================================================================== BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156 Read of size 4 at addr ffff88810eba2800 by task syz.0.183/1160 CPU: 0 PID: 1160 Comm: syz.0.183 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 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_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:597 [inline] sock_close+0xb8/0x200 net/socket.c:1287 __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:175 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:202 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:277 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f83746a5559 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:00007ffdca53e188 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 00007f837492eda0 RCX: 00007f83746a5559 RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003 RBP: 00007f837492eda0 R08: 0000000000000006 R09: 0000000000000000 R10: 00007f837492ecb0 R11: 0000000000000246 R12: 000000000000c777 R13: 00007f837492d09c R14: 000000000000c4a3 R15: 00007f837492d090 Allocated by task 1161: 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:1867 [inline] __sys_connect+0x3ce/0x450 net/socket.c:1884 __do_sys_connect net/socket.c:1894 [inline] __se_sys_connect net/socket.c:1891 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:1891 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb Freed by task 1162: 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+0x1e1/0x440 drivers/net/ppp/pppox.c:110 sock_do_ioctl+0xda/0x380 net/socket.c:1068 sock_ioctl+0x472/0x740 net/socket.c:1208 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 ffff88810eba2800 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 0 bytes inside of 512-byte region [ffff88810eba2800, ffff88810eba2a00) The buggy address belongs to the page: page:ffffea00043ae800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10eba0 head:ffffea00043ae800 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 dead000000000100 dead000000000122 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 283, ts 24403793386, free_ts 24367832279 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] kmem_cache_alloc_trace+0x1a8/0x2e0 mm/slub.c:2977 kmalloc include/linux/slab.h:555 [inline] kzalloc include/linux/slab.h:667 [inline] ipv6_add_addr+0x408/0xd90 net/ipv6/addrconf.c:1113 inet6_addr_add+0x453/0x970 net/ipv6/addrconf.c:3031 inet6_rtm_newaddr+0x6e1/0x9c0 net/ipv6/addrconf.c:4977 rtnetlink_rcv_msg+0x9e9/0xca0 net/core/rtnetlink.c:5622 netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2508 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5640 netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline] netlink_unicast+0x86c/0xa30 net/netlink/af_netlink.c:1340 netlink_sendmsg+0x949/0xb70 net/netlink/af_netlink.c:1919 sock_sendmsg_nosec net/socket.c:652 [inline] __sock_sendmsg net/socket.c:664 [inline] __sys_sendto+0x467/0x620 net/socket.c:2007 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 __free_slab+0xcf/0x190 mm/slub.c:1899 free_slab mm/slub.c:1914 [inline] discard_slab mm/slub.c:1920 [inline] unfreeze_partials+0x150/0x180 mm/slub.c:2415 put_cpu_partial+0xc1/0x180 mm/slub.c:2451 __slab_free+0x2c9/0x3a0 mm/slub.c:3100 do_slab_free mm/slub.c:3196 [inline] ___cache_free+0x10e/0x130 mm/slub.c:3215 qlink_free+0x50/0x90 mm/kasan/quarantine.c:157 qlist_free_all+0x5f/0xb0 mm/kasan/quarantine.c:176 kasan_quarantine_reduce+0x14a/0x160 mm/kasan/quarantine.c:283 __kasan_slab_alloc+0x2f/0xe0 mm/kasan/common.c:440 kasan_slab_alloc include/linux/kasan.h:244 [inline] slab_post_alloc_hook+0x5d/0x2f0 mm/slab.h:580 slab_alloc_node mm/slub.c:2952 [inline] slab_alloc mm/slub.c:2960 [inline] __kmalloc+0x17b/0x330 mm/slub.c:4034 __kmalloc_node include/linux/slab.h:421 [inline] kmalloc_node include/linux/slab.h:578 [inline] kzalloc_node include/linux/slab.h:678 [inline] qdisc_alloc+0x79/0x720 net/sched/sch_generic.c:865 qdisc_create_dflt+0x6b/0x390 net/sched/sch_generic.c:928 attach_one_default_qdisc net/sched/sch_generic.c:1091 [inline] netdev_for_each_tx_queue include/linux/netdevice.h:2323 [inline] attach_default_qdiscs net/sched/sch_generic.c:1109 [inline] dev_activate+0x292/0x11c0 net/sched/sch_generic.c:1168 Memory state around the buggy address: ffff88810eba2700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88810eba2780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff88810eba2800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88810eba2880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88810eba2900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== ------------[ cut here ]------------ WARNING: CPU: 0 PID: 1160 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: 1160 Comm: syz.0.183 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 bc f7 34 fd be 02 00 00 00 eb 0a e8 b0 f7 34 fd be 01 00 00 00 4c 89 f7 e8 33 73 0e fe e9 0f ff ff ff e8 99 f7 34 fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 88 f7 34 fd 4c 89 f7 be 03 RSP: 0018:ffffc90001c47d68 EFLAGS: 00010293 RAX: ffffffff842fbf27 RBX: ffff888115c79000 RCX: ffff888100df8000 RDX: 0000000000000000 RSI: 000000001fd85020 RDI: 000000000c04eb7d RBP: ffffc90001c47d88 R08: 0000000000000003 R09: 0000000000000004 R10: dffffc0000000000 R11: fffffbfff0dcf848 R12: dffffc0000000000 R13: dffffc0000000000 R14: 000000001fd85020 R15: ffff88810eba2800 FS: 0000555555f6c500(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055c196ec2af8 CR3: 0000000114164000 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:1287 __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:175 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:202 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:277 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f83746a5559 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:00007ffdca53e188 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 00007f837492eda0 RCX: 00007f83746a5559 RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003 RBP: 00007f837492eda0 R08: 0000000000000006 R09: 0000000000000000 R10: 00007f837492ecb0 R11: 0000000000000246 R12: 000000000000c777 R13: 00007f837492d09c R14: 000000000000c4a3 R15: 00007f837492d090 ---[ end trace 5ab03a3a8da3da0a ]---