KASAN: use-after-free Read in l2tp_tunnel_del_work

Status: premoderation: reported on 2026/06/14 19:53
Reported-by: syzbot+0619f828e4997cb7bb88@syzkaller.appspotmail.com
First crash: 43d, last: 10h47m
▶ ▼ 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 20 16h29m 30d 0/2 premoderation: reported on 2026/06/27 08:43
android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work 19 60 12h04m 34d 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 1263d 1329d 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 1698d 1693d 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 C done 99 748d 762d 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 ffff888132807480 by task kworker/u4:3/201

CPU: 0 PID: 201 Comm: kworker/u4:3 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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 1212:
 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 1212:
 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

Last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
 __call_rcu_common kernel/rcu/tree.c:2807 [inline]
 call_rcu+0xcf/0xf50 kernel/rcu/tree.c:2926
 fib6_info_release include/net/ip6_fib.h:350 [inline]
 ip6_route_info_create+0xaa8/0x14d0 net/ipv6/route.c:3878
 ip6_route_add+0x27/0x130 net/ipv6/route.c:3892
 addrconf_prefix_route+0x233/0x310 net/ipv6/addrconf.c:2466
 inet6_addr_add+0x527/0x9c0 net/ipv6/addrconf.c:3042
 inet6_rtm_newaddr+0x74a/0xa10 net/ipv6/addrconf.c:4999
 rtnetlink_rcv_msg+0xb28/0xde0 net/core/rtnetlink.c:6153
 netlink_rcv_skb+0x200/0x450 net/netlink/af_netlink.c:2521
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:6171
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x8c1/0xa60 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x8b9/0xbd0 net/netlink/af_netlink.c:1873
 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
 x64_sys_call+0x83/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:45
 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 ffff888132807400
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
 512-byte region [ffff888132807400, ffff888132807600)

The buggy address belongs to the physical page:
page:ffffea0004ca0100 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x132804
head:ffffea0004ca0100 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100042f00
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 294, tgid 294 (syz-executor), ts 23003504724, 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]
 netlink_alloc_large_skb net/netlink/af_netlink.c:1183 [inline]
 netlink_sendmsg+0x635/0xbd0 net/netlink/af_netlink.c:1848
 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
 x64_sys_call+0x83/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888132807380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888132807400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888132807480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888132807500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888132807580: 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: 201 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:
CPU: 0 PID: 201 Comm: kworker/u4:3 Tainted: G    B   W          syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Workqueue: l2tp l2tp_tunnel_del_work
RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Code: 05 01 48 c7 c7 80 0c ca 85 e8 bc 28 d9 fe 0f 0b eb c3 e8 13 9a 08 ff c6 05 f4 c9 26 05 01 48 c7 c7 e0 0c ca 85 e8 a0 28 d9 fe <0f> 0b eb a7 e8 f7 99 08 ff c6 05 d5 c9 26 05 01 48 c7 c7 20 0c ca
RSP: 0018:ffffc90000aa7c38 EFLAGS: 00010246
RAX: be36f510757d8700 RBX: 0000000000000003 RCX: ffff88811fd86540
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: ffffc90000aa7c48 R08: ffffc90000aa7827 R09: 1ffff92000154f04
R10: dffffc0000000000 R11: fffff52000154f05 R12: 1ffff11026500e90
R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f053d528000 CR3: 000000000700f000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __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+0xc8/0x1a0 net/l2tp/l2tp_core.c:192
 l2tp_session_delete+0x3df/0x4d0 net/l2tp/l2tp_core.c:1582
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1228 [inline]
 l2tp_tunnel_del_work+0x199/0x410 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>
---[ end trace 0000000000000000 ]---

Crashes (35):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/27 09:11 android14-6.1 92668decd5e0 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/25 21:07 android14-6.1 92668decd5e0 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/25 17:12 android14-6.1 92668decd5e0 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/25 03:07 android14-6.1 92668decd5e0 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/25 03:06 android14-6.1 92668decd5e0 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/25 03:06 android14-6.1 92668decd5e0 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/25 03:06 android14-6.1 92668decd5e0 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/25 00:54 android14-6.1 92668decd5e0 dd737a83 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/23 21:20 android14-6.1 92668decd5e0 71a13572 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/23 21:14 android14-6.1 92668decd5e0 71a13572 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/23 01:40 android14-6.1 92668decd5e0 881ce5c2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/22 04:35 android14-6.1 72b456bf57ad b561ce9c .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/19 20:55 android14-6.1 c7e15f0bdc49 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/12 22:20 android14-6.1 21b931853e8d d78ea535 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/12 22:20 android14-6.1 21b931853e8d d78ea535 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/12 18:57 android14-6.1 21b931853e8d d78ea535 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/11 23:57 android14-6.1 21b931853e8d d78ea535 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/10 13:11 android14-6.1 52939c41021c 4167ee25 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/05 14:15 android14-6.1 cf4093a4ac64 fcece630 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/05 14:15 android14-6.1 cf4093a4ac64 fcece630 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/05 01:58 android14-6.1 cf4093a4ac64 fcece630 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/04 09:57 android14-6.1 cf4093a4ac64 fcece630 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/07/04 09:51 android14-6.1 cf4093a4ac64 fcece630 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/28 13:30 android14-6.1 83f1262811ad fb92f11c .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/28 10:58 android14-6.1 83f1262811ad fb92f11c .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/28 10:58 android14-6.1 83f1262811ad fb92f11c .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/27 10:54 android14-6.1 83f1262811ad fb92f11c .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/22 03:08 android14-6.1 72813af230c7 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/21 16:18 android14-6.1 72813af230c7 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/20 13:10 android14-6.1 72813af230c7 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/20 05:48 android14-6.1 9f35ca3ff66c 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/20 02:10 android14-6.1 9f35ca3ff66c 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/18 00:04 android14-6.1 9f35ca3ff66c b62b3ded .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/15 16:46 android14-6.1 f17c14b8ada7 50bb0618 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/06/14 19:52 android14-6.1 f17c14b8ada7 1d2f3589 .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.