KASAN: use-after-free Write in l2tp_session_delete

Status: auto-obsoleted due to no activity on 2025/01/19 22:14
Reported-by: syzbot+0e73375855425d155f17@syzkaller.appspotmail.com
First crash: 668d, last: 644d
▶ ▼ Similar bugs (14)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-10 KASAN: use-after-free Write in l2tp_session_delete (2) 22 3 443d 544d 0/2 auto-obsoleted due to no activity on 2025/08/08 12:20
android-5-10 KASAN: use-after-free Write in l2tp_session_delete (3) 22 5 200d 316d 0/2 auto-obsoleted due to no activity on 2026/04/09 06:46
android-6-1 KASAN: use-after-free Write in l2tp_session_delete (2) 22 1 157d 157d 0/2 auto-obsoleted due to no activity on 2026/05/22 02:12
android-6-1 KASAN: use-after-free Write in l2tp_session_delete (3) 22 4 6h13m 34d 0/2 premoderation: reported on 2026/06/24 03:10
linux-6.1 KASAN: use-after-free Write in l2tp_session_delete (2) 22 1 189d 189d 0/3 auto-obsoleted due to no activity on 2026/04/29 20:48
linux-6.1 KASAN: use-after-free Write in l2tp_session_delete 22 2 676d 698d 0/3 auto-obsoleted due to no activity on 2024/12/29 03:40
android-5-15 KASAN: use-after-free Write in l2tp_session_delete 22 2 761d 774d 0/2 auto-obsoleted due to no activity on 2024/09/25 05:09
android-5-15 KASAN: use-after-free Write in l2tp_session_delete (2) origin:downstream 22 C error 29 5d22h 502d 0/2 upstream: reported C repro on 2025/03/13 02:24
linux-5.15 KASAN: use-after-free Write in l2tp_session_delete 22 2 1093d 1181d 0/3 auto-obsoleted due to no activity on 2023/11/08 00:22
linux-5.15 KASAN: use-after-free Write in l2tp_session_delete (2) 22 2 588d 676d 0/3 auto-obsoleted due to no activity on 2025/03/26 11:58
android-5-10 KASAN: use-after-free Write in l2tp_session_delete (4) 22 C 7 20d 30d 0/2 upstream: reported C repro on 2026/06/28 05:46
android-6-1 KASAN: use-after-free Write in l2tp_session_delete origin:downstream 22 syz error 20 253d 657d 0/2 auto-obsoleted due to no activity on 2026/02/14 16:29
linux-5.15 KASAN: use-after-free Write in l2tp_session_delete (3) 22 1 368d 368d 0/3 auto-obsoleted due to no activity on 2025/11/02 00:17
upstream KASAN: slab-use-after-free Write in l2tp_session_delete net 22 C done 1286 743d 762d 27/29 fixed on 2024/08/14 03:44

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: use-after-free in test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:70 [inline]
BUG: KASAN: use-after-free in l2tp_session_delete+0x24/0x4e0 net/l2tp/l2tp_core.c:1563
Write of size 8 at addr ffff88810f0e7c08 by task kworker/u4:7/7629

CPU: 0 PID: 7629 Comm: kworker/u4:7 Not tainted 5.10.226-syzkaller-00709-ge5e5644ea27f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack_lvl+0x1e2/0x24b lib/dump_stack.c:118
 print_address_description+0x81/0x3b0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0x179/0x1c0 mm/kasan/report.c:452
 kasan_check_range+0x293/0x2a0 mm/kasan/generic.c:189
 __kasan_check_write+0x14/0x20 mm/kasan/shadow.c:37
 instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
 test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:70 [inline]
 l2tp_session_delete+0x24/0x4e0 net/l2tp/l2tp_core.c:1563
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1218 [inline]
 l2tp_tunnel_del_work+0x19d/0x380 net/l2tp/l2tp_core.c:1258
 process_one_work+0x6dc/0xbd0 kernel/workqueue.c:2301
 worker_thread+0xaea/0x1510 kernel/workqueue.c:2447
 kthread+0x34b/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

Allocated by task 13021:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:430 [inline]
 ____kasan_kmalloc+0xdb/0x110 mm/kasan/common.c:509
 __kasan_kmalloc+0x9/0x10 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 __kmalloc+0x1aa/0x330 mm/slub.c:4033
 kmalloc include/linux/slab.h:557 [inline]
 kzalloc include/linux/slab.h:664 [inline]
 l2tp_session_create+0x38/0xb60 net/l2tp/l2tp_core.c:1599
 pppol2tp_connect+0xc5d/0x1690 net/l2tp/l2tp_ppp.c:782
 __sys_connect_file net/socket.c:1866 [inline]
 __sys_connect+0x388/0x410 net/socket.c:1883
 __do_sys_connect net/socket.c:1893 [inline]
 __se_sys_connect net/socket.c:1890 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:1890
 do_syscall_64+0x34/0x70
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Freed by task 19:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x121/0x160 mm/kasan/common.c:362
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370
 kasan_slab_free include/linux/kasan.h:220 [inline]
 slab_free_hook mm/slub.c:1595 [inline]
 slab_free_freelist_hook+0xc0/0x190 mm/slub.c:1621
 slab_free mm/slub.c:3203 [inline]
 kfree+0xc3/0x270 mm/slub.c:4191
 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
 l2tp_session_dec_refcount+0xac/0x1b0 net/l2tp/l2tp_core.c:205
 pppol2tp_session_destruct+0xaf/0xf0 net/l2tp/l2tp_ppp.c:419
 __sk_destruct+0x59/0x620 net/core/sock.c:1813
 sk_destruct net/core/sock.c:1858 [inline]
 __sk_free+0x36c/0x470 net/core/sock.c:1869
 sk_free+0x51/0x80 net/core/sock.c:1880
 sock_put include/net/sock.h:1850 [inline]
 pppol2tp_put_sk+0x77/0xb0 net/l2tp/l2tp_ppp.c:402
 rcu_do_batch+0x597/0xc40 kernel/rcu/tree.c:2494
 rcu_core+0x5ad/0xe40 kernel/rcu/tree.c:2735
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748
 __do_softirq+0x268/0x5bb kernel/softirq.c:309

Last potentially related work creation:
 kasan_save_stack+0x3b/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd3/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 __call_rcu kernel/rcu/tree.c:2976 [inline]
 call_rcu+0x135/0x11f0 kernel/rcu/tree.c:3050
 pppol2tp_release+0x20f/0x2d0 net/l2tp/l2tp_ppp.c:458
 __sock_release net/socket.c:597 [inline]
 sock_close+0xdf/0x270 net/socket.c:1286
 __fput+0x33d/0x7b0 fs/file_table.c:281
 ____fput+0x15/0x20 fs/file_table.c:314
 task_work_run+0x129/0x190 kernel/task_work.c:189
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop+0xbf/0xd0 kernel/entry/common.c:172
 exit_to_user_mode_prepare kernel/entry/common.c:199 [inline]
 syscall_exit_to_user_mode+0xa2/0x1a0 kernel/entry/common.c:274
 do_syscall_64+0x40/0x70 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Second to last potentially related work creation:
 kasan_save_stack+0x3b/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd3/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 kvfree_call_rcu+0x136/0x650 kernel/rcu/tree.c:3535
 drop_sysctl_table+0x311/0x450 fs/proc/proc_sysctl.c:1680
 drop_sysctl_table+0x323/0x450 fs/proc/proc_sysctl.c:1683
 unregister_sysctl_table+0x76/0x120 fs/proc/proc_sysctl.c:1718
 unregister_net_sysctl_table+0x15/0x20 net/sysctl_net.c:127
 neigh_sysctl_unregister+0x78/0x90 net/core/neighbour.c:3732
 devinet_sysctl_unregister net/ipv4/devinet.c:2637 [inline]
 inetdev_destroy net/ipv4/devinet.c:324 [inline]
 inetdev_event+0x7c1/0x1040 net/ipv4/devinet.c:1599
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0x8c/0xf0 kernel/notifier.c:410
 call_netdevice_notifiers_info net/core/dev.c:2054 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2066 [inline]
 call_netdevice_notifiers net/core/dev.c:2080 [inline]
 unregister_netdevice_many+0xde7/0x17d0 net/core/dev.c:10747
 default_device_exit_batch+0x38a/0x3f0 net/core/dev.c:11267
 ops_exit_list net/core/net_namespace.c:190 [inline]
 cleanup_net+0x6e9/0xcb0 net/core/net_namespace.c:609
 process_one_work+0x6dc/0xbd0 kernel/workqueue.c:2301
 worker_thread+0xaea/0x1510 kernel/workqueue.c:2447
 kthread+0x34b/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

The buggy address belongs to the object at ffff88810f0e7c00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 8 bytes inside of
 512-byte region [ffff88810f0e7c00, ffff88810f0e7e00)
The buggy address belongs to the page:
page:ffffea00043c3900 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10f0e4
head:ffffea00043c3900 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100043080
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
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 95, ts 3965303348, free_ts 0
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x166/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x2d8c/0x2f30 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x435/0xaf0 mm/page_alloc.c:5348
 allocate_slab mm/slub.c:1808 [inline]
 new_slab+0x80/0x400 mm/slub.c:1869
 new_slab_objects mm/slub.c:2627 [inline]
 ___slab_alloc+0x302/0x4b0 mm/slub.c:2791
 __slab_alloc+0x63/0xa0 mm/slub.c:2831
 slab_alloc_node mm/slub.c:2913 [inline]
 slab_alloc mm/slub.c:2955 [inline]
 __kmalloc_track_caller+0x1f8/0x320 mm/slub.c:4536
 __kmalloc_reserve net/core/skbuff.c:144 [inline]
 __alloc_skb+0xbc/0x510 net/core/skbuff.c:212
 alloc_skb include/linux/skbuff.h:1126 [inline]
 alloc_uevent_skb+0x80/0x230 lib/kobject_uevent.c:290
 uevent_net_broadcast_untagged lib/kobject_uevent.c:326 [inline]
 kobject_uevent_net_broadcast+0x311/0x590 lib/kobject_uevent.c:409
 kobject_uevent_env+0x525/0x700 lib/kobject_uevent.c:608
 kobject_synth_uevent+0x4eb/0xae0 lib/kobject_uevent.c:208
 store_uevent+0x16/0x30 kernel/module.c:1233
 module_attr_store+0x5c/0x80 kernel/params.c:921
 sysfs_kf_write+0x123/0x140 fs/sysfs/file.c:139
 kernfs_fop_write_iter+0x2c4/0x410 fs/kernfs/file.c:296
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810f0e7b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88810f0e7b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88810f0e7c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88810f0e7c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810f0e7d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2024/10/21 22:10 android13-5.10-lts e5e5644ea27f f1e4447c .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Write in l2tp_session_delete
2024/09/28 01:23 android13-5.10-lts 8d23314f588a 440b26ec .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Write in l2tp_session_delete
* Struck through repros no longer work on HEAD.