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: 141d, last: 58m
▶ ▼ 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 131 1d18h 87d 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 19 164 7h22m 137d 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 1369d 1435d 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 1804d 1800d 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 854d 868d 27/29 fixed on 2024/08/14 03:44

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in hlist_unhashed include/linux/list.h:815 [inline]
BUG: KASAN: use-after-free in hlist_del_init include/linux/list.h:872 [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 ffff888112b4f880 by task kworker/u4:3/301

CPU: 1 PID: 301 Comm: kworker/u4:3 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026
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:815 [inline]
 hlist_del_init include/linux/list.h:872 [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 526:
 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 526:
 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+0x1e1/0x440 drivers/net/ppp/pppox.c:110
 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 ffff888112b4f800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
 512-byte region [ffff888112b4f800, ffff888112b4fa00)
The buggy address belongs to the page:
page:ffffea00044ad300 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x112b4c
head:ffffea00044ad300 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 524, ts 28080832233, free_ts 28052503227
 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]
 __kmalloc+0x1f9/0x330 mm/slub.c:4034
 __kmalloc_node include/linux/slab.h:421 [inline]
 kmalloc_node include/linux/slab.h:578 [inline]
 kzalloc_node include/linux/slab.h:678 [inline]
 qdisc_alloc+0x79/0x720 net/sched/sch_generic.c:865
 qdisc_create_dflt+0x6b/0x390 net/sched/sch_generic.c:928
 prio_tune+0x64e/0x1240 net/sched/sch_prio.c:198
 prio_init+0x6f/0x80 net/sched/sch_prio.c:242
 qdisc_create+0x84c/0x1220 net/sched/sch_api.c:1272
 tc_modify_qdisc+0x8c2/0x1470 net/sched/sch_api.c:-1
 rtnetlink_rcv_msg+0x9e9/0xca0 net/core/rtnetlink.c:5622
 netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2508
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5640
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 __free_pages_ok+0x80b/0x830 mm/page_alloc.c:1629
 free_the_page mm/page_alloc.c:5445 [inline]
 __free_pages+0xd8/0x390 mm/page_alloc.c:5454
 free_pages+0x82/0x90 mm/page_alloc.c:5465
 __stack_depot_save+0x492/0x4c0 lib/stackdepot.c:359
 kasan_save_stack mm/kasan/common.c:39 [inline]
 kasan_set_track+0x5b/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
 incfs_free_bfc+0x62/0x70 fs/incfs/format.c:42
 incfs_open_data_file+0x375/0x550 fs/incfs/data_mgmt.c:327
 make_inode_ready_for_data_ops+0x127/0x1b0 fs/incfs/data_mgmt.c:385
 file_open+0x3d0/0x680 fs/incfs/vfs.c:1503
 do_dentry_open+0x7a5/0x10a0 fs/open.c:819
 vfs_open+0x73/0x80 fs/open.c:944

Memory state around the buggy address:
 ffff888112b4f780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888112b4f800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888112b4f880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888112b4f900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888112b4f980: 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: 1 PID: 301 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Modules linked in:

CPU: 1 PID: 301 Comm: kworker/u4:3 Tainted: G    B             syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/06/2026
Workqueue: l2tp l2tp_tunnel_del_work
RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28
Code: 04 01 48 c7 c7 00 53 40 85 e8 5c 0e 3c 02 0f 0b eb c3 e8 63 80 26 ff c6 05 22 70 82 04 01 48 c7 c7 60 53 40 85 e8 40 0e 3c 02 <0f> 0b eb a7 e8 47 80 26 ff c6 05 03 70 82 04 01 48 c7 c7 80 52 40
RSP: 0018:ffffc90007987c58 EFLAGS: 00010246
RAX: e3a5e2180bbe6100 RBX: 0000000000000003 RCX: ffff88812750d000
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: ffffc90007987c68 R08: ffff8881f7152fff R09: 1ffff1103ee2a5ff
R10: dffffc0000000000 R11: ffffed103ee2a600 R12: ffff888112b4ec20
R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9024bfd060 CR3: 000000010d46f000 CR4: 00000000003506a0
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 50357a8fe3be37a6 ]---

Crashes (963):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/11/11 09:23 android13-5.10-lts c73351b2e985 d3056657 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/11 09:23 android13-5.10-lts c73351b2e985 d3056657 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/11 03:35 android13-5.10-lts f61a392235e0 d3056657 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/10 14:43 android13-5.10-lts f61a392235e0 d3056657 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/10 10:34 android13-5.10-lts f61a392235e0 70ec0380 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/10 04:13 android13-5.10-lts f61a392235e0 70ec0380 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/10 02:29 android13-5.10-lts f61a392235e0 70ec0380 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/09 23:27 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/09 22:26 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/09 15:53 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/09 10:07 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/09 08:37 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/09 03:32 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/08 23:23 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/08 15:25 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/08 05:19 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/08 02:03 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/07 22:13 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/07 21:04 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/07 19:05 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/07 14:05 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/07 12:26 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/07 07:16 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/07 04:02 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/06 23:55 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/06 18:14 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/06 16:40 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/06 13:19 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/06 08:49 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/06 06:58 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/05 23:17 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/05 21:29 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/05 20:23 android13-5.10-lts f61a392235e0 5cecaf1f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/05 17:35 android13-5.10-lts f61a392235e0 2ee8459f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/05 06:56 android13-5.10-lts f61a392235e0 2ee8459f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/05 02:41 android13-5.10-lts f61a392235e0 73438ed0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/04 20:43 android13-5.10-lts f61a392235e0 73438ed0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/04 15:21 android13-5.10-lts f61a392235e0 73438ed0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/04 12:07 android13-5.10-lts f61a392235e0 5af5b6c6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/04 03:09 android13-5.10-lts f61a392235e0 5af5b6c6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/04 03:09 android13-5.10-lts f61a392235e0 5af5b6c6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/11/03 21:05 android13-5.10-lts f61a392235e0 e2d35131 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/29 11:40 android13-5.10-lts 340d402887d3 7bf4ea23 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/26 18:53 android13-5.10-lts c5d8ec7afea2 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 general protection fault in l2tp_tunnel_del_work
* Struck through repros no longer work on HEAD.