================================================================== BUG: KASAN: use-after-free in pppol2tp_sock_to_session+0x1a0/0x1b0 net/l2tp/l2tp_ppp.c:156 Read of size 4 at addr ffff88810ef21400 by task syz.3.83/648 CPU: 0 PID: 648 Comm: syz.3.83 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 exit_task_work include/linux/task_work.h:33 [inline] do_exit+0xa7c/0x24e0 kernel/exit.c:873 __do_sys_exit kernel/exit.c:956 [inline] __se_sys_exit kernel/exit.c:954 [inline] __x64_sys_exit+0x40/0x40 kernel/exit.c:954 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f74c7a250d9 Code: Unable to access opcode bytes at RIP 0x7f74c7a250af. RSP: 002b:00007f74c647def8 EFLAGS: 00000246 ORIG_RAX: 000000000000003c RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f74c7a250d9 RDX: 00007f74c647e9c8 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 00007f74c7abc024 R08: 0000000000000000 R09: 0000000000000058 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f74c7cad038 R14: 00007f74c7cacfa0 R15: 00007ffd8a43be98 Allocated by task 645: 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 300: 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 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+0x6fd/0xbc0 kernel/workqueue.c:2301 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447 kthread+0x324/0x3b0 kernel/kthread.c:313 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298 The buggy address belongs to the object at ffff88810ef21400 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 0 bytes inside of 512-byte region [ffff88810ef21400, ffff88810ef21600) The buggy address belongs to the page: page:ffffea00043bc800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10ef20 head:ffffea00043bc800 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 ffffea000470c600 0000000400000004 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 15, ts 7283705740, free_ts 7283526429 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+0x1f9/0x330 mm/slub.c:4034 __kmalloc_node include/linux/slab.h:421 [inline] kmalloc_node include/linux/slab.h:578 [inline] kvmalloc_node+0x88/0x130 mm/util.c:612 kvmalloc include/linux/mm.h:833 [inline] kvzalloc include/linux/mm.h:841 [inline] bucket_table_alloc lib/rhashtable.c:184 [inline] rhashtable_rehash_alloc+0x36/0x2f0 lib/rhashtable.c:360 rht_deferred_worker+0x2e0/0x1050 lib/rhashtable.c:-1 process_one_work+0x6fd/0xbc0 kernel/workqueue.c:2301 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447 kthread+0x324/0x3b0 kernel/kthread.c:313 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298 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_pcp_prepare mm/page_alloc.c:1421 [inline] free_unref_page_prepare+0x2b7/0x2d0 mm/page_alloc.c:3336 free_unref_page_list+0x129/0x9c0 mm/page_alloc.c:3443 release_pages+0xe41/0xe90 mm/swap.c:1103 free_pages_and_swap_cache+0x86/0xa0 mm/swap_state.c:356 tlb_batch_pages_flush mm/mmu_gather.c:49 [inline] tlb_flush_mmu_free mm/mmu_gather.c:240 [inline] tlb_flush_mmu mm/mmu_gather.c:247 [inline] tlb_finish_mmu+0x17e/0x310 mm/mmu_gather.c:326 exit_mmap+0x329/0x590 mm/mmap.c:3387 __mmput+0x92/0x2d0 kernel/fork.c:1153 mmput+0x4e/0x150 kernel/fork.c:1176 exit_mm kernel/exit.c:540 [inline] do_exit+0x9d8/0x24e0 kernel/exit.c:860 do_group_exit+0x149/0x310 kernel/exit.c:987 __do_sys_exit_group kernel/exit.c:998 [inline] __se_sys_exit_group kernel/exit.c:996 [inline] __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:996 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb Memory state around the buggy address: ffff88810ef21300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88810ef21380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff88810ef21400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88810ef21480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88810ef21500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== ------------[ cut here ]------------ WARNING: CPU: 1 PID: 648 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: 648 Comm: syz.3.83 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 8c dc 35 fd be 02 00 00 00 eb 0a e8 80 dc 35 fd be 01 00 00 00 4c 89 f7 e8 f3 32 0f fe e9 0f ff ff ff e8 69 dc 35 fd <0f> 0b 48 89 df e8 ef 00 00 00 eb bd e8 58 dc 35 fd 4c 89 f7 be 03 RSP: 0018:ffffc90000f67c40 EFLAGS: 00010293 RAX: ffffffff842ec977 RBX: ffff88811c32d000 RCX: ffff88811a120000 RDX: 0000000000000000 RSI: 000000001c1db200 RDI: 000000000c04eb7d RBP: ffffc90000f67c60 R08: 0000000000000003 R09: 0000000000000004 R10: dffffc0000000000 R11: fffffbfff0dcf648 R12: dffffc0000000000 R13: dffffc0000000000 R14: 000000001c1db200 R15: ffff88810ef21400 FS: 0000000000000000(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f78143822f8 CR3: 0000000124b7e000 CR4: 00000000003506a0 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 exit_task_work include/linux/task_work.h:33 [inline] do_exit+0xa7c/0x24e0 kernel/exit.c:873 __do_sys_exit kernel/exit.c:956 [inline] __se_sys_exit kernel/exit.c:954 [inline] __x64_sys_exit+0x40/0x40 kernel/exit.c:954 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb RIP: 0033:0x7f74c7a250d9 Code: Unable to access opcode bytes at RIP 0x7f74c7a250af. RSP: 002b:00007f74c647def8 EFLAGS: 00000246 ORIG_RAX: 000000000000003c RAX: ffffffffffffffda RBX: 0000000000000058 RCX: 00007f74c7a250d9 RDX: 00007f74c647e9c8 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 00007f74c7abc024 R08: 0000000000000000 R09: 0000000000000058 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f74c7cad038 R14: 00007f74c7cacfa0 R15: 00007ffd8a43be98 ---[ end trace 641d09d66f8dce91 ]---