/0x1240 mm/slub.c:3154
 __slab_alloc mm/slub.c:3240 [inline]
 slab_alloc_node mm/slub.c:3325 [inline]
 __kmem_cache_alloc_node+0x1a0/0x260 mm/slub.c:3398
 __do_kmalloc_node mm/slab_common.c:935 [inline]
 __kmalloc+0xa0/0x240 mm/slab_common.c:949
 kmalloc include/linux/slab.h:568 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 new_dir fs/proc/proc_sysctl.c:973 [inline]
 get_subdir fs/proc/proc_sysctl.c:1017 [inline]
 __register_sysctl_table+0x96c/0xe70 fs/proc/proc_sysctl.c:1379
 neigh_sysctl_register+0x9a2/0xa80 net/core/neighbour.c:3858
 addrconf_sysctl_register+0xac/0x1b0 net/ipv6/addrconf.c:7193
 ipv6_add_dev+0xbe0/0x1120 net/ipv6/addrconf.c:451
 addrconf_notify+0x634/0xf40 net/ipv6/addrconf.c:3595
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:455
 call_netdevice_notifiers_extack net/core/dev.c:2052 [inline]
 call_netdevice_notifiers net/core/dev.c:2066 [inline]
 register_netdevice+0x163f/0x1b00 net/core/dev.c:10250
 veth_newlink+0x60f/0xc80 drivers/net/veth.c:1725
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1486 [inline]
 free_pcp_prepare mm/page_alloc.c:1536 [inline]
 free_unref_page_prepare+0x8b4/0x9a0 mm/page_alloc.c:3413
 free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3508
 free_slab mm/slub.c:2036 [inline]
 discard_slab mm/slub.c:2042 [inline]
 __unfreeze_partials+0x1a5/0x200 mm/slub.c:2591
 put_cpu_partial+0x17c/0x250 mm/slub.c:2667
 qlink_free mm/kasan/quarantine.c:168 [inline]
 qlist_free_all+0x76/0xe0 mm/kasan/quarantine.c:187
 kasan_quarantine_reduce+0x144/0x160 mm/kasan/quarantine.c:294
 __kasan_slab_alloc+0x1e/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:201 [inline]
 slab_post_alloc_hook+0x4b/0x480 mm/slab.h:737
 slab_alloc_node mm/slub.c:3359 [inline]
 __kmem_cache_alloc_node+0x140/0x260 mm/slub.c:3398
 kmalloc_trace+0x26/0xe0 mm/slab_common.c:1026
 kmalloc include/linux/slab.h:563 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 kset_create lib/kobject.c:950 [inline]
 kset_create_and_add+0x56/0x160 lib/kobject.c:993
 register_queue_kobjects net/core/net-sysfs.c:1764 [inline]
 netdev_register_kobject+0x1ae/0x320 net/core/net-sysfs.c:2017
 register_netdevice+0x12dc/0x1b00 net/core/dev.c:10217
 veth_newlink+0x60f/0xc80 drivers/net/veth.c:1725
 rtnl_newlink_create net/core/rtnetlink.c:3422 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3642 [inline]
 rtnl_newlink+0x1542/0x2080 net/core/rtnetlink.c:3655
 rtnetlink_rcv_msg+0x87c/0xfc0 net/core/rtnetlink.c:6150

Memory state around the buggy address:
 ffff88807f92eb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88807f92eb80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88807f92ec00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff88807f92ec80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807f92ed00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================