KASAN: use-after-free Write in l2tp_session_delete

Status: auto-obsoleted due to no activity on 2024/12/29 03:40
Reported-by: syzbot+d6124878d94deac1fbaa@syzkaller.appspotmail.com
First crash: 696d, last: 674d
▶ ▼ 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 642d 666d 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 441d 542d 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 198d 314d 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 155d 155d 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 25d 32d 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 187d 187d 0/3 auto-obsoleted due to no activity on 2026/04/29 20:48
android-5-15 KASAN: use-after-free Write in l2tp_session_delete 22 2 759d 772d 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 3d20h 500d 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 1091d 1179d 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 586d 674d 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 18d 28d 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 251d 655d 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 366d 366d 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 741d 760d 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:102 [inline]
BUG: KASAN: use-after-free in test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:71 [inline]
BUG: KASAN: use-after-free in l2tp_session_delete+0x21/0x600 net/l2tp/l2tp_core.c:1561
Write of size 8 at addr ffff88805b7b7808 by task kworker/u4:2/33

CPU: 0 PID: 33 Comm: kworker/u4:2 Not tainted 6.1.111-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:284 [inline]
 print_report+0x15f/0x4f0 mm/kasan/report.c:395
 kasan_report+0x136/0x160 mm/kasan/report.c:495
 kasan_check_range+0x27f/0x290 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 test_and_set_bit include/asm-generic/bitops/instrumented-atomic.h:71 [inline]
 l2tp_session_delete+0x21/0x600 net/l2tp/l2tp_core.c:1561
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1216 [inline]
 l2tp_tunnel_del_work+0x1ee/0x3b0 net/l2tp/l2tp_core.c:1256
 process_one_work+0x8a9/0x11d0 kernel/workqueue.c:2292
 worker_thread+0xa47/0x1200 kernel/workqueue.c:2439
 kthread+0x28d/0x320 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>

Allocated by task 4161:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x97/0xb0 mm/kasan/common.c:383
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:936 [inline]
 __kmalloc+0xb2/0x230 mm/slab_common.c:949
 kmalloc include/linux/slab.h:562 [inline]
 kzalloc include/linux/slab.h:693 [inline]
 l2tp_session_create+0x37/0xb30 net/l2tp/l2tp_core.c:1597
 pppol2tp_connect+0xc3d/0x1720 net/l2tp/l2tp_ppp.c:781
 __sys_connect_file net/socket.c:2006 [inline]
 __sys_connect+0x2c9/0x300 net/socket.c:2023
 __do_sys_connect net/socket.c:2033 [inline]
 __se_sys_connect net/socket.c:2030 [inline]
 __x64_sys_connect+0x76/0x80 net/socket.c:2030
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 4175:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
 kasan_save_free_info+0x27/0x40 mm/kasan/generic.c:516
 ____kasan_slab_free+0xd6/0x120 mm/kasan/common.c:236
 kasan_slab_free include/linux/kasan.h:177 [inline]
 slab_free_hook mm/slub.c:1724 [inline]
 slab_free_freelist_hook mm/slub.c:1750 [inline]
 slab_free mm/slub.c:3661 [inline]
 __kmem_cache_free+0x25c/0x3c0 mm/slub.c:3674
 __sk_destruct+0x50/0x5f0 net/core/sock.c:2139
 rcu_do_batch kernel/rcu/tree.c:2297 [inline]
 rcu_core+0xade/0x1820 kernel/rcu/tree.c:2557
 handle_softirqs+0x2ee/0xa40 kernel/softirq.c:571
 __do_softirq kernel/softirq.c:605 [inline]
 invoke_softirq kernel/softirq.c:445 [inline]
 __irq_exit_rcu+0x157/0x240 kernel/softirq.c:654
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:666
 sysvec_apic_timer_interrupt+0x91/0xb0 arch/x86/kernel/apic/apic.c:1106
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:653

Last potentially related work creation:
 kasan_save_stack+0x3b/0x60 mm/kasan/common.c:45
 __kasan_record_aux_stack+0xb0/0xc0 mm/kasan/generic.c:486
 call_rcu+0x163/0xa10 kernel/rcu/tree.c:2845
 pppol2tp_release+0x247/0x340 net/l2tp/l2tp_ppp.c:457
 __sock_release net/socket.c:654 [inline]
 sock_close+0xcd/0x230 net/socket.c:1400
 __fput+0x3f6/0x8d0 fs/file_table.c:320
 task_work_run+0x246/0x300 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0xa73/0x26a0 kernel/exit.c:871
 do_group_exit+0x202/0x2b0 kernel/exit.c:1021
 get_signal+0x16f7/0x17d0 kernel/signal.c:2870
 arch_do_signal_or_restart+0xb0/0x1a10 arch/x86/kernel/signal.c:871
 exit_to_user_mode_loop+0x6a/0x100 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
 syscall_exit_to_user_mode+0x60/0x270 kernel/entry/common.c:303
 do_syscall_64+0x47/0xb0 arch/x86/entry/common.c:87
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Second to last potentially related work creation:
 kasan_save_stack+0x3b/0x60 mm/kasan/common.c:45
 __kasan_record_aux_stack+0xb0/0xc0 mm/kasan/generic.c:486
 call_rcu+0x163/0xa10 kernel/rcu/tree.c:2845
 qdisc_put net/sched/sch_generic.c:1095 [inline]
 dev_shutdown+0x359/0x440 net/sched/sch_generic.c:1483
 unregister_netdevice_many+0xaac/0x17a0 net/core/dev.c:10873
 ip6gre_exit_batch_net+0x415/0x460 net/ipv6/ip6_gre.c:1669
 ops_exit_list net/core/net_namespace.c:177 [inline]
 cleanup_net+0x763/0xb60 net/core/net_namespace.c:604
 process_one_work+0x8a9/0x11d0 kernel/workqueue.c:2292
 worker_thread+0xa47/0x1200 kernel/workqueue.c:2439
 kthread+0x28d/0x320 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

The buggy address belongs to the object at ffff88805b7b7800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 8 bytes inside of
 1024-byte region [ffff88805b7b7800, ffff88805b7b7c00)

The buggy address belongs to the physical page:
page:ffffea00016dec00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5b7b0
head:ffffea00016dec00 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000001 ffff888017c41dc0
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 3641, tgid 3641 (syz-executor), ts 72120467541, free_ts 18303717872
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x18d/0x1b0 mm/page_alloc.c:2517
 prep_new_page mm/page_alloc.c:2524 [inline]
 get_page_from_freelist+0x322e/0x33b0 mm/page_alloc.c:4290
 __alloc_pages+0x28d/0x770 mm/page_alloc.c:5558
 alloc_slab_page+0x6a/0x150 mm/slub.c:1794
 allocate_slab mm/slub.c:1939 [inline]
 new_slab+0x84/0x2d0 mm/slub.c:1992
 ___slab_alloc+0xc20/0x1270 mm/slub.c:3180
 __slab_alloc mm/slub.c:3279 [inline]
 slab_alloc_node mm/slub.c:3364 [inline]
 __kmem_cache_alloc_node+0x19f/0x260 mm/slub.c:3437
 __do_kmalloc_node mm/slab_common.c:935 [inline]
 __kmalloc_node_track_caller+0xa0/0x220 mm/slab_common.c:956
 kmalloc_reserve net/core/skbuff.c:446 [inline]
 __alloc_skb+0x135/0x670 net/core/skbuff.c:515
 alloc_skb include/linux/skbuff.h:1271 [inline]
 nlmsg_new include/net/netlink.h:991 [inline]
 rtmsg_fib+0x140/0x620 net/ipv4/fib_semantics.c:522
 fib_table_insert+0xfb6/0x1f20 net/ipv4/fib_trie.c:1404
 fib_magic net/ipv4/fib_frontend.c:1104 [inline]
 fib_add_ifaddr+0xf4c/0x1730 net/ipv4/fib_frontend.c:1148
 fib_netdev_event+0x620/0x730 net/ipv4/fib_frontend.c:1486
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xd0/0x170 kernel/notifier.c:455
 __dev_notify_flags+0x304/0x610
 dev_change_flags+0xe7/0x190 net/core/dev.c:8661
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1444 [inline]
 free_pcp_prepare mm/page_alloc.c:1494 [inline]
 free_unref_page_prepare+0xf63/0x1120 mm/page_alloc.c:3369
 free_unref_page+0x33/0x3e0 mm/page_alloc.c:3464
 free_contig_range+0x9a/0x150 mm/page_alloc.c:9518
 destroy_args+0xfe/0x997 mm/debug_vm_pgtable.c:1031
 debug_vm_pgtable+0x416/0x46b mm/debug_vm_pgtable.c:1354
 do_one_initcall+0x265/0x8f0 init/main.c:1298
 do_initcall_level+0x157/0x207 init/main.c:1371
 do_initcalls+0x49/0x86 init/main.c:1387
 kernel_init_freeable+0x45c/0x60f init/main.c:1626
 kernel_init+0x19/0x290 init/main.c:1514
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Memory state around the buggy address:
 ffff88805b7b7700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88805b7b7780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88805b7b7800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88805b7b7880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88805b7b7900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2024/09/20 03:39 linux-6.1.y e526b12bf916 6f888b75 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: use-after-free Write in l2tp_session_delete
2024/08/29 01:01 linux-6.1.y ee5e09825b81 ef3de9e8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: use-after-free Write in l2tp_session_delete
* Struck through repros no longer work on HEAD.