==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff88811d348000 by task syz.3.3556/12617
CPU: 1 PID: 12617 Comm: syz.3.3556 Tainted: G W 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
exit_task_work include/linux/task_work.h:33 [inline]
do_exit+0xb70/0x29a0 kernel/exit.c:890
do_group_exit+0x149/0x310 kernel/exit.c:1004
get_signal+0x64f/0x1430 kernel/signal.c:2908
arch_do_signal_or_restart+0xe2/0x1100 arch/x86/kernel/signal.c:867
handle_signal_work kernel/entry/common.c:154 [inline]
exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:178
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: 0033:0x7fd90df31019
Code: Unable to access opcode bytes at RIP 0x7fd90df30fef.
RSP: 002b:00007ffdf9917758 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffdfc RBX: 00000000000f95e7 RCX: 00007fd90df31019
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fd90e1b8fac
RBP: 0000000000000bea R08: 0017dad8a642be7e R09: 0000000000000000
R10: 00007ffdf9917860 R11: 0000000000000246 R12: 00007ffdf9917880
R13: 00007fd90e1b8fac R14: 00000000000fa1d1 R15: 00007ffdf9917860
Allocated by task 12619:
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 9364:
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
__call_rcu_common kernel/rcu/tree.c:3011 [inline]
call_rcu+0x10b/0xf60 kernel/rcu/tree.c:3129
fib6_info_release include/net/ip6_fib.h:349 [inline]
fib6_del_route net/ipv6/ip6_fib.c:1998 [inline]
fib6_del+0xbf0/0xf00 net/ipv6/ip6_fib.c:2031
fib6_clean_node+0x2a1/0x540 net/ipv6/ip6_fib.c:2193
fib6_walk_continue+0x54b/0x740 net/ipv6/ip6_fib.c:2115
fib6_walk+0x153/0x290 net/ipv6/ip6_fib.c:2163
fib6_clean_tree net/ipv6/ip6_fib.c:2243 [inline]
__fib6_clean_all net/ipv6/ip6_fib.c:2259 [inline]
fib6_clean_all+0x1a1/0x270 net/ipv6/ip6_fib.c:2270
rt6_sync_down_dev net/ipv6/route.c:4906 [inline]
rt6_disable_ip+0x115/0x730 net/ipv6/route.c:4911
addrconf_ifdown+0x144/0x1910 net/ipv6/addrconf.c:3802
addrconf_notify+0x3bd/0xe00 net/ipv6/addrconf.c:-1
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:391
call_netdevice_notifiers_info net/core/dev.c:2070 [inline]
call_netdevice_notifiers_extack net/core/dev.c:2082 [inline]
call_netdevice_notifiers net/core/dev.c:2096 [inline]
dev_close_many+0x325/0x4d0 net/core/dev.c:1671
unregister_netdevice_many+0x477/0x1a00 net/core/dev.c:11152
default_device_exit_batch+0x35e/0x3c0 net/core/dev.c:11709
ops_exit_list net/core/net_namespace.c:177 [inline]
cleanup_net+0x605/0xae0 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
The buggy address belongs to the object at ffff88811d348000
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
512-byte region [ffff88811d348000, ffff88811d348200)
The buggy address belongs to the page:
page:ffffea000474d200 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88811d34b800 pfn:0x11d348
head:ffffea000474d200 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004a5c708 ffffea0004604308 ffff888100042f00
raw: ffff88811d34b800 000000000010000f 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 4589, ts 725863893254, free_ts 725594954824
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_track_caller+0x169/0x2c0 mm/slub.c:4954
kmalloc_reserve net/core/skbuff.c:357 [inline]
__alloc_skb+0x210/0x730 net/core/skbuff.c:428
alloc_skb include/linux/skbuff.h:1183 [inline]
alloc_skb_with_frags+0xa8/0x620 net/core/skbuff.c:6207
sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2542
unix_dgram_sendmsg+0x6f3/0x19b0 net/unix/af_unix.c:1816
sock_sendmsg_nosec net/socket.c:704 [inline]
__sock_sendmsg net/socket.c:716 [inline]
sock_write_iter+0x2a6/0x3a0 net/socket.c:1080
call_write_iter include/linux/fs.h:2212 [inline]
new_sync_write fs/read_write.c:507 [inline]
vfs_write+0x831/0xfd0 fs/read_write.c:594
ksys_write+0x14a/0x260 fs/read_write.c:647
__do_sys_write fs/read_write.c:659 [inline]
__se_sys_write fs/read_write.c:656 [inline]
__x64_sys_write+0x7b/0x90 fs/read_write.c:656
page last free stack trace:
reset_page_owner include/linux/page_owner.h:26 [inline]
free_pages_prepare mm/page_alloc.c:1474 [inline]
free_pcp_prepare mm/page_alloc.c:1546 [inline]
free_unref_page_prepare+0x5fa/0x600 mm/page_alloc.c:3536
free_unref_page+0xae/0x540 mm/page_alloc.c:3618
free_the_page mm/page_alloc.c:805 [inline]
__free_pages+0x6c/0x100 mm/page_alloc.c:5900
free_nonslab_page+0x86/0xc0 mm/slub.c:3564
kfree+0x19a/0x270 mm/slub.c:4585
destroy_discard_cmd_control fs/f2fs/segment.c:2153 [inline]
f2fs_destroy_segment_manager+0x1b2/0xd80 fs/f2fs/segment.c:5393
f2fs_put_super+0x6b3/0xbd0 fs/f2fs/super.c:1704
generic_shutdown_super+0x151/0x330 fs/super.c:475
kill_block_super+0x7f/0xf0 fs/super.c:1427
kill_f2fs_super+0x30a/0x3d0 fs/f2fs/super.c:4745
deactivate_locked_super+0xa0/0x100 fs/super.c:335
deactivate_super+0xaf/0xe0 fs/super.c:366
cleanup_mnt+0x44f/0x500 fs/namespace.c:1149
__cleanup_mnt+0x19/0x20 fs/namespace.c:1156
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
Memory state around the buggy address:
ffff88811d347f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88811d347f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88811d348000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88811d348080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88811d348100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 1 PID: 12617 at net/l2tp/l2tp_ppp.c:156 pppol2tp_sock_to_session+0x167/0x1b0 net/l2tp/l2tp_ppp.c:156
Modules linked in:
CPU: 1 PID: 12617 Comm: syz.3.3556 Tainted: G B W 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:ffffc90001377890 EFLAGS: 00010293
RAX: ffffffff845e3367 RBX: ffff8881130d0000 RCX: ffff8881169a62c0
RDX: 0000000000000000 RSI: 000000000aaa93e0 RDI: 000000000c04eb7d
RBP: ffffc900013778b0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff0e18e4c R12: dffffc0000000000
R13: dffffc0000000000 R14: 000000000aaa93e0 R15: ffff88811d348000
FS: 0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055556092f908 CR3: 000000010b040000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
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
exit_task_work include/linux/task_work.h:33 [inline]
do_exit+0xb70/0x29a0 kernel/exit.c:890
do_group_exit+0x149/0x310 kernel/exit.c:1004
get_signal+0x64f/0x1430 kernel/signal.c:2908
arch_do_signal_or_restart+0xe2/0x1100 arch/x86/kernel/signal.c:867
handle_signal_work kernel/entry/common.c:154 [inline]
exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:178
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: 0033:0x7fd90df31019
Code: Unable to access opcode bytes at RIP 0x7fd90df30fef.
RSP: 002b:00007ffdf9917758 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffdfc RBX: 00000000000f95e7 RCX: 00007fd90df31019
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fd90e1b8fac
RBP: 0000000000000bea R08: 0017dad8a642be7e R09: 0000000000000000
R10: 00007ffdf9917860 R11: 0000000000000246 R12: 00007ffdf9917880
R13: 00007fd90e1b8fac R14: 00000000000fa1d1 R15: 00007ffdf9917860
---[ end trace fcec59007ec42c1e ]---