==================================================================
BUG: KASAN: use-after-free in l2tp_xmit_core net/l2tp/l2tp_core.c:1031 [inline]
BUG: KASAN: use-after-free in l2tp_xmit_skb+0x4a/0x18e0 net/l2tp/l2tp_core.c:1132
Read of size 8 at addr ffff888131f3fc10 by task syz.8.7360/26613
CPU: 0 PID: 26613 Comm: syz.8.7360 Tainted: G W 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_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:351
l2tp_xmit_core net/l2tp/l2tp_core.c:1031 [inline]
l2tp_xmit_skb+0x4a/0x18e0 net/l2tp/l2tp_core.c:1132
pppol2tp_sendmsg+0x357/0x5d0 net/l2tp/l2tp_ppp.c:307
sock_sendmsg_nosec net/socket.c:716 [inline]
__sock_sendmsg net/socket.c:728 [inline]
____sys_sendmsg+0x5fb/0x9c0 net/socket.c:2508
___sys_sendmsg+0x2a2/0x360 net/socket.c:2562
__sys_sendmmsg+0x2cc/0x4e0 net/socket.c:2648
__do_sys_sendmmsg net/socket.c:2677 [inline]
__se_sys_sendmmsg net/socket.c:2674 [inline]
__x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2674
x64_sys_call+0x3f5/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:308
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
RIP: 0033:0x7f98fe59ce59
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:00007f98ff464028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f98fe815fa0 RCX: 00007f98fe59ce59
RDX: 0000000000034000 RSI: 0000200000004380 RDI: 0000000000000003
RBP: 00007f98fe632d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f98fe816038 R14: 00007f98fe815fa0 R15: 00007ffd8e6deb48
</TASK>
Allocated by task 26613:
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 26620:
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
Last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
__kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
kasan_record_aux_stack+0xe/0x10 mm/kasan/generic.c:491
task_work_add+0x7f/0x330 kernel/task_work.c:48
__io_req_task_work_add+0x356/0x8a0 io_uring/io_uring.c:1155
io_req_task_work_add io_uring/io_uring.h:87 [inline]
io_req_task_queue_fail io_uring/io_uring.c:1264 [inline]
io_wq_submit_work+0x471/0x810 io_uring/io_uring.c:-1
io_run_cancel io_uring/io-wq.c:893 [inline]
io_acct_cancel_pending_work+0x378/0x5f0 io_uring/io-wq.c:1059
io_wqe_enqueue+0x7d0/0x9a0 io_uring/io-wq.c:973
io_wq_enqueue+0x40/0x50 io_uring/io-wq.c:981
io_queue_iowq+0x314/0x4d0 io_uring/io_uring.c:445
io_queue_sqe_fallback+0xce/0x1b0 io_uring/io_uring.c:1959
io_submit_state_end io_uring/io_uring.c:2205 [inline]
io_submit_sqes+0x18eb/0x1ba0 io_uring/io_uring.c:2321
__do_sys_io_uring_enter io_uring/io_uring.c:3430 [inline]
__se_sys_io_uring_enter+0x32c/0x1f50 io_uring/io_uring.c:3362
__x64_sys_io_uring_enter+0xe5/0x100 io_uring/io_uring.c:3362
x64_sys_call+0x4b2/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:427
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
Second to last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
__kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
__call_rcu_common kernel/rcu/tree.c:2807 [inline]
call_rcu+0xcf/0xf50 kernel/rcu/tree.c:2926
fib6_info_release include/net/ip6_fib.h:350 [inline]
fib6_del_route net/ipv6/ip6_fib.c:2005 [inline]
fib6_del+0xbda/0xef0 net/ipv6/ip6_fib.c:2038
fib6_clean_node+0x2af/0x550 net/ipv6/ip6_fib.c:2200
fib6_walk_continue+0x55d/0x760 net/ipv6/ip6_fib.c:2122
fib6_walk+0x153/0x290 net/ipv6/ip6_fib.c:2170
fib6_clean_tree net/ipv6/ip6_fib.c:2250 [inline]
__fib6_clean_all net/ipv6/ip6_fib.c:2266 [inline]
fib6_clean_all+0x1a1/0x270 net/ipv6/ip6_fib.c:2277
rt6_sync_down_dev net/ipv6/route.c:4923 [inline]
rt6_disable_ip+0x123/0x8e0 net/ipv6/route.c:4928
addrconf_ifdown+0x15d/0x1950 net/ipv6/addrconf.c:3824
addrconf_notify+0x39f/0xe30 net/ipv6/addrconf.c:-1
notifier_call_chain kernel/notifier.c:87 [inline]
raw_notifier_call_chain+0xa1/0x110 kernel/notifier.c:455
call_netdevice_notifiers_info net/core/dev.c:2022 [inline]
call_netdevice_notifiers_extack net/core/dev.c:2060 [inline]
call_netdevice_notifiers net/core/dev.c:2074 [inline]
dev_close_many+0x325/0x4d0 net/core/dev.c:1622
unregister_netdevice_many+0x43f/0x1910 net/core/dev.c:10979
default_device_exit_batch+0x951/0x9f0 net/core/dev.c:11518
ops_exit_list net/core/net_namespace.c:177 [inline]
cleanup_net+0x630/0xb10 net/core/net_namespace.c:604
process_one_work+0x717/0xc30 kernel/workqueue.c:2302
worker_thread+0xa4d/0x11d0 kernel/workqueue.c:2449
kthread+0x281/0x320 kernel/kthread.c:386
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
The buggy address belongs to the object at ffff888131f3fc00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 16 bytes inside of
512-byte region [ffff888131f3fc00, ffff888131f3fe00)
The buggy address belongs to the physical page:
page:ffffea0004c7cf00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x131f3c
head:ffffea0004c7cf00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004ebd600 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 287, tgid 287 (syz-executor), ts 24788068672, 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+0xa4/0x1e0 mm/slab_common.c:951
kmalloc include/linux/slab.h:568 [inline]
kzalloc include/linux/slab.h:699 [inline]
new_dir fs/proc/proc_sysctl.c:973 [inline]
get_subdir fs/proc/proc_sysctl.c:1017 [inline]
__register_sysctl_table+0x947/0xe50 fs/proc/proc_sysctl.c:1379
register_net_sysctl+0x23f/0x250 net/sysctl_net.c:169
__addrconf_sysctl_register+0x277/0x3e0 net/ipv6/addrconf.c:7192
addrconf_sysctl_register+0x147/0x1a0 net/ipv6/addrconf.c:7239
ipv6_add_dev+0xbf5/0x1130 net/ipv6/addrconf.c:455
addrconf_notify+0x6d0/0xe30 net/ipv6/addrconf.c:3621
page_owner free stack trace missing
Memory state around the buggy address:
ffff888131f3fb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888131f3fb80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888131f3fc00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888131f3fc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888131f3fd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 26613 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: 26613 Comm: syz.8.7360 Tainted: G B W 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 3c c2 d5 fc be 02 00 00 00 eb 0a e8 30 c2 d5 fc be 01 00 00 00 4c 89 f7 e8 03 21 cd fd e9 0f ff ff ff e8 19 c2 d5 fc <0f> 0b 48 89 df e8 ff 00 00 00 eb bd e8 08 c2 d5 fc 4c 89 f7 be 03
RSP: 0018:ffffc90001dc7838 EFLAGS: 00010246
RAX: ffffffff849b9307 RBX: ffff888114c2f000 RCX: 0000000000080000
RDX: ffffc90002879000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffc90001dc7858 R08: ffff888114c2f083 R09: 1ffff11022985e10
R10: dffffc0000000000 R11: ffffed1022985e11 R12: dffffc0000000000
R13: 0000000000000000 R14: 000000001017b240 R15: ffff888131f3fc00
FS: 00007f98ff4646c0(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557595b908 CR3: 000000012af3e000 CR4: 00000000003506b0
DR0: 0000000000000008 DR1: 0000000000000002 DR2: 0000000000000404
DR3: ffffffffefffff14 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
pppol2tp_sendmsg+0xdf/0x5d0 net/l2tp/l2tp_ppp.c:270
sock_sendmsg_nosec net/socket.c:716 [inline]
__sock_sendmsg net/socket.c:728 [inline]
____sys_sendmsg+0x5fb/0x9c0 net/socket.c:2508
___sys_sendmsg+0x2a2/0x360 net/socket.c:2562
__sys_sendmmsg+0x2cc/0x4e0 net/socket.c:2648
__do_sys_sendmmsg net/socket.c:2677 [inline]
__se_sys_sendmmsg net/socket.c:2674 [inline]
__x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2674
x64_sys_call+0x3f5/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:308
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
RIP: 0033:0x7f98fe59ce59
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:00007f98ff464028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f98fe815fa0 RCX: 00007f98fe59ce59
RDX: 0000000000034000 RSI: 0000200000004380 RDI: 0000000000000003
RBP: 00007f98fe632d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f98fe816038 R14: 00007f98fe815fa0 R15: 00007ffd8e6deb48
</TASK>
---[ end trace 0000000000000000 ]---
------------[ cut here ]------------
WARNING: CPU: 0 PID: 26613 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: 26613 Comm: syz.8.7360 Tainted: G B W 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 3c c2 d5 fc be 02 00 00 00 eb 0a e8 30 c2 d5 fc be 01 00 00 00 4c 89 f7 e8 03 21 cd fd e9 0f ff ff ff e8 19 c2 d5 fc <0f> 0b 48 89 df e8 ff 00 00 00 eb bd e8 08 c2 d5 fc 4c 89 f7 be 03
RSP: 0018:ffffc90001dc7990 EFLAGS: 00010246
RAX: ffffffff849b9307 RBX: ffff888114c2f000 RCX: 0000000000080000
RDX: ffffc90002879000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffc90001dc79b0 R08: ffff888114c2f083 R09: 1ffff11022985e10
R10: dffffc0000000000 R11: ffffed1022985e11 R12: dffffc0000000000
R13: dffffc0000000000 R14: 000000001017b240 R15: ffff888131f3fc00
FS: 00007f98ff4646c0(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557595b908 CR3: 000000012af3e000 CR4: 00000000003506b0
DR0: 0000000000000008 DR1: 0000000000000002 DR2: 0000000000000404
DR3: ffffffffefffff14 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
get_signal+0x12b3/0x14f0 kernel/signal.c:2668
arch_do_signal_or_restart+0xd1/0x11c0 arch/x86/kernel/signal.c:871
exit_to_user_mode_loop+0x7a/0xb0 kernel/entry/common.c:174
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: 0033:0x7f98fe59ce59
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:00007f98ff464028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 00000000000002ba RBX: 00007f98fe815fa0 RCX: 00007f98fe59ce59
RDX: 0000000000034000 RSI: 0000200000004380 RDI: 0000000000000003
RBP: 00007f98fe632d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f98fe816038 R14: 00007f98fe815fa0 R15: 00007ffd8e6deb48
</TASK>
---[ end trace 0000000000000000 ]---