==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff888129622000 by task syz.2.1406/5033
CPU: 1 PID: 5033 Comm: syz.2.1406 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
__dump_stack+0x21/0x30 lib/dump_stack.c:88
dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:427 [inline]
kasan_report+0x10f/0x150 mm/kasan/report.c:444
__asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:435
__sock_release net/socket.c:649 [inline]
sock_close+0xb8/0x200 net/socket.c:1336
__fput+0x22b/0x900 fs/file_table.c:311
____fput+0x15/0x20 fs/file_table.c:339
task_work_run+0x127/0x190 kernel/task_work.c:188
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop+0xd0/0xe0 kernel/entry/common.c:181
exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f1d4b718019
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:00007ffe2a6f08d8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f1d4b9a1da0 RCX: 00007f1d4b718019
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f1d4b9a1da0 R08: 00007f1d4b9a0038 R09: 0000000000000000
R10: 00000000003ffbc4 R11: 0000000000000246 R12: 0000000000038308
R13: 00007f1d4b9a018c R14: 00000000000380b0 R15: 00007f1d4b9a0180
Allocated by task 5034:
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:433 [inline]
____kasan_kmalloc mm/kasan/common.c:512 [inline]
__kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:521
kasan_kmalloc include/linux/kasan.h:227 [inline]
__kmalloc+0x13d/0x2c0 mm/slub.c:4436
kmalloc include/linux/slab.h:624 [inline]
kzalloc include/linux/slab.h:750 [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:1923 [inline]
__sys_connect+0x3cb/0x450 net/socket.c:1940
__do_sys_connect net/socket.c:1950 [inline]
__se_sys_connect net/socket.c:1947 [inline]
__x64_sys_connect+0x7a/0x90 net/socket.c:1947
x64_sys_call+0x7c/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
Freed by task 4529:
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:365
__kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
kasan_slab_free include/linux/kasan.h:193 [inline]
slab_free_hook mm/slub.c:1728 [inline]
slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1754
slab_free mm/slub.c:3526 [inline]
kfree+0xc4/0x270 mm/slub.c:4588
l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
l2tp_session_put+0xaf/0x1a0 net/l2tp/l2tp_core.c:193
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+0x6c8/0xbb0 kernel/workqueue.c:2328
worker_thread+0xaa0/0x1250 kernel/workqueue.c:2475
kthread+0x3f5/0x4f0 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
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
insert_work+0x51/0x310 kernel/workqueue.c:1373
__queue_work+0x8e1/0xc60 kernel/workqueue.c:1539
queue_work_on+0xde/0x150 kernel/workqueue.c:1566
queue_work include/linux/workqueue.h:510 [inline]
fqdir_exit+0xc8/0xe0 net/ipv4/inet_fragment.c:221
lowpan_frags_exit_net+0xa2/0xb0 net/ieee802154/6lowpan/reassembly.c:476
ops_exit_list net/core/net_namespace.c:172 [inline]
cleanup_net+0x58e/0xae0 net/core/net_namespace.c:599
process_one_work+0x6c8/0xbb0 kernel/workqueue.c:2328
worker_thread+0xaa0/0x1250 kernel/workqueue.c:2475
kthread+0x3f5/0x4f0 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
Second to 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
kvfree_call_rcu+0xb6/0x860 kernel/rcu/tree.c:3648
put_css_set_locked+0xa0a/0xa40 kernel/cgroup/cgroup.c:1016
cgroup_migrate_finish+0x155/0x300 kernel/cgroup/cgroup.c:2729
cgroup_attach_task+0x34c/0x520 kernel/cgroup/cgroup.c:2930
cgroup_attach_task_all+0xb4/0x140 kernel/cgroup/cgroup-v1.c:75
kvm_vm_worker_thread+0xcb/0x280 virt/kvm/kvm_main.c:5803
kthread+0x3f5/0x4f0 kernel/kthread.c:337
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
The buggy address belongs to the object at ffff888129622000
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
512-byte region [ffff888129622000, ffff888129622200)
The buggy address belongs to the page:
page:ffffea0004a58800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x129620
head:ffffea0004a58800 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 dead000000000100 dead000000000122 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 0x52a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 20, ts 19136292485, free_ts 0
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2607
prep_new_page+0x1c/0x110 mm/page_alloc.c:2613
get_page_from_freelist+0x2c3a/0x2cd0 mm/page_alloc.c:4487
__alloc_pages+0x1a2/0x460 mm/page_alloc.c:5824
alloc_slab_page mm/slub.c:-1 [inline]
allocate_slab mm/slub.c:1937 [inline]
new_slab+0xa0/0x4d0 mm/slub.c:2000
___slab_alloc+0x3ac/0x840 mm/slub.c:3033
__slab_alloc+0x49/0x90 mm/slub.c:3120
slab_alloc_node mm/slub.c:3211 [inline]
slab_alloc mm/slub.c:3255 [inline]
__kmalloc+0x16a/0x2c0 mm/slub.c:4432
kmalloc include/linux/slab.h:624 [inline]
kzalloc include/linux/slab.h:750 [inline]
neigh_alloc net/core/neighbour.c:438 [inline]
___neigh_create+0x6fb/0x1c50 net/core/neighbour.c:591
__neigh_create+0x31/0x40 net/core/neighbour.c:679
ip6_finish_output2+0xae3/0x1790 net/ipv6/ip6_output.c:127
__ip6_finish_output+0x621/0x7e0 net/ipv6/ip6_output.c:201
ip6_finish_output+0x31/0x220 net/ipv6/ip6_output.c:211
NF_HOOK_COND include/linux/netfilter.h:294 [inline]
ip6_output+0x1fa/0x410 net/ipv6/ip6_output.c:234
dst_output include/net/dst.h:453 [inline]
NF_HOOK include/linux/netfilter.h:305 [inline]
ndisc_send_skb+0x7f6/0xcf0 net/ipv6/ndisc.c:513
ndisc_send_rs+0x711/0x960 net/ipv6/ndisc.c:707
page_owner free stack trace missing
Memory state around the buggy address:
ffff888129621f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888129621f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888129622000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888129622080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888129622100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 5033 at net/l2tp/l2tp_ppp.c:156 pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Modules linked in:
CPU: 0 PID: 5033 Comm: syz.2.1406 Tainted: G B syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Code: 5d c3 e8 9c 83 0b fd be 02 00 00 00 eb 0a e8 90 83 0b fd be 01 00 00 00 4c 89 f7 e8 33 02 f2 fd e9 0f ff ff ff e8 79 83 0b fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 68 83 0b fd 4c 89 f7 be 03
RSP: 0018:ffffc90000c7fd10 EFLAGS: 00010293
RAX: ffffffff845e3367 RBX: ffff8881286c3000 RCX: ffff88811296cf00
RDX: 0000000000000000 RSI: 000000000cb0da20 RDI: 000000000c04eb7d
RBP: ffffc90000c7fd30 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff0e18e4c R12: dffffc0000000000
R13: dffffc0000000000 R14: 000000000cb0da20 R15: ffff888129622000
FS: 0000555586ed9500(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055ba74064300 CR3: 0000000124685000 CR4: 00000000003526b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:435
__sock_release net/socket.c:649 [inline]
sock_close+0xb8/0x200 net/socket.c:1336
__fput+0x22b/0x900 fs/file_table.c:311
____fput+0x15/0x20 fs/file_table.c:339
task_work_run+0x127/0x190 kernel/task_work.c:188
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop+0xd0/0xe0 kernel/entry/common.c:181
exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f1d4b718019
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:00007ffe2a6f08d8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f1d4b9a1da0 RCX: 00007f1d4b718019
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f1d4b9a1da0 R08: 00007f1d4b9a0038 R09: 0000000000000000
R10: 00000000003ffbc4 R11: 0000000000000246 R12: 0000000000038308
R13: 00007f1d4b9a018c R14: 00000000000380b0 R15: 00007f1d4b9a0180
---[ end trace 5640ae2004bd626f ]---