==================================================================
BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156
Read of size 4 at addr ffff8881225a3c00 by task syz.7.2600/9022

CPU: 1 PID: 9022 Comm: syz.7.2600 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 __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_sendmsg+0xdf/0x5f0 net/l2tp/l2tp_ppp.c:271
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 __sys_sendto+0x46d/0x620 net/socket.c:2063
 __do_sys_sendto net/socket.c:2075 [inline]
 __se_sys_sendto net/socket.c:2071 [inline]
 __x64_sys_sendto+0xe5/0x100 net/socket.c:2071
 x64_sys_call+0x178/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:45
 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: 0033:0x7fcf685a790e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007fcf6701de88 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007fcf6701f6c0 RCX: 00007fcf685a790e
RDX: 0000000000000020 RSI: 00007fcf6701e000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007fcf6701df04 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 00007fcf6701df58 R14: 00007fcf6701e000 R15: 0000000000000000
 </TASK>

Allocated by task 9021:
 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 9021:
 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
 pppol2tp_ioctl+0x748/0x960 net/l2tp/l2tp_ppp.c:-1
 pppox_ioctl+0x1e4/0x320 drivers/net/ppp/pppox.c:93
 sock_do_ioctl+0x103/0x310 net/socket.c:1138
 sock_ioctl+0x459/0x6d0 net/socket.c:1257
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0x121/0x1a0 fs/ioctl.c:860
 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:860
 x64_sys_call+0x2f/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:17
 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

The buggy address belongs to the object at ffff8881225a3c00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8881225a3c00, ffff8881225a3e00)
The buggy address belongs to the page:
page:ffffea0004896800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1225a0
head:ffffea0004896800 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 dead000000000100 dead000000000122 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 0x152a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_HARDWALL), pid 0, ts 145896746198, free_ts 140531261137
 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]
 neigh_alloc net/core/neighbour.c:438 [inline]
 ___neigh_create+0x6fb/0x1c50 net/core/neighbour.c:591
 __neigh_create+0x31/0x40 net/core/neighbour.c:679
 ip_neigh_gw4+0x23f/0x300 include/net/route.h:373
 ip_neigh_for_gw include/net/route.h:391 [inline]
 ip_finish_output2+0xc61/0xec0 net/ipv4/ip_output.c:222
 __ip_finish_output+0x161/0x360 net/ipv4/ip_output.c:-1
 ip_finish_output+0x31/0x220 net/ipv4/ip_output.c:316
 NF_HOOK_COND include/linux/netfilter.h:294 [inline]
 ip_output+0x1ea/0x390 net/ipv4/ip_output.c:434
 dst_output include/net/dst.h:453 [inline]
 ip_local_out+0x96/0xb0 net/ipv4/ip_output.c:126
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+0x29/0x40 mm/slub.c:2046
 __slab_free+0x211/0x290 mm/slub.c:3431
 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_trace+0xfb/0x270 mm/slub.c:3272
 kmalloc include/linux/slab.h:619 [inline]
 dummy_urb_enqueue+0x7d/0x710 drivers/usb/gadget/udc/dummy_hcd.c:1274
 usb_hcd_submit_urb+0x317/0x17a0 drivers/usb/core/hcd.c:1557
 usb_submit_urb+0x1091/0x1730 drivers/usb/core/urb.c:594

Memory state around the buggy address:
 ffff8881225a3b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8881225a3b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8881225a3c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8881225a3c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881225a3d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 9022 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: 9022 Comm: syz.7.2600 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 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:ffffc90001b57c38 EFLAGS: 00010293
RAX: ffffffff845e33d7 RBX: ffff888136a14000 RCX: ffff8881195d4f00
RDX: 0000000000000000 RSI: 0000000044d4d500 RDI: 000000000c04eb7d
RBP: ffffc90001b57c58 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff0e18e4c R12: dffffc0000000000
R13: 0000000000000020 R14: 0000000044d4d500 R15: ffff8881225a3c00
FS:  00007fcf6701f6c0(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c2f8e91 CR3: 00000001622b8000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 pppol2tp_sendmsg+0xdf/0x5f0 net/l2tp/l2tp_ppp.c:271
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 __sys_sendto+0x46d/0x620 net/socket.c:2063
 __do_sys_sendto net/socket.c:2075 [inline]
 __se_sys_sendto net/socket.c:2071 [inline]
 __x64_sys_sendto+0xe5/0x100 net/socket.c:2071
 x64_sys_call+0x178/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:45
 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: 0033:0x7fcf685a790e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007fcf6701de88 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007fcf6701f6c0 RCX: 00007fcf685a790e
RDX: 0000000000000020 RSI: 00007fcf6701e000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007fcf6701df04 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 00007fcf6701df58 R14: 00007fcf6701e000 R15: 0000000000000000
 </TASK>
---[ end trace 02b7afc408bb2ea0 ]---
------------[ cut here ]------------
WARNING: CPU: 0 PID: 9022 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: 9022 Comm: syz.7.2600 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 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:ffffc90001b57a48 EFLAGS: 00010293
RAX: ffffffff845e33d7 RBX: ffff888136a14000 RCX: ffff8881195d4f00
RDX: 0000000000000000 RSI: 0000000044d4d500 RDI: 000000000c04eb7d
RBP: ffffc90001b57a68 R08: ffff888136a14083 R09: 1ffff11026d42810
R10: dffffc0000000000 R11: ffffed1026d42811 R12: dffffc0000000000
R13: dffffc0000000000 R14: 0000000044d4d500 R15: ffff8881225a3c00
FS:  00007fcf6701f6c0(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fec374dd2f8 CR3: 00000001622b8000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 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
 get_signal+0x13b1/0x1430 kernel/signal.c:2680
 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: 0033:0x7fcf685a790e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007fcf6701de88 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: fffffffffffffff7 RBX: 00007fcf6701f6c0 RCX: 00007fcf685a790e
RDX: 0000000000000020 RSI: 00007fcf6701e000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007fcf6701df04 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 00007fcf6701df58 R14: 00007fcf6701e000 R15: 0000000000000000
 </TASK>
---[ end trace 02b7afc408bb2ea1 ]---