==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff888130c54c00 by task syz.4.244/1046
CPU: 1 PID: 1046 Comm: syz.4.244 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
__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_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:350
pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:434
__sock_release net/socket.c:652 [inline]
sock_close+0xc9/0x220 net/socket.c:1390
__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
exit_task_work include/linux/task_work.h:39 [inline]
do_exit+0xb0d/0x29f0 kernel/exit.c:896
__do_sys_exit kernel/exit.c:1006 [inline]
__se_sys_exit kernel/exit.c:1004 [inline]
__x64_sys_exit+0x40/0x40 kernel/exit.c:1004
x64_sys_call+0x67/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:61
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: 0033:0x7f0bfef9e559
Code: Unable to access opcode bytes at 0x7f0bfef9e52f.
RSP: 002b:00007f0bffeddef8 EFLAGS: 00000246 ORIG_RAX: 000000000000003c
RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f0bfef9e559
RDX: 00007f0bffede9c8 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f0bff0358b0 R08: 0000000000000000 R09: 0000000000000058
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0bff226038 R14: 00007f0bff225fa0 R15: 00007fffe89bd728
Allocated by task 1045:
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:1614
pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:771
__sys_connect_file net/socket.c:2001 [inline]
__sys_connect+0x3da/0x460 net/socket.c:2018
__do_sys_connect net/socket.c:2028 [inline]
__se_sys_connect net/socket.c:2025 [inline]
__x64_sys_connect+0x7a/0x90 net/socket.c:2025
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 536:
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
l2tp_session_delete+0x3df/0x4d0 net/l2tp/l2tp_core.c:1587
l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1233 [inline]
l2tp_tunnel_del_work+0x199/0x410 net/l2tp/l2tp_core.c:1271
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 ffff888130c54c00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
512-byte region [ffff888130c54c00, ffff888130c54e00)
The buggy address belongs to the physical page:
page:ffffea0004c31500 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x130c54
head:ffffea0004c31500 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004c31300 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 18755032429, free_ts 18752157545
set_page_owner include/linux/page_owner.h:33 [inline]
post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2673
prep_new_page+0x1c/0x110 mm/page_alloc.c:2680
get_page_from_freelist+0x2ca9/0x2d20 mm/page_alloc.c:4587
__alloc_pages+0x1fa/0x610 mm/page_alloc.c:5931
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_node_track_caller+0xa1/0x1e0 mm/slab_common.c:958
kmalloc_reserve net/core/skbuff.c:449 [inline]
__alloc_skb+0x226/0x4a0 net/core/skbuff.c:518
alloc_skb include/linux/skbuff.h:1322 [inline]
nlmsg_new include/net/netlink.h:987 [inline]
inet_netconf_notify_devconf+0x169/0x220 net/ipv4/devinet.c:2128
__devinet_sysctl_register+0x2af/0x320 net/ipv4/devinet.c:2618
devinet_sysctl_register+0x169/0x1e0 net/ipv4/devinet.c:2652
inetdev_init+0x2ca/0x510 net/ipv4/devinet.c:280
inetdev_event+0x1f4/0x10a0 net/ipv4/devinet.c:1547
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1581 [inline]
free_pcp_prepare mm/page_alloc.c:1655 [inline]
free_unref_page_prepare+0x81b/0x820 mm/page_alloc.c:3622
free_unref_page+0x93/0x530 mm/page_alloc.c:3720
free_the_page mm/page_alloc.c:863 [inline]
__free_pages+0x67/0x100 mm/page_alloc.c:6021
free_pages+0x82/0x90 mm/page_alloc.c:6032
__stack_depot_save+0x45f/0x490 lib/stackdepot.c:506
stack_depot_save+0x13/0x20 lib/stackdepot.c:533
ref_tracker_alloc+0x1bf/0x4a0 lib/ref_tracker.c:92
__netdev_tracker_alloc include/linux/netdevice.h:4085 [inline]
netdev_hold include/linux/netdevice.h:4114 [inline]
rx_queue_add_kobject net/core/net-sysfs.c:1054 [inline]
net_rx_queue_update_kobjects+0x147/0x470 net/core/net-sysfs.c:1108
register_queue_kobjects net/core/net-sysfs.c:1768 [inline]
netdev_register_kobject+0x23d/0x330 net/core/net-sysfs.c:2013
register_netdevice+0xec9/0x1550 net/core/dev.c:10206
rtnl_newlink_create net/core/rtnetlink.c:3428 [inline]
__rtnl_newlink net/core/rtnetlink.c:3646 [inline]
rtnl_newlink+0x1660/0x20d0 net/core/rtnetlink.c:3659
rtnetlink_rcv_msg+0xb28/0xde0 net/core/rtnetlink.c:6154
netlink_rcv_skb+0x200/0x450 net/netlink/af_netlink.c:2526
rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:6172
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x8c1/0xa60 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b9/0xbd0 net/netlink/af_netlink.c:1878
Memory state around the buggy address:
ffff888130c54b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888130c54b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888130c54c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888130c54c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888130c54d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1046 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: 1046 Comm: syz.4.244 Tainted: G B syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
RIP: 0010:pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Code: 5d c3 e8 7c 2a d5 fc be 02 00 00 00 eb 0a e8 70 2a d5 fc be 01 00 00 00 4c 89 f7 e8 63 fb cc fd e9 0f ff ff ff e8 59 2a d5 fc <0f> 0b 48 89 df e8 ff 00 00 00 eb bd e8 48 2a d5 fc 4c 89 f7 be 03
RSP: 0018:ffffc900010e7b90 EFLAGS: 00010293
RAX: ffffffff849c43e7 RBX: ffff88810e349000 RCX: ffff88810d816540
RDX: 0000000000000000 RSI: 00000000182b4500 RDI: 000000000c04eb7d
RBP: ffffc900010e7bb0 R08: ffffffff87b777e7 R09: 1ffffffff0f6eefc
R10: dffffc0000000000 R11: fffffbfff0f6eefd R12: dffffc0000000000
R13: dffffc0000000000 R14: 00000000182b4500 R15: ffff888130c54c00
FS: 0000000000000000(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f25ae8a0bd0 CR3: 000000000700f000 CR4: 00000000003526b0
Call Trace:
pppol2tp_release+0x150/0x2b0 net/l2tp/l2tp_ppp.c:434
__sock_release net/socket.c:652 [inline]
sock_close+0xc9/0x220 net/socket.c:1390
__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
exit_task_work include/linux/task_work.h:39 [inline]
do_exit+0xb0d/0x29f0 kernel/exit.c:896
__do_sys_exit kernel/exit.c:1006 [inline]
__se_sys_exit kernel/exit.c:1004 [inline]
__x64_sys_exit+0x40/0x40 kernel/exit.c:1004
x64_sys_call+0x67/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:61
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: 0033:0x7f0bfef9e559
Code: Unable to access opcode bytes at 0x7f0bfef9e52f.
RSP: 002b:00007f0bffeddef8 EFLAGS: 00000246 ORIG_RAX: 000000000000003c
RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f0bfef9e559
RDX: 00007f0bffede9c8 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f0bff0358b0 R08: 0000000000000000 R09: 0000000000000058
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0bff226038 R14: 00007f0bff225fa0 R15: 00007fffe89bd728
---[ end trace 0000000000000000 ]---