KASAN: use-after-free Read in l2tp_tunnel_del_work

Status: upstream: reported C repro on 2026/08/15 11:07
Reported-by: syzbot+3943d3264ac43d828afd@syzkaller.appspotmail.com
First crash: 122d, last: 2d16h
▶ ▼ Bug presence (3)
Date Name Commit Repro Result
2026/09/03 android14-6.1 (ToT) a456b3ef5767 C Failed due to an error; will retry later
2026/09/03 lts (merge base) 25fcaef79489 C Didn't crash
2026/09/03 upstream (ToT) 940de590b839 C Didn't crash
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work 19 142 2d14h 109d 0/2 premoderation: reported on 2026/06/27 08:43
android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work 19 765 53m 113d 0/2 premoderation: reported on 2026/06/23 09:58
upstream KASAN: use-after-free Write in l2tp_tunnel_del_work (2) net 22 syz unreliable done 2 1342d 1408d 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 1777d 1772d 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 827d 841d 27/29 fixed on 2024/08/14 03:44

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in hlist_unhashed include/linux/list.h:854 [inline]
BUG: KASAN: use-after-free in hlist_del_init_rcu include/linux/rculist.h:183 [inline]
BUG: KASAN: use-after-free in l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1225 [inline]
BUG: KASAN: use-after-free in l2tp_tunnel_del_work+0xd8/0x410 net/l2tp/l2tp_core.c:1266
Read of size 8 at addr ffff888110709c80 by task kworker/u4:3/300

CPU: 1 PID: 300 Comm: kworker/u4:3 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:
 <TASK>
 __dump_stack+0x21/0x24 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x71/0x200 mm/kasan/report.c:316
 print_report+0x4a/0x60 mm/kasan/report.c:420
 kasan_report+0x122/0x150 mm/kasan/report.c:524
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:351
 hlist_unhashed include/linux/list.h:854 [inline]
 hlist_del_init_rcu include/linux/rculist.h:183 [inline]
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1225 [inline]
 l2tp_tunnel_del_work+0xd8/0x410 net/l2tp/l2tp_core.c:1266
 process_one_work+0x717/0xc30 kernel/workqueue.c:2302
 worker_thread+0xa4d/0x11d0 kernel/workqueue.c:2449
 kthread+0x281/0x320 kernel/kthread.c:386
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>

Allocated by task 306:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_alloc_info+0x1f/0x30 mm/kasan/generic.c:505
 ____kasan_kmalloc mm/kasan/common.c:380 [inline]
 __kasan_kmalloc+0x95/0xb0 mm/kasan/common.c:389
 kasan_kmalloc include/linux/kasan.h:212 [inline]
 __do_kmalloc_node mm/slab_common.c:938 [inline]
 __kmalloc+0xb4/0x1e0 mm/slab_common.c:951
 kmalloc include/linux/slab.h:568 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 l2tp_session_create+0x38/0xbd0 net/l2tp/l2tp_core.c:1609
 pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:771
 __sys_connect_file net/socket.c:2000 [inline]
 __sys_connect+0x3da/0x460 net/socket.c:2017
 __do_sys_connect net/socket.c:2027 [inline]
 __se_sys_connect net/socket.c:2024 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2024
 x64_sys_call+0x88d/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
 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 306:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:516
 ____kasan_slab_free+0x132/0x180 mm/kasan/common.c:242
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:250
 kasan_slab_free include/linux/kasan.h:178 [inline]
 slab_free_hook mm/slub.c:1750 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1776
 slab_free mm/slub.c:3712 [inline]
 __kmem_cache_free+0xb7/0x1b0 mm/slub.c:3728
 kfree+0x6f/0xf0 mm/slab_common.c:990
 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
 l2tp_session_put+0xaf/0x1a0 net/l2tp/l2tp_core.c:193
 pppol2tp_ioctl+0x748/0x960 net/l2tp/l2tp_ppp.c:-1
 pppox_ioctl+0x1f6/0x330 drivers/net/ppp/pppox.c:93
 sock_do_ioctl+0x114/0x330 net/socket.c:1191
 sock_ioctl+0x475/0x700 net/socket.c:1310
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0x12f/0x1b0 fs/ioctl.c:856
 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:856
 x64_sys_call+0x58b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:17
 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

The buggy address belongs to the object at ffff888110709c00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
 512-byte region [ffff888110709c00, ffff888110709e00)

The buggy address belongs to the physical page:
page:ffffea000441c200 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888110708400 pfn:0x110708
head:ffffea000441c200 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 dead000000000001 ffff888100042f00
raw: ffff888110708400 000000008010000e 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 91, tgid 91 (klogd), ts 4469542077, free_ts 0
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2672
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2679
 get_page_from_freelist+0x2ca9/0x2d20 mm/page_alloc.c:4586
 __alloc_pages+0x1fa/0x610 mm/page_alloc.c:5930
 alloc_slab_page+0x6e/0xf0 include/linux/gfp.h:-1
 allocate_slab mm/slub.c:1967 [inline]
 new_slab+0x98/0x3e0 mm/slub.c:2020
 ___slab_alloc+0x70f/0xb70 mm/slub.c:3177
 __slab_alloc+0x5e/0xa0 mm/slub.c:3263
 slab_alloc_node mm/slub.c:3348 [inline]
 __kmem_cache_alloc_node+0x204/0x2d0 mm/slub.c:3423
 __do_kmalloc_node mm/slab_common.c:937 [inline]
 __kmalloc_node_track_caller+0xa1/0x1e0 mm/slab_common.c:958
 kmalloc_reserve net/core/skbuff.c:449 [inline]
 __alloc_skb+0x226/0x4a0 net/core/skbuff.c:518
 alloc_skb include/linux/skbuff.h:1322 [inline]
 alloc_skb_with_frags+0xa8/0x620 net/core/skbuff.c:6176
 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2761
 unix_dgram_sendmsg+0x5c1/0x1710 net/unix/af_unix.c:1947
 sock_sendmsg_nosec net/socket.c:716 [inline]
 __sock_sendmsg net/socket.c:728 [inline]
 __sys_sendto+0x4ac/0x660 net/socket.c:2142
 __do_sys_sendto net/socket.c:2154 [inline]
 __se_sys_sendto net/socket.c:2150 [inline]
 __x64_sys_sendto+0xe5/0x100 net/socket.c:2150
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888110709b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888110709c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888110709c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888110709d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888110709d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (110):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/15 10:59 android14-6.1 92668decd5e0 746171ee .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/12 09:39 android14-6.1 9ea8d8374e5e 4f92358f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/12 00:27 android14-6.1 9ea8d8374e5e 4f92358f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/10 20:52 android14-6.1 9ea8d8374e5e 4f92358f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/09 15:14 android14-6.1 9ea8d8374e5e b2734a59 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/07 20:07 android14-6.1 3b0884642a50 6520ecdb .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/07 08:07 android14-6.1 3b0884642a50 f7710056 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/07 04:43 android14-6.1 3b0884642a50 f7710056 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/06 17:28 android14-6.1 3b0884642a50 f7710056 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/06 13:37 android14-6.1 3b0884642a50 f7710056 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/05 09:02 android14-6.1 6612ef9d0b09 57bbd979 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/05 03:52 android14-6.1 6612ef9d0b09 57bbd979 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/03 18:34 android14-6.1 6612ef9d0b09 57bbd979 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/01 22:17 android14-6.1 6612ef9d0b09 f5cdae2f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/10/01 04:17 android14-6.1 317cdf044ecb 38f7f0d1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/28 18:11 android14-6.1 3d4bd33f0b0b a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/28 13:05 android14-6.1 3d4bd33f0b0b a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/28 11:15 android14-6.1 3d4bd33f0b0b a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/28 05:40 android14-6.1 3d4bd33f0b0b a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/27 21:56 android14-6.1 3d4bd33f0b0b a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/27 17:43 android14-6.1 3d4bd33f0b0b a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/27 13:34 android14-6.1 3d4bd33f0b0b a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/27 02:14 android14-6.1 3d4bd33f0b0b a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/24 00:29 android14-6.1 f26a1f4f9013 abce1216 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/20 10:54 android14-6.1 8cef8b5b11b7 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 23:50 android14-6.1 8cef8b5b11b7 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 22:15 android14-6.1 8cef8b5b11b7 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/16 22:19 android14-6.1 17514ea4a941 12a0a44a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/16 13:05 android14-6.1 c5dd09d80de6 12a0a44a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/13 22:31 android14-6.1 6308d6d3f1b1 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/13 08:11 android14-6.1 6308d6d3f1b1 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/13 06:00 android14-6.1 6308d6d3f1b1 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/13 03:15 android14-6.1 6308d6d3f1b1 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/12 20:34 android14-6.1 6308d6d3f1b1 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/10 23:49 android14-6.1 945be0af8244 1fe56c0a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/23 09:21 android14-6.1 92668decd5e0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/21 20:17 android14-6.1 92668decd5e0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/21 12:06 android14-6.1 92668decd5e0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/20 12:21 android14-6.1 92668decd5e0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/20 04:36 android14-6.1 92668decd5e0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/19 19:24 android14-6.1 92668decd5e0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/19 09:04 android14-6.1 92668decd5e0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/19 00:11 android14-6.1 92668decd5e0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/16 11:46 android14-6.1 92668decd5e0 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/15 20:08 android14-6.1 92668decd5e0 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/15 17:02 android14-6.1 92668decd5e0 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/15 10:22 android14-6.1 92668decd5e0 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/13 12:10 android14-6.1 92668decd5e0 359b2492 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/08 20:16 android14-6.1 92668decd5e0 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
* Struck through repros no longer work on HEAD.