KASAN: use-after-free Read in l2tp_tunnel_del_work

Status: premoderation: reported on 2026/06/27 08:43
Reported-by: syzbot+31aa91209c33be05babb@syzkaller.appspotmail.com
First crash: 85d, last: 13h46m
▶ ▼ 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 80 11h09m 36d 0/2 upstream: reported C repro on 2026/08/15 11:07
android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work 19 446 1h42m 89d 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 1318d 1384d 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 1753d 1748d 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 803d 817d 27/29 fixed on 2024/08/14 03:44

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in hlist_unhashed include/linux/list.h:826 [inline]
BUG: KASAN: use-after-free in hlist_del_init include/linux/list.h:883 [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 ffff888128ef9880 by task kworker/u4:5/366

CPU: 1 PID: 366 Comm: kworker/u4:5 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+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0x10f/0x150 mm/kasan/report.c:444
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309
 hlist_unhashed include/linux/list.h:826 [inline]
 hlist_del_init include/linux/list.h:883 [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+0x6c8/0xbb0 kernel/workqueue.c:2328
 worker_thread+0xaa0/0x1250 kernel/workqueue.c:2475
 kthread+0x3f5/0x4f0 kernel/kthread.c:337
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Allocated by task 1891:
 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:433 [inline]
 ____kasan_kmalloc mm/kasan/common.c:512 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:521
 kasan_kmalloc include/linux/kasan.h:227 [inline]
 __kmalloc+0x13d/0x2c0 mm/slub.c:4436
 kmalloc include/linux/slab.h:624 [inline]
 kzalloc include/linux/slab.h:750 [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:1923 [inline]
 __sys_connect+0x3cb/0x450 net/socket.c:1940
 __do_sys_connect net/socket.c:1950 [inline]
 __se_sys_connect net/socket.c:1947 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:1947
 x64_sys_call+0x7c/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Freed by task 1891:
 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:365
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
 kasan_slab_free include/linux/kasan.h:193 [inline]
 slab_free_hook mm/slub.c:1728 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1754
 slab_free mm/slub.c:3526 [inline]
 kfree+0xc4/0x270 mm/slub.c:4588
 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+0x1e4/0x320 drivers/net/ppp/pppox.c:93
 sock_do_ioctl+0x103/0x310 net/socket.c:1138
 sock_ioctl+0x459/0x6d0 net/socket.c:1257
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0x121/0x1a0 fs/ioctl.c:860
 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:860
 x64_sys_call+0x2f/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 __call_rcu_common kernel/rcu/tree.c:3011 [inline]
 call_rcu+0x10b/0xf60 kernel/rcu/tree.c:3129
 fib6_info_release include/net/ip6_fib.h:349 [inline]
 fib6_del_route net/ipv6/ip6_fib.c:1998 [inline]
 fib6_del+0xbf0/0xf00 net/ipv6/ip6_fib.c:2031
 fib6_clean_node+0x2a1/0x540 net/ipv6/ip6_fib.c:2193
 fib6_walk_continue+0x54b/0x740 net/ipv6/ip6_fib.c:2115
 fib6_walk+0x153/0x290 net/ipv6/ip6_fib.c:2163
 fib6_clean_tree net/ipv6/ip6_fib.c:2243 [inline]
 __fib6_clean_all net/ipv6/ip6_fib.c:2259 [inline]
 fib6_clean_all+0x1a1/0x270 net/ipv6/ip6_fib.c:2270
 rt6_sync_down_dev net/ipv6/route.c:4906 [inline]
 rt6_disable_ip+0x12a/0x840 net/ipv6/route.c:4911
 addrconf_ifdown+0x144/0x1910 net/ipv6/addrconf.c:3809
 addrconf_notify+0x3bd/0xe00 net/ipv6/addrconf.c:-1
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:391
 call_netdevice_notifiers_info net/core/dev.c:2070 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2082 [inline]
 call_netdevice_notifiers net/core/dev.c:2096 [inline]
 dev_close_many+0x325/0x4d0 net/core/dev.c:1671
 unregister_netdevice_many+0x477/0x1a00 net/core/dev.c:11152
 ip6gre_exit_batch_net+0x5ca/0x620 net/ipv6/ip6_gre.c:1657
 ops_exit_list net/core/net_namespace.c:177 [inline]
 cleanup_net+0x605/0xae0 net/core/net_namespace.c:599
 process_one_work+0x6c8/0xbb0 kernel/workqueue.c:2328
 worker_thread+0xaa0/0x1250 kernel/workqueue.c:2475
 kthread+0x3f5/0x4f0 kernel/kthread.c:337
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

The buggy address belongs to the object at ffff888128ef9800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
 512-byte region [ffff888128ef9800, ffff888128ef9a00)
The buggy address belongs to the page:
page:ffffea0004a3be00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x128ef8
head:ffffea0004a3be00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004649e00 0000000400000004 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 287, ts 24500375452, free_ts 0
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2607
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2613
 get_page_from_freelist+0x2c3a/0x2cd0 mm/page_alloc.c:4487
 __alloc_pages+0x1a2/0x460 mm/page_alloc.c:5824
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1937 [inline]
 new_slab+0xa0/0x4d0 mm/slub.c:2000
 ___slab_alloc+0x3ac/0x840 mm/slub.c:3033
 __slab_alloc+0x49/0x90 mm/slub.c:3120
 slab_alloc_node mm/slub.c:3211 [inline]
 slab_alloc mm/slub.c:3255 [inline]
 kmem_cache_alloc_trace+0x146/0x270 mm/slub.c:3272
 kmalloc include/linux/slab.h:619 [inline]
 kzalloc include/linux/slab.h:750 [inline]
 ipv6_add_addr+0x408/0xd90 net/ipv6/addrconf.c:1119
 inet6_addr_add+0x446/0x9d0 net/ipv6/addrconf.c:3032
 inet6_rtm_newaddr+0x6e7/0x9c0 net/ipv6/addrconf.c:4985
 rtnetlink_rcv_msg+0x9fd/0xcb0 net/core/rtnetlink.c:5662
 netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2520
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5680
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x86c/0xa30 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x879/0xb80 net/netlink/af_netlink.c:1923
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888128ef9780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888128ef9800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888128ef9880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888128ef9900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888128ef9980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (104):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/20 08:17 android13-5.15-lts 5bfe2b8c1439 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/20 06:57 android13-5.15-lts 5bfe2b8c1439 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 18:24 android13-5.15-lts 5bfe2b8c1439 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 08:05 android13-5.15-lts 5bfe2b8c1439 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/18 18:38 android13-5.15-lts 5bfe2b8c1439 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/15 08:38 android13-5.15-lts 5bfe2b8c1439 81a27d1a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 09:59 android13-5.15-lts 5bfe2b8c1439 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 01:37 android13-5.15-lts 5bfe2b8c1439 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/12 23:26 android13-5.15-lts 5bfe2b8c1439 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/06 18:14 android13-5.15-lts e9b8a6529ffa 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/06 00:35 android13-5.15-lts e9b8a6529ffa 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/05 23:15 android13-5.15-lts e9b8a6529ffa 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/04 08:36 android13-5.15-lts e9b8a6529ffa 801f0966 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/03 03:10 android13-5.15-lts 3af1e5c20882 85995287 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/03 01:00 android13-5.15-lts 3af1e5c20882 85995287 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/02 04:01 android13-5.15-lts 7f9a109e0767 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 21:53 android13-5.15-lts 656ab6019045 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 18:28 android13-5.15-lts 656ab6019045 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 12:07 android13-5.15-lts 656ab6019045 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/01 03:38 android13-5.15-lts 54850912d011 316d9396 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/31 02:38 android13-5.15-lts 54850912d011 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/31 00:04 android13-5.15-lts 54850912d011 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/30 14:13 android13-5.15-lts 54850912d011 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/30 09:21 android13-5.15-lts 54850912d011 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/29 18:53 android13-5.15-lts 54850912d011 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/28 04:59 android13-5.15-lts 54850912d011 69a01293 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/27 01:55 android13-5.15-lts 771777348d20 a2b77b9e .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/26 21:37 android13-5.15-lts 771777348d20 a2b77b9e .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/23 14:08 android13-5.15-lts dd960aad97f0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/23 03:34 android13-5.15-lts dd960aad97f0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/22 22:50 android13-5.15-lts dd960aad97f0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/22 21:12 android13-5.15-lts dd960aad97f0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/22 19:51 android13-5.15-lts dd960aad97f0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/22 04:46 android13-5.15-lts dd960aad97f0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/21 09:49 android13-5.15-lts dd960aad97f0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/21 05:32 android13-5.15-lts dd960aad97f0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/20 16:24 android13-5.15-lts dd960aad97f0 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/17 04:37 android13-5.15-lts 54275df9611d 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/16 14:50 android13-5.15-lts 54275df9611d 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/15 23:01 android13-5.15-lts 54275df9611d 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/15 16:37 android13-5.15-lts 54275df9611d 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/14 16:30 android13-5.15-lts 54275df9611d 6f9b3e89 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/14 04:48 android13-5.15-lts 54275df9611d b13552fe .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/14 02:10 android13-5.15-lts 54275df9611d b13552fe .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/13 15:20 android13-5.15-lts 54275df9611d 359b2492 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/08/13 05:39 android13-5.15-lts 54275df9611d 359b2492 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 KASAN: use-after-free Read in l2tp_tunnel_del_work
* Struck through repros no longer work on HEAD.