==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff88812afaa000 by task syz.6.4849/15461

CPU: 0 PID: 15461 Comm: syz.6.4849 Not tainted 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_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: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
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0xa7c/0x27c0 kernel/exit.c:886
 do_group_exit+0x21b/0x2e0 kernel/exit.c:1029
 get_signal+0x1382/0x14f0 kernel/signal.c:2891
 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
 ret_from_fork+0x15/0x30 arch/x86/entry/entry_64.S:288
RIP: 0033:0x7fae8879dc49
Code: Unable to access opcode bytes at 0x7fae8879dc1f.
RSP: 002b:00007fae871d61c0 EFLAGS: 00000202 ORIG_RAX: 00000000000001b3
RAX: 0000000000000000 RBX: 00007fae887591e0 RCX: 00007fae8879dc49
RDX: 00007fae887591e0 RSI: 0000000000000058 RDI: 00007fffa59326a0
RBP: 00007fae871d66c0 R08: 00007fae871d66c0 R09: 00007fffa5932787
R10: 0000000000000008 R11: 0000000000000202 R12: ffffffffffffffe8
R13: 000000000000006e R14: 00007fffa59326a0 R15: 00007fffa5932788
 </TASK>

Allocated by task 15455:
 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 15458:
 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

The buggy address belongs to the object at ffff88812afaa000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff88812afaa000, ffff88812afaa200)

The buggy address belongs to the physical page:
page:ffffea0004abea00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x12afa8
head:ffffea0004abea00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004b3fa00 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 92, tgid 92 (klogd), ts 426243068489, free_ts 425430239044
 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_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]
 alloc_skb_with_frags+0xa8/0x620 net/core/skbuff.c:6176
 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2761
 unix_dgram_sendmsg+0x5c1/0x1710 net/unix/af_unix.c:1947
 sock_sendmsg_nosec net/socket.c:716 [inline]
 __sock_sendmsg net/socket.c:728 [inline]
 __sys_sendto+0x4ac/0x660 net/socket.c:2142
 __do_sys_sendto net/socket.c:2154 [inline]
 __se_sys_sendto net/socket.c:2150 [inline]
 __x64_sys_sendto+0xe5/0x100 net/socket.c:2150
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1580 [inline]
 free_pcp_prepare mm/page_alloc.c:1654 [inline]
 free_unref_page_prepare+0x80c/0x820 mm/page_alloc.c:3621
 free_unref_page+0x93/0x530 mm/page_alloc.c:3719
 free_the_page mm/page_alloc.c:863 [inline]
 __free_pages+0x67/0x100 mm/page_alloc.c:6020
 __vunmap+0xa3c/0xc00 mm/vmalloc.c:2739
 __vfree mm/vmalloc.c:2788 [inline]
 vfree+0x61/0x90 mm/vmalloc.c:2819
 kcov_put kernel/kcov.c:437 [inline]
 kcov_close+0x2b/0x50 kernel/kcov.c:533
 __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+0xa7c/0x27c0 kernel/exit.c:886
 do_group_exit+0x21b/0x2e0 kernel/exit.c:1029
 __do_sys_exit_group kernel/exit.c:1040 [inline]
 __se_sys_exit_group kernel/exit.c:1038 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1038
 x64_sys_call+0x7b4/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:232
 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

Memory state around the buggy address:
 ffff88812afa9f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88812afa9f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88812afaa000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff88812afaa080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88812afaa100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 15461 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: 15461 Comm: syz.6.4849 Tainted: G    B              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:ffffc90000e57830 EFLAGS: 00010293

RAX: ffffffff849b9307 RBX: ffff88810ecbf000 RCX: ffff888111c62880
RDX: 0000000000000000 RSI: 000000001f3ff800 RDI: 000000000c04eb7d
RBP: ffffc90000e57850 R08: ffffffff87b747e7 R09: 1ffffffff0f6e8fc
R10: dffffc0000000000 R11: fffffbfff0f6e8fd R12: dffffc0000000000
R13: dffffc0000000000 R14: 000000001f3ff800 R15: ffff88812afaa000
FS:  0000000000000000(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555590eca948 CR3: 000000010d4f5000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000001800
DR3: 0000000000000000 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
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0xa7c/0x27c0 kernel/exit.c:886
 do_group_exit+0x21b/0x2e0 kernel/exit.c:1029
 get_signal+0x1382/0x14f0 kernel/signal.c:2891
 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
 ret_from_fork+0x15/0x30 arch/x86/entry/entry_64.S:288
RIP: 0033:0x7fae8879dc49
Code: Unable to access opcode bytes at 0x7fae8879dc1f.
RSP: 002b:00007fae871d61c0 EFLAGS: 00000202 ORIG_RAX: 00000000000001b3
RAX: 0000000000000000 RBX: 00007fae887591e0 RCX: 00007fae8879dc49
RDX: 00007fae887591e0 RSI: 0000000000000058 RDI: 00007fffa59326a0
RBP: 00007fae871d66c0 R08: 00007fae871d66c0 R09: 00007fffa5932787
R10: 0000000000000008 R11: 0000000000000202 R12: ffffffffffffffe8
R13: 000000000000006e R14: 00007fffa59326a0 R15: 00007fffa5932788
 </TASK>
---[ end trace 0000000000000000 ]---