==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff88811812dc00 by task syz.4.1232/4543
CPU: 1 PID: 4543 Comm: syz.4.1232 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
exit_task_work include/linux/task_work.h:33 [inline]
do_exit+0xb70/0x29a0 kernel/exit.c:890
__do_sys_exit kernel/exit.c:973 [inline]
__se_sys_exit kernel/exit.c:971 [inline]
__x64_sys_exit+0x40/0x40 kernel/exit.c:971
x64_sys_call+0x44/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:61
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
RIP: 0033:0x7ff60d0c90d9
Code: Unable to access opcode bytes at RIP 0x7ff60d0c90af.
RSP: 002b:00007ff60bb21ef8 EFLAGS: 00000246 ORIG_RAX: 000000000000003c
RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007ff60d0c90d9
RDX: 00007ff60bb229c8 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007ff60d160024 R08: 0000000000000000 R09: 0000000000000058
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff60d351038 R14: 00007ff60d350fa0 R15: 00007ffe815d4308
Allocated by task 4541:
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 315:
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 ffff88811812dc00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
512-byte region [ffff88811812dc00, ffff88811812de00)
The buggy address belongs to the page:
page:ffffea0004604b00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11812c
head:ffffea0004604b00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 0000000000000000 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 4536, ts 249622819544, free_ts 243149243107
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
unix_seqpacket_sendmsg+0x118/0x1e0 net/unix/af_unix.c:2277
sock_sendmsg_nosec net/socket.c:704 [inline]
__sock_sendmsg net/socket.c:716 [inline]
____sys_sendmsg+0x5be/0x8f0 net/socket.c:2436
___sys_sendmsg+0x236/0x2e0 net/socket.c:2490
__sys_sendmsg net/socket.c:2519 [inline]
__do_sys_sendmsg net/socket.c:2528 [inline]
__se_sys_sendmsg net/socket.c:2526 [inline]
__x64_sys_sendmsg+0x201/0x2d0 net/socket.c:2526
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
__vunmap+0x801/0x980 mm/vmalloc.c:2660
__vfree mm/vmalloc.c:2709 [inline]
vfree+0x8b/0xc0 mm/vmalloc.c:2740
kcov_mmap+0x8f/0x130 kernel/kcov.c:498
call_mmap include/linux/fs.h:2217 [inline]
mmap_file+0x60/0xb0 mm/util.c:1099
__mmap_region mm/mmap.c:1808 [inline]
mmap_region+0xe42/0x1700 mm/mmap.c:2959
do_mmap+0x812/0xf10 mm/mmap.c:1598
vm_mmap_pgoff+0x1d6/0x410 mm/util.c:555
ksys_mmap_pgoff+0x161/0x1d0 mm/mmap.c:1647
__do_sys_mmap arch/x86/kernel/sys_x86_64.c:93 [inline]
__se_sys_mmap arch/x86/kernel/sys_x86_64.c:86 [inline]
__x64_sys_mmap+0xfa/0x110 arch/x86/kernel/sys_x86_64.c:86
x64_sys_call+0x83/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:10
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
Memory state around the buggy address:
ffff88811812db00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88811812db80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88811812dc00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88811812dc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88811812dd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 1 PID: 4543 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: 4543 Comm: syz.4.1232 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 2c 83 0b fd be 02 00 00 00 eb 0a e8 20 83 0b fd be 01 00 00 00 4c 89 f7 e8 33 02 f2 fd e9 0f ff ff ff e8 09 83 0b fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 f8 82 0b fd 4c 89 f7 be 03
RSP: 0018:ffffc90001acfbf0 EFLAGS: 00010293
RAX: ffffffff845e33d7 RBX: ffff888133c63000 RCX: ffff8881192462c0
RDX: 0000000000000000 RSI: 000000000cb02e80 RDI: 000000000c04eb7d
RBP: ffffc90001acfc10 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff0e18e4c R12: dffffc0000000000
R13: dffffc0000000000 R14: 000000000cb02e80 R15: ffff88811812dc00
FS: 0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8e4ca28d0c CR3: 000000011d94d000 CR4: 00000000003526a0
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
exit_task_work include/linux/task_work.h:33 [inline]
do_exit+0xb70/0x29a0 kernel/exit.c:890
__do_sys_exit kernel/exit.c:973 [inline]
__se_sys_exit kernel/exit.c:971 [inline]
__x64_sys_exit+0x40/0x40 kernel/exit.c:971
x64_sys_call+0x44/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:61
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
RIP: 0033:0x7ff60d0c90d9
Code: Unable to access opcode bytes at RIP 0x7ff60d0c90af.
RSP: 002b:00007ff60bb21ef8 EFLAGS: 00000246 ORIG_RAX: 000000000000003c
RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007ff60d0c90d9
RDX: 00007ff60bb229c8 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007ff60d160024 R08: 0000000000000000 R09: 0000000000000058
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff60d351038 R14: 00007ff60d350fa0 R15: 00007ffe815d4308
---[ end trace cd0b48c071819227 ]---