KASAN: use-after-free Read in l2tp_tunnel_del_work

Status: premoderation: reported on 2026/06/23 09:58
Reported-by: syzbot+debdd4ed13bf7673952e@syzkaller.appspotmail.com
First crash: 71d, last: 40m
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work 19 syz, C 68 10d 18d 0/2 upstream: reported C repro on 2026/08/15 11:07
android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work 19 87 17h54m 67d 0/2 premoderation: reported on 2026/06/27 08:43
upstream KASAN: use-after-free Write in l2tp_tunnel_del_work (2) net 22 syz unreliable done 2 1300d 1366d 0/29 auto-obsoleted due to no activity on 2023/06/10 16:21
upstream KASAN: use-after-free Write in l2tp_tunnel_del_work net 22 1 1735d 1730d 0/29 auto-closed as invalid on 2022/04/01 19:17
upstream KASAN: slab-use-after-free Read in l2tp_tunnel_del_work net 19 syz, C done 99 785d 799d 27/29 fixed on 2024/08/14 03:44

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in hlist_unhashed include/linux/list.h:808 [inline]
BUG: KASAN: use-after-free in hlist_del_init include/linux/list.h:865 [inline]
BUG: KASAN: use-after-free in l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1232 [inline]
BUG: KASAN: use-after-free in l2tp_tunnel_del_work+0xcd/0x3d0 net/l2tp/l2tp_core.c:1273
Read of size 8 at addr ffff88811b425880 by task kworker/u4:0/7

CPU: 1 PID: 7 Comm: kworker/u4:0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0x100/0x140 mm/kasan/report.c:452
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309
 hlist_unhashed include/linux/list.h:808 [inline]
 hlist_del_init include/linux/list.h:865 [inline]
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1232 [inline]
 l2tp_tunnel_del_work+0xcd/0x3d0 net/l2tp/l2tp_core.c:1273
 process_one_work+0x6fd/0xbc0 kernel/workqueue.c:2301
 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447
 kthread+0x324/0x3b0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

Allocated by task 740:
 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 mm/kasan/common.c:509 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 __kmalloc+0x19f/0x330 mm/slub.c:4038
 kmalloc include/linux/slab.h:560 [inline]
 kzalloc include/linux/slab.h:667 [inline]
 l2tp_session_create+0x39/0xb60 net/l2tp/l2tp_core.c:1616
 pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:772
 __sys_connect_file net/socket.c:1867 [inline]
 __sys_connect+0x3ce/0x450 net/socket.c:1884
 __do_sys_connect net/socket.c:1894 [inline]
 __se_sys_connect net/socket.c:1891 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:1891
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Freed by task 754:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 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:1600 [inline]
 slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626
 slab_free mm/slub.c:3208 [inline]
 kfree+0xc0/0x270 mm/slub.c:4196
 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
 l2tp_session_put+0xb2/0x1a0 net/l2tp/l2tp_core.c:193
 pppol2tp_ioctl+0x748/0x960 net/l2tp/l2tp_ppp.c:-1
 pppox_ioctl+0x1e4/0x320 drivers/net/ppp/pppox.c:93
 sock_do_ioctl+0xda/0x380 net/socket.c:1068
 sock_ioctl+0x472/0x740 net/socket.c:1208
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0x121/0x1a0 fs/ioctl.c:739
 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:739
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

The buggy address belongs to the object at ffff88811b425800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
 512-byte region [ffff88811b425800, ffff88811b425a00)
The buggy address belongs to the page:
page:ffffea00046d0900 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11b424
head:ffffea00046d0900 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 166, ts 6759385413, 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+0x176/0x190 mm/page_alloc.c:2462
 get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1813 [inline]
 new_slab+0x84/0x3f0 mm/slub.c:1874
 new_slab_objects mm/slub.c:2632 [inline]
 ___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796
 __slab_alloc+0x63/0xa0 mm/slub.c:2836
 slab_alloc_node mm/slub.c:2918 [inline]
 slab_alloc mm/slub.c:2960 [inline]
 kmem_cache_alloc_trace+0x1a8/0x2e0 mm/slub.c:2977
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:667 [inline]
 alloc_bprm+0x59/0x630 fs/exec.c:1503
 do_execveat_common+0x1b1/0xab0 fs/exec.c:1905
 do_execve fs/exec.c:2024 [inline]
 __do_sys_execve fs/exec.c:2100 [inline]
 __se_sys_execve fs/exec.c:2095 [inline]
 __x64_sys_execve+0x92/0xb0 fs/exec.c:2095
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88811b425780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88811b425800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88811b425880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff88811b425900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88811b425980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 7 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 1 PID: 7 Comm: kworker/u4:0 Tainted: G    B             syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: l2tp l2tp_tunnel_del_work
RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Code: 04 01 48 c7 c7 40 51 40 85 e8 ec 4b 3b 02 0f 0b eb c3 e8 c3 92 26 ff c6 05 71 77 82 04 01 48 c7 c7 a0 51 40 85 e8 d0 4b 3b 02 <0f> 0b eb a7 e8 a7 92 26 ff c6 05 52 77 82 04 01 48 c7 c7 c0 50 40
RSP: 0018:ffffc90000077c58 EFLAGS: 00010246
RAX: 4cb30f7e83ba1200 RBX: 0000000000000003 RCX: ffff88810024a780
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90000077c68 R08: ffff8881f7052fbf R09: 1ffff1103ee0a5f7
R10: dffffc0000000000 R11: ffffed103ee0a5f8 R12: ffff88811b427c20
R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200001000000 CR3: 000000010d502000 CR4: 00000000003526b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __refcount_sub_and_test include/linux/refcount.h:283 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 l2tp_session_put+0xcb/0x1a0 net/l2tp/l2tp_core.c:192
 l2tp_session_delete+0x3a9/0x4a0 net/l2tp/l2tp_core.c:1589
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1235 [inline]
 l2tp_tunnel_del_work+0x180/0x3d0 net/l2tp/l2tp_core.c:1273
 process_one_work+0x6fd/0xbc0 kernel/workqueue.c:2301
 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447
 kthread+0x324/0x3b0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298
---[ end trace 764a7b2f0d942e83 ]---

Crashes (200):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/02 21:15 android13-5.10-lts 4185c27befd4 85995287 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/02 17:00 android13-5.10-lts 4185c27befd4 85995287 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/02 12:58 android13-5.10-lts 4185c27befd4 85995287 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/02 11:41 android13-5.10-lts 4185c27befd4 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/02 07:24 android13-5.10-lts 4185c27befd4 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/02 00:46 android13-5.10-lts 4185c27befd4 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 23:15 android13-5.10-lts 4f08b4b867e1 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 21:20 android13-5.10-lts 4f08b4b867e1 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 19:51 android13-5.10-lts 4f08b4b867e1 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 16:39 android13-5.10-lts 4f08b4b867e1 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 12:35 android13-5.10-lts 4f08b4b867e1 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 11:17 android13-5.10-lts 4f08b4b867e1 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 09:40 android13-5.10-lts 4f08b4b867e1 316d9396 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 08:26 android13-5.10-lts 174d3ccb72b8 316d9396 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 06:06 android13-5.10-lts 174d3ccb72b8 316d9396 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 04:55 android13-5.10-lts 174d3ccb72b8 316d9396 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 00:53 android13-5.10-lts 174d3ccb72b8 316d9396 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/31 18:28 android13-5.10-lts 174d3ccb72b8 316d9396 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/31 15:29 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/31 09:44 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/31 07:29 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/30 17:24 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/30 15:19 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/30 07:34 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/30 03:08 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/30 01:31 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/29 20:40 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/29 06:41 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/29 04:25 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/28 04:50 android13-5.10-lts 174d3ccb72b8 69a01293 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/28 02:27 android13-5.10-lts 174d3ccb72b8 69a01293 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/27 06:13 android13-5.10-lts 174d3ccb72b8 a2b77b9e .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/26 17:47 android13-5.10-lts 174d3ccb72b8 a2b77b9e .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/25 23:18 android13-5.10-lts f01343e230a3 a9a1fc32 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/24 15:06 android13-5.10-lts 7fd25e02391a b55bd4c3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/24 15:06 android13-5.10-lts 7fd25e02391a b55bd4c3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/23 18:14 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/23 12:02 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/22 17:04 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/22 01:39 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/20 23:59 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/20 20:07 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/19 10:34 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/18 23:11 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/18 19:18 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/18 17:57 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/18 07:21 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/18 05:47 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/18 05:47 android13-5.10-lts e334a66065d3 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/16 17:25 android13-5.10-lts e334a66065d3 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
* Struck through repros no longer work on HEAD.