KASAN: use-after-free Write in l2tp_session_delete (2)

Status: auto-obsoleted due to no activity on 2025/08/08 12:20
Reported-by: syzbot+30bce2b97f6dbd70c939@syzkaller.appspotmail.com
First crash: 540d, last: 439d
▶ ▼ 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 (3) 22 5 195d 311d 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
android-6-1 KASAN: use-after-free Write in l2tp_session_delete (3) 22 3 23d 30d 0/2 premoderation: reported on 2026/06/24 03:10
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 756d 770d 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 1d18h 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 1177d 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 584d 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 16d 25d 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 249d 653d 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 758d 27/29 fixed on 2024/08/14 03:44

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: use-after-free in test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:70 [inline]
BUG: KASAN: use-after-free in l2tp_session_delete+0x24/0x4a0 net/l2tp/l2tp_core.c:1563
Write of size 8 at addr ffff8881047db008 by task kworker/u4:3/293

CPU: 0 PID: 293 Comm: kworker/u4:3 Not tainted 5.10.237-syzkaller-00309-g7e2543346ff7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x169/0x1d8 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+0xe2/0x130 mm/kasan/report.c:452
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x280/0x290 mm/kasan/generic.c:189
 __kasan_check_write+0x14/0x20 mm/kasan/shadow.c:37
 instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
 test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:70 [inline]
 l2tp_session_delete+0x24/0x4a0 net/l2tp/l2tp_core.c:1563
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1218 [inline]
 l2tp_tunnel_del_work+0x1d2/0x3e0 net/l2tp/l2tp_core.c:1258
 process_one_work+0x6e1/0xba0 kernel/workqueue.c:2301
 worker_thread+0xa6a/0x13b0 kernel/workqueue.c:2447
 kthread+0x346/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

Allocated by task 1100:
 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+0xda/0x110 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 __kmalloc+0x1a7/0x330 mm/slub.c:4033
 kmalloc include/linux/slab.h:557 [inline]
 kzalloc include/linux/slab.h:664 [inline]
 l2tp_session_create+0x39/0xb60 net/l2tp/l2tp_core.c:1599
 pppol2tp_connect+0xb35/0x1570 net/l2tp/l2tp_ppp.c:782
 __sys_connect_file net/socket.c:1866 [inline]
 __sys_connect+0x38c/0x410 net/socket.c:1883
 __do_sys_connect net/socket.c:1893 [inline]
 __se_sys_connect net/socket.c:1890 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:1890
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Freed by task 19:
 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:1595 [inline]
 slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1621
 slab_free mm/slub.c:3203 [inline]
 kfree+0xc0/0x270 mm/slub.c:4191
 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
 l2tp_session_dec_refcount+0xb2/0x1a0 net/l2tp/l2tp_core.c:205
 pppol2tp_session_destruct+0xb1/0xf0 net/l2tp/l2tp_ppp.c:419
 __sk_destruct+0x53/0x600 net/core/sock.c:1813
 sk_destruct net/core/sock.c:1858 [inline]
 __sk_free+0x313/0x410 net/core/sock.c:1869
 sk_free+0x54/0x90 net/core/sock.c:1880
 sock_put include/net/sock.h:1858 [inline]
 pppol2tp_put_sk+0x7a/0xb0 net/l2tp/l2tp_ppp.c:402
 rcu_do_batch+0x4df/0xa80 kernel/rcu/tree.c:2494
 rcu_core+0x55f/0xd60 kernel/rcu/tree.c:2735
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748
 __do_softirq+0x255/0x563 kernel/softirq.c:309

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 kernel/rcu/tree.c:2976 [inline]
 call_rcu+0x105/0x1040 kernel/rcu/tree.c:3050
 pppol2tp_release+0x208/0x2d0 net/l2tp/l2tp_ppp.c:458
 __sock_release net/socket.c:597 [inline]
 sock_close+0xe0/0x270 net/socket.c:1286
 __fput+0x2fb/0x770 fs/file_table.c:281
 ____fput+0x15/0x20 fs/file_table.c:314
 task_work_run+0x127/0x190 kernel/task_work.c:189
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop+0xcb/0xe0 kernel/entry/common.c:172
 exit_to_user_mode_prepare kernel/entry/common.c:199 [inline]
 syscall_exit_to_user_mode+0x68/0x90 kernel/entry/common.c:274
 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

The buggy address belongs to the object at ffff8881047db000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 8 bytes inside of
 512-byte region [ffff8881047db000, ffff8881047db200)
The buggy address belongs to the page:
page:ffffea000411f600 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1047d8
head:ffffea000411f600 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, ts 1966378862, free_ts 0
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x179/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x2235/0x23d0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x268/0x5f0 mm/page_alloc.c:5349
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1808 [inline]
 new_slab+0x84/0x3f0 mm/slub.c:1869
 new_slab_objects mm/slub.c:2627 [inline]
 ___slab_alloc+0x2a6/0x450 mm/slub.c:2791
 __slab_alloc+0x63/0xa0 mm/slub.c:2831
 slab_alloc_node mm/slub.c:2913 [inline]
 slab_alloc mm/slub.c:2955 [inline]
 __kmalloc_track_caller+0x1ef/0x320 mm/slub.c:4536
 __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]
 nlmsg_new include/net/netlink.h:953 [inline]
 inet_netconf_notify_devconf+0x169/0x220 net/ipv4/devinet.c:2121
 __devinet_sysctl_register+0x324/0x390 net/ipv4/devinet.c:2605
 devinet_init_net+0x33e/0x5b0 net/ipv4/devinet.c:2726
 ops_init+0x1ba/0x4a0 net/core/net_namespace.c:144
 __register_pernet_operations net/core/net_namespace.c:1164 [inline]
 register_pernet_operations+0x294/0x950 net/core/net_namespace.c:1245
 register_pernet_subsys+0x28/0x40 net/core/net_namespace.c:1286
 devinet_init+0x28/0xf4 net/ipv4/devinet.c:2795
 ip_rt_init+0x28c/0x36f net/ipv4/route.c:3644
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8881047daf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8881047daf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8881047db000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff8881047db080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881047db100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/05/10 12:14 android13-5.10-lts 7e2543346ff7 77908e5f .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Write in l2tp_session_delete
2025/03/02 17:14 android13-5.10-lts 3f5f2283d684 c3901742 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Write in l2tp_session_delete
2025/01/30 03:11 android13-5.10-lts fbe98d68b6b3 afe4eff5 .config console log report info ci2-android-5-10 KASAN: use-after-free Write in l2tp_session_delete
* Struck through repros no longer work on HEAD.