================================================================== BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:840 [inline] BUG: KASAN: use-after-free in hlist_del_init include/linux/list.h:866 [inline] BUG: KASAN: use-after-free in l2tp_session_unhash net/l2tp/l2tp_core.c:1202 [inline] BUG: KASAN: use-after-free in l2tp_session_delete+0x133/0x4a0 net/l2tp/l2tp_core.c:1584 Write of size 8 at addr ffff88811d602c80 by task syz.3.81/657 CPU: 0 PID: 657 Comm: syz.3.81 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026 Call Trace: __dump_stack+0x21/0x24 lib/dump_stack.c:77 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248 __kasan_report mm/kasan/report.c:435 [inline] kasan_report+0x100/0x140 mm/kasan/report.c:452 __asan_report_store8_noabort+0x17/0x20 mm/kasan/report_generic.c:314 __hlist_del include/linux/list.h:840 [inline] hlist_del_init include/linux/list.h:866 [inline] l2tp_session_unhash net/l2tp/l2tp_core.c:1202 [inline] l2tp_session_delete+0x133/0x4a0 net/l2tp/l2tp_core.c:1584 pppol2tp_release+0x169/0x2b0 net/l2tp/l2tp_ppp.c:439 __sock_release net/socket.c:597 [inline] sock_close+0xb8/0x200 net/socket.c:1286 __fput+0x2dc/0x730 fs/file_table.c:281 ____fput+0x15/0x20 fs/file_table.c:314 task_work_run+0x127/0x190 kernel/task_work.c:189 tracehook_notify_resume include/linux/tracehook.h:188 [inline] exit_to_user_mode_loop+0xcb/0xe0 kernel/entry/common.c:172 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:199 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:274 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f18a5c0de59 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:00007ffd7e986118 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 00007f18a5e88da0 RCX: 00007f18a5c0de59 RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003 RBP: 00007f18a5e88da0 R08: 0000000000000006 R09: 0000000000000000 R10: 000000000003fd64 R11: 0000000000000246 R12: 0000000000009f86 R13: 00007f18a5e8709c R14: 0000000000009d38 R15: 00007f18a5e87090 Allocated by task 658: 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:430 [inline] ____kasan_kmalloc mm/kasan/common.c:509 [inline] __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:518 kasan_kmalloc include/linux/kasan.h:254 [inline] __kmalloc+0x19f/0x330 mm/slub.c:4038 kmalloc include/linux/slab.h:560 [inline] kzalloc include/linux/slab.h:667 [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:1866 [inline] __sys_connect+0x3ce/0x450 net/socket.c:1883 __do_sys_connect net/socket.c:1893 [inline] __se_sys_connect net/socket.c:1890 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:1890 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb Freed by task 659: 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:362 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370 kasan_slab_free include/linux/kasan.h:220 [inline] slab_free_hook mm/slub.c:1600 [inline] slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626 slab_free mm/slub.c:3208 [inline] kfree+0xc0/0x270 mm/slub.c:4196 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline] l2tp_session_put+0xb2/0x1a0 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+0xda/0x380 net/socket.c:1067 sock_ioctl+0x472/0x740 net/socket.c:1207 vfs_ioctl fs/ioctl.c:48 [inline] __do_sys_ioctl fs/ioctl.c:753 [inline] __se_sys_ioctl+0x121/0x1a0 fs/ioctl.c:739 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:739 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb The buggy address belongs to the object at ffff88811d602c00 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 128 bytes inside of 512-byte region [ffff88811d602c00, ffff88811d602e00) The buggy address belongs to the page: page:ffffea0004758000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11d600 head:ffffea0004758000 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 ffffea0004741700 0000000700000007 ffff888100043080 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 134, ts 16191413700, free_ts 16191296086 set_page_owner include/linux/page_owner.h:35 [inline] post_alloc_hook mm/page_alloc.c:2456 [inline] prep_new_page+0x176/0x190 mm/page_alloc.c:2462 get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254 __alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384 alloc_slab_page mm/slub.c:-1 [inline] allocate_slab mm/slub.c:1813 [inline] new_slab+0x84/0x3f0 mm/slub.c:1874 new_slab_objects mm/slub.c:2632 [inline] ___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796 __slab_alloc+0x63/0xa0 mm/slub.c:2836 slab_alloc_node mm/slub.c:2918 [inline] slab_alloc mm/slub.c:2960 [inline] __kmalloc_track_caller+0x1e4/0x310 mm/slub.c:4541 __kmalloc_reserve net/core/skbuff.c:144 [inline] __alloc_skb+0xdc/0x520 net/core/skbuff.c:212 alloc_skb include/linux/skbuff.h:1126 [inline] alloc_skb_with_frags+0xa3/0x560 net/core/skbuff.c:6006 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2393 unix_dgram_sendmsg+0x6f3/0x18f0 net/unix/af_unix.c:1725 sock_sendmsg_nosec net/socket.c:652 [inline] __sock_sendmsg net/socket.c:664 [inline] __sys_sendto+0x467/0x620 net/socket.c:2006 __do_sys_sendto net/socket.c:2018 [inline] __se_sys_sendto net/socket.c:2014 [inline] __x64_sys_sendto+0xe5/0x100 net/socket.c:2014 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb page last free stack trace: reset_page_owner include/linux/page_owner.h:28 [inline] free_pages_prepare mm/page_alloc.c:1349 [inline] __free_pages_ok+0x80b/0x830 mm/page_alloc.c:1629 free_the_page mm/page_alloc.c:5445 [inline] __free_pages+0xd8/0x390 mm/page_alloc.c:5454 kfree+0x1e4/0x270 mm/slub.c:4193 skb_free_head net/core/skbuff.c:606 [inline] skb_release_data+0x53b/0x690 net/core/skbuff.c:626 skb_release_all net/core/skbuff.c:680 [inline] __kfree_skb net/core/skbuff.c:694 [inline] consume_skb+0xab/0x1f0 net/core/skbuff.c:851 skb_free_datagram+0x28/0xe0 net/core/datagram.c:325 netlink_recvmsg+0x5dd/0xe60 net/netlink/af_netlink.c:1993 ____sys_recvmsg+0x2ca/0x5b0 net/socket.c:-1 ___sys_recvmsg+0x213/0x5c0 net/socket.c:2637 __sys_recvmsg net/socket.c:2667 [inline] __do_sys_recvmsg net/socket.c:2677 [inline] __se_sys_recvmsg net/socket.c:2674 [inline] __x64_sys_recvmsg+0x1fe/0x2d0 net/socket.c:2674 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb Memory state around the buggy address: ffff88811d602b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88811d602c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff88811d602c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88811d602d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88811d602d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== ------------[ cut here ]------------ WARNING: CPU: 0 PID: 657 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: 657 Comm: syz.3.81 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 fc 0b 36 fd be 02 00 00 00 eb 0a e8 f0 0b 36 fd be 01 00 00 00 4c 89 f7 e8 a3 76 0f fe e9 0f ff ff ff e8 d9 0b 36 fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 c8 0b 36 fd 4c 89 f7 be 03 RSP: 0018:ffffc90000eafd68 EFLAGS: 00010293 RAX: ffffffff842e9627 RBX: ffff88811dd6d800 RCX: ffff88811d043b40 RDX: 0000000000000000 RSI: 000000001a519688 RDI: 000000000c04eb7d RBP: ffffc90000eafd88 R08: ffff88811dd6d883 R09: 1ffff11023badb10 R10: dffffc0000000000 R11: ffffed1023badb11 R12: dffffc0000000000 R13: dffffc0000000000 R14: 000000001a519688 R15: ffff88811d602c00 FS: 000055558350c500(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f18a5c5b540 CR3: 000000011cfa5000 CR4: 00000000003506b0 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:597 [inline] sock_close+0xb8/0x200 net/socket.c:1286 __fput+0x2dc/0x730 fs/file_table.c:281 ____fput+0x15/0x20 fs/file_table.c:314 task_work_run+0x127/0x190 kernel/task_work.c:189 tracehook_notify_resume include/linux/tracehook.h:188 [inline] exit_to_user_mode_loop+0xcb/0xe0 kernel/entry/common.c:172 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:199 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:274 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f18a5c0de59 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:00007ffd7e986118 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 00007f18a5e88da0 RCX: 00007f18a5c0de59 RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003 RBP: 00007f18a5e88da0 R08: 0000000000000006 R09: 0000000000000000 R10: 000000000003fd64 R11: 0000000000000246 R12: 0000000000009f86 R13: 00007f18a5e8709c R14: 0000000000009d38 R15: 00007f18a5e87090 ---[ end trace e1314d8928b3f518 ]---