KASAN: use-after-free Write in l2tp_session_delete (3)

Status: premoderation: reported on 2026/06/24 03:10
Reported-by: syzbot+132a8a4f164715afe387@syzkaller.appspotmail.com
First crash: 30d, last: 24d
▶ ▼ Similar bugs (14)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-10 KASAN: use-after-free Write in l2tp_session_delete 22 2 640d 664d 0/2 auto-obsoleted due to no activity on 2025/01/19 22:14
android-5-10 KASAN: use-after-free Write in l2tp_session_delete (2) 22 3 440d 540d 0/2 auto-obsoleted due to no activity on 2025/08/08 12:20
android-5-10 KASAN: use-after-free Write in l2tp_session_delete (3) 22 5 196d 312d 0/2 auto-obsoleted due to no activity on 2026/04/09 06:46
android-6-1 KASAN: use-after-free Write in l2tp_session_delete (2) 22 1 153d 153d 0/2 auto-obsoleted due to no activity on 2026/05/22 02:12
linux-6.1 KASAN: use-after-free Write in l2tp_session_delete (2) 22 1 185d 185d 0/3 auto-obsoleted due to no activity on 2026/04/29 20:48
linux-6.1 KASAN: use-after-free Write in l2tp_session_delete 22 2 672d 694d 0/3 auto-obsoleted due to no activity on 2024/12/29 03:40
android-5-15 KASAN: use-after-free Write in l2tp_session_delete 22 2 757d 771d 0/2 auto-obsoleted due to no activity on 2024/09/25 05:09
android-5-15 KASAN: use-after-free Write in l2tp_session_delete (2) origin:downstream 22 C error 29 2d10h 498d 0/2 upstream: reported C repro on 2025/03/13 02:24
linux-5.15 KASAN: use-after-free Write in l2tp_session_delete 22 2 1089d 1178d 0/3 auto-obsoleted due to no activity on 2023/11/08 00:22
linux-5.15 KASAN: use-after-free Write in l2tp_session_delete (2) 22 2 585d 672d 0/3 auto-obsoleted due to no activity on 2025/03/26 11:58
android-5-10 KASAN: use-after-free Write in l2tp_session_delete (4) 22 C 7 17d 26d 0/2 upstream: reported C repro on 2026/06/28 05:46
android-6-1 KASAN: use-after-free Write in l2tp_session_delete origin:downstream 22 syz error 20 250d 654d 0/2 auto-obsoleted due to no activity on 2026/02/14 16:29
linux-5.15 KASAN: use-after-free Write in l2tp_session_delete (3) 22 1 364d 364d 0/3 auto-obsoleted due to no activity on 2025/11/02 00:17
upstream KASAN: slab-use-after-free Write in l2tp_session_delete net 22 C done 1286 739d 759d 27/29 fixed on 2024/08/14 03:44

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:886 [inline]
BUG: KASAN: use-after-free in hlist_del_init_rcu include/linux/rculist.h:184 [inline]
BUG: KASAN: use-after-free in l2tp_session_unhash net/l2tp/l2tp_core.c:1197 [inline]
BUG: KASAN: use-after-free in l2tp_session_delete+0x13d/0x4d0 net/l2tp/l2tp_core.c:1577
Write of size 8 at addr ffff8881311bd880 by task syz.3.73/640

CPU: 0 PID: 640 Comm: syz.3.73 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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_store8_noabort+0x17/0x20 mm/kasan/report_generic.c:356
 __hlist_del include/linux/list.h:886 [inline]
 hlist_del_init_rcu include/linux/rculist.h:184 [inline]
 l2tp_session_unhash net/l2tp/l2tp_core.c:1197 [inline]
 l2tp_session_delete+0x13d/0x4d0 net/l2tp/l2tp_core.c:1577
 pppol2tp_release+0x169/0x2b0 net/l2tp/l2tp_ppp.c:438
 __sock_release net/socket.c:652 [inline]
 sock_close+0xc9/0x220 net/socket.c:1389
 __fput+0x1fd/0x8f0 fs/file_table.c:320
 ____fput+0x15/0x20 fs/file_table.c:348
 task_work_run+0x1e1/0x250 kernel/task_work.c:203
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop+0x9b/0xb0 kernel/entry/common.c:177
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:303
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fea48d9ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdd41b36a8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007fea49017da0 RCX: 00007fea48d9ce59
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007fea49017da0 R08: 00007fea49016038 R09: 0000000000000000
R10: 000000000003fcbc R11: 0000000000000246 R12: 00000000000099cc
R13: 00007fea4901609c R14: 00000000000096d4 R15: 00007fea49016090
 </TASK>

Allocated by task 641:
 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 643:
 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 ffff8881311bd800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
 512-byte region [ffff8881311bd800, ffff8881311bda00)

The buggy address belongs to the physical page:
page:ffffea0004c46f00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1311bc
head:ffffea0004c46f00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004c47200 dead000000000002 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 0xd2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 289, tgid 289 (syz-executor), ts 22782115145, 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]
 nlmsg_new include/net/netlink.h:987 [inline]
 fdb_notify+0x78/0x130 net/bridge/br_fdb.c:191
 fdb_add_local+0x16b/0x260 net/bridge/br_fdb.c:434
 br_fdb_change_mac_address+0x492/0x4d0 net/bridge/br_fdb.c:494
 br_device_event+0x14d/0x790 net/bridge/br.c:43
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xa1/0x110 kernel/notifier.c:455
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8881311bd780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8881311bd800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881311bd880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8881311bd900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881311bd980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 1 PID: 640 at net/l2tp/l2tp_ppp.c:156 pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Modules linked in:
CPU: 1 PID: 640 Comm: syz.3.73 Tainted: G    B              syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Code: 5d c3 e8 bc ba d5 fc be 02 00 00 00 eb 0a e8 b0 ba d5 fc be 01 00 00 00 4c 89 f7 e8 83 1d cd fd e9 0f ff ff ff e8 99 ba d5 fc <0f> 0b 48 89 df e8 ff 00 00 00 eb bd e8 88 ba d5 fc 4c 89 f7 be 03
RSP: 0018:ffffc9000f9c7cb0 EFLAGS: 00010293
RAX: ffffffff849ba997 RBX: ffff88810d911000 RCX: ffff888113c08000
RDX: 0000000000000000 RSI: 000000001524fbd0 RDI: 000000000c04eb7d
RBP: ffffc9000f9c7cd0 R08: ffff88810d911083 R09: 1ffff11021b22210
R10: dffffc0000000000 R11: ffffed1021b22211 R12: dffffc0000000000
R13: dffffc0000000000 R14: 000000001524fbd0 R15: ffff8881311bd800
FS:  0000555583d20500(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f66e29350f5 CR3: 00000001121c6000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:434
 __sock_release net/socket.c:652 [inline]
 sock_close+0xc9/0x220 net/socket.c:1389
 __fput+0x1fd/0x8f0 fs/file_table.c:320
 ____fput+0x15/0x20 fs/file_table.c:348
 task_work_run+0x1e1/0x250 kernel/task_work.c:203
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop+0x9b/0xb0 kernel/entry/common.c:177
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:303
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fea48d9ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdd41b36a8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007fea49017da0 RCX: 00007fea48d9ce59
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007fea49017da0 R08: 00007fea49016038 R09: 0000000000000000
R10: 000000000003fcbc R11: 0000000000000246 R12: 00000000000099cc
R13: 00007fea4901609c R14: 00000000000096d4 R15: 00007fea49016090
 </TASK>
---[ end trace 0000000000000000 ]---

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/30 13:12 android14-6.1 c98298656777 fff8d0a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Write in l2tp_session_delete
2026/06/28 18:14 android14-6.1 83f1262811ad fb92f11c .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Write in l2tp_session_delete
2026/06/24 03:09 android14-6.1 de145cc20dc6 042555ff .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Write in l2tp_session_delete
* Struck through repros no longer work on HEAD.