==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff8881162a4000 by task syz.2.5684/16137
CPU: 0 PID: 16137 Comm: syz.2.5684 Tainted: G W syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
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:184
exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:217
__syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:310
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fc323208159
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:00007ffdcd668518 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007ffdcd668600 RCX: 00007fc323208159
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00000000000ab08b R08: 0000000000000001 R09: 0000000000000000
R10: 0000001b33d20000 R11: 0000000000000246 R12: 00007ffdcd668640
R13: 00007fc32348ffac R14: 00000000000ab6e5 R15: 00007fc32348ffa0
Allocated by task 16138:
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 8252:
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
The buggy address belongs to the object at ffff8881162a4000
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
512-byte region [ffff8881162a4000, ffff8881162a4200)
The buggy address belongs to the page:
page:ffffea000458a900 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1162a4
head:ffffea000458a900 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004686e00 0000000400000004 ffff888100042f00
raw: 0000000000000000 0000000080100010 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 14548, ts 635231285316, free_ts 607181207359
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]
fib6_info_alloc+0x34/0xe0 net/ipv6/ip6_fib.c:155
ip6_route_info_create+0x51b/0x14d0 net/ipv6/route.c:3783
ip6_route_add+0x27/0x130 net/ipv6/route.c:3879
addrconf_prefix_route+0x233/0x310 net/ipv6/addrconf.c:2478
inet6_addr_add+0x50b/0x9d0 net/ipv6/addrconf.c:3035
inet6_rtm_newaddr+0x6e7/0x9c0 net/ipv6/addrconf.c:4985
rtnetlink_rcv_msg+0x9fd/0xcb0 net/core/rtnetlink.c:5662
netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2520
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_slab+0xe5/0x1e0 mm/slub.c:2025
free_slab mm/slub.c:2040 [inline]
discard_slab mm/slub.c:2046 [inline]
__unfreeze_partials+0x15a/0x190 mm/slub.c:2532
put_cpu_partial+0xc6/0x120 mm/slub.c:2612
__slab_free+0x1d4/0x290 mm/slub.c:3395
do_slab_free mm/slub.c:3514 [inline]
___cache_free+0x104/0x120 mm/slub.c:3535
qlink_free+0x4d/0x90 mm/kasan/quarantine.c:157
qlist_free_all+0x5f/0xb0 mm/kasan/quarantine.c:176
kasan_quarantine_reduce+0x14a/0x170 mm/kasan/quarantine.c:283
__kasan_slab_alloc+0x2f/0xe0 mm/kasan/common.c:443
kasan_slab_alloc include/linux/kasan.h:217 [inline]
slab_post_alloc_hook+0x4f/0x2b0 mm/slab.h:550
slab_alloc_node mm/slub.c:3245 [inline]
slab_alloc mm/slub.c:3255 [inline]
kmem_cache_alloc+0xf7/0x260 mm/slub.c:3260
kmem_cache_alloc_node include/linux/slab.h:492 [inline]
__alloc_skb+0xe4/0x730 net/core/skbuff.c:416
alloc_skb_fclone include/linux/skbuff.h:1233 [inline]
sk_stream_alloc_skb+0x216/0xb70 net/ipv4/tcp.c:892
Memory state around the buggy address:
ffff8881162a3f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8881162a3f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8881162a4000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8881162a4080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8881162a4100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 16137 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: 16137 Comm: syz.2.5684 Tainted: G B W 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 3c ac 0a fd be 02 00 00 00 eb 0a e8 30 ac 0a fd be 01 00 00 00 4c 89 f7 e8 73 2e f1 fd e9 0f ff ff ff e8 19 ac 0a fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 08 ac 0a fd 4c 89 f7 be 03
RSP: 0018:ffffc90000fe7d10 EFLAGS: 00010293
RAX: ffffffff845f2f47 RBX: ffff888121758000 RCX: ffff88811ea13c00
RDX: 0000000000000000 RSI: 000000003b1d5a80 RDI: 000000000c04eb7d
RBP: ffffc90000fe7d30 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff0e1904c R12: dffffc0000000000
R13: dffffc0000000000 R14: 000000003b1d5a80 R15: ffff8881162a4000
FS: 000055558b144500(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6474f722f8 CR3: 000000011c66c000 CR4: 00000000003506b0
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:184
exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:217
__syscall_exit_to_user_mode_work kernel/entry/common.c:299 [inline]
syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:310
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fc323208159
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:00007ffdcd668518 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007ffdcd668600 RCX: 00007fc323208159
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00000000000ab08b R08: 0000000000000001 R09: 0000000000000000
R10: 0000001b33d20000 R11: 0000000000000246 R12: 00007ffdcd668640
R13: 00007fc32348ffac R14: 00000000000ab6e5 R15: 00007fc32348ffa0
---[ end trace a3bf61926aedcea0 ]---