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: 89d, last: 38m
▶ ▼ 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 3h17m 36d 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 19 104 5h54m 85d 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 1317d 1383d 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 1752d 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:808 [inline]
BUG: KASAN: use-after-free in hlist_del_init include/linux/list.h:865 [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 ffff888117fd7880 by task kworker/u4:1/9

CPU: 1 PID: 9 Comm: kworker/u4:1 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:
 __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:808 [inline]
 hlist_del_init include/linux/list.h:865 [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 604:
 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 603:
 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+0x1e4/0x320 drivers/net/ppp/pppox.c:93
 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 ffff888117fd7800
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 128 bytes inside of
 512-byte region [ffff888117fd7800, ffff888117fd7a00)
The buggy address belongs to the page:
page:ffffea00045ff500 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x117fd4
head:ffffea00045ff500 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 400, ts 31564751041, free_ts 31556228878
 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_track_caller+0x1e4/0x310 mm/slub.c:4541
 __kmalloc_reserve net/core/skbuff.c:144 [inline]
 __alloc_skb+0xdc/0x520 net/core/skbuff.c:212
 alloc_skb include/linux/skbuff.h:1126 [inline]
 alloc_skb_with_frags+0xa3/0x560 net/core/skbuff.c:6045
 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2392
 unix_dgram_sendmsg+0x6f3/0x18f0 net/unix/af_unix.c:1725
 sock_sendmsg_nosec net/socket.c:652 [inline]
 __sock_sendmsg net/socket.c:664 [inline]
 sock_write_iter+0x2a6/0x3a0 net/socket.c:1019
 call_write_iter include/linux/fs.h:2072 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x770/0xd70 fs/read_write.c:605
 ksys_write+0x14a/0x260 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:667
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
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]
 kmem_cache_free+0x100/0x2d0 mm/slub.c:3224
 kernfs_put+0x315/0x480 fs/kernfs/dir.c:547
 kernfs_remove_by_name_ns+0xea/0x160 fs/kernfs/dir.c:1599
 kernfs_remove_by_name include/linux/kernfs.h:623 [inline]
 sysfs_unmerge_group+0xd3/0x130 fs/sysfs/group.c:369
 rpm_sysfs_remove drivers/base/power/sysfs.c:826 [inline]
 dpm_sysfs_remove+0x77/0xc0 drivers/base/power/sysfs.c:835
 device_del+0x270/0xe60 drivers/base/core.c:3430
 device_unregister+0x15/0x40 drivers/base/core.c:3497

Memory state around the buggy address:
 ffff888117fd7780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888117fd7800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888117fd7880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888117fd7900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888117fd7980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (443):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/20 13:12 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/20 09:37 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/20 06:34 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/20 04:52 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/20 03:39 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/20 01:42 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 21:50 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 20:24 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 18:23 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 15:18 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 08:50 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 01:27 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/19 00:10 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/18 22:22 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/18 21:10 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/18 12:16 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/18 12:06 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/18 07:38 android13-5.10-lts 452567d1985b 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/17 22:02 android13-5.10-lts 452567d1985b 8d7d05f1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/17 21:01 android13-5.10-lts 452567d1985b 8d7d05f1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/17 19:35 android13-5.10-lts 452567d1985b 8d7d05f1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/17 17:17 android13-5.10-lts 452567d1985b 8d7d05f1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/17 13:26 android13-5.10-lts 452567d1985b 95928915 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/17 02:32 android13-5.10-lts 452567d1985b 95928915 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/16 23:27 android13-5.10-lts 452567d1985b 95928915 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/16 23:27 android13-5.10-lts 452567d1985b 95928915 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/16 19:54 android13-5.10-lts 452567d1985b 12a0a44a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/16 13:23 android13-5.10-lts 452567d1985b 12a0a44a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/16 11:49 android13-5.10-lts 452567d1985b 12a0a44a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/16 09:04 android13-5.10-lts 452567d1985b 12a0a44a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/16 05:02 android13-5.10-lts 452567d1985b 12a0a44a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/15 21:59 android13-5.10-lts 452567d1985b 2daa4bb5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/15 18:40 android13-5.10-lts 452567d1985b 2daa4bb5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/15 14:37 android13-5.10-lts 452567d1985b 2daa4bb5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/15 07:30 android13-5.10-lts 452567d1985b 81a27d1a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/15 04:24 android13-5.10-lts 452567d1985b 81a27d1a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 22:19 android13-5.10-lts 452567d1985b 81a27d1a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 21:45 android13-5.10-lts 452567d1985b 81a27d1a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 13:26 android13-5.10-lts 452567d1985b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 11:48 android13-5.10-lts 452567d1985b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 09:51 android13-5.10-lts 452567d1985b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 07:35 android13-5.10-lts 452567d1985b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 06:10 android13-5.10-lts 452567d1985b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
2026/09/14 04:34 android13-5.10-lts 452567d1985b 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in l2tp_tunnel_del_work
* Struck through repros no longer work on HEAD.