================================================================== BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830 Read of size 4 at addr ffff8800ba6c6780 by task syz-executor816/5636 CPU: 1 PID: 5636 Comm: syz-executor816 Not tainted 4.4.138-gcf21a9a #64 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 0000000000000000 3d4336ddebff43a9 ffff8800b995f8b0 ffffffff81e0ed0d ffffea0002e9b180 ffff8800ba6c6780 0000000000000000 ffff8800ba6c6780 ffffffff82f1a2b0 ffff8800b995f8e8 ffffffff81515a16 ffff8800ba6c6780 Call Trace: [] __dump_stack lib/dump_stack.c:15 [inline] [] dump_stack+0xc1/0x124 lib/dump_stack.c:51 [] print_address_description+0x6c/0x216 mm/kasan/report.c:252 [] kasan_report_error mm/kasan/report.c:351 [inline] [] kasan_report.cold.7+0x175/0x2f7 mm/kasan/report.c:408 [] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428 [] l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:830 [] pppol2tp_release+0x1ff/0x310 net/l2tp/l2tp_ppp.c:509 [] sock_release+0x96/0x1c0 net/socket.c:586 [] sock_close+0x16/0x20 net/socket.c:1037 [] __fput+0x235/0x6f0 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0x10f/0x190 kernel/task_work.c:115 [] exit_task_work include/linux/task_work.h:21 [inline] [] do_exit+0x9e5/0x26b0 kernel/exit.c:759 [] do_group_exit+0x111/0x330 kernel/exit.c:889 [] get_signal+0x4ec/0x14b0 kernel/signal.c:2321 [] do_signal+0x8b/0x1d30 arch/x86/kernel/signal.c:712 [] exit_to_usermode_loop+0x11a/0x160 arch/x86/entry/common.c:248 [] prepare_exit_to_usermode arch/x86/entry/common.c:283 [inline] [] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:348 [] int_ret_from_sys_call+0x25/0xa3 Allocated by task 5636: [] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63 [] save_stack+0x43/0xd0 mm/kasan/kasan.c:512 [] set_track mm/kasan/kasan.c:524 [inline] [] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:616 [] __kmalloc+0x124/0x310 mm/slub.c:3613 [] kmalloc include/linux/slab.h:481 [inline] [] kzalloc include/linux/slab.h:620 [inline] [] l2tp_session_create+0x39/0x1030 net/l2tp/l2tp_core.c:1748 [] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725 [] SYSC_connect+0x1b8/0x300 net/socket.c:1557 [] SyS_connect+0x24/0x30 net/socket.c:1538 [] entry_SYSCALL_64_fastpath+0x22/0x9e Freed by task 5588: [] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63 [] save_stack+0x43/0xd0 mm/kasan/kasan.c:512 [] set_track mm/kasan/kasan.c:524 [inline] [] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589 [] slab_free_hook mm/slub.c:1383 [inline] [] slab_free_freelist_hook mm/slub.c:1405 [inline] [] slab_free mm/slub.c:2859 [inline] [] kfree+0xf4/0x310 mm/slub.c:3749 [] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1676 [] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline] [] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279 [] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300 [] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421 [] sk_common_release+0x6d/0x300 net/core/sock.c:2680 [] udp_lib_close+0x15/0x20 include/net/udp.h:190 [] inet_release+0xff/0x1d0 net/ipv4/af_inet.c:435 [] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424 [] sock_release+0x96/0x1c0 net/socket.c:586 [] sock_close+0x16/0x20 net/socket.c:1037 [] __fput+0x235/0x6f0 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0x10f/0x190 kernel/task_work.c:115 [] exit_task_work include/linux/task_work.h:21 [inline] [] do_exit+0x9e5/0x26b0 kernel/exit.c:759 [] do_group_exit+0x111/0x330 kernel/exit.c:889 [] SYSC_exit_group kernel/exit.c:900 [inline] [] SyS_exit_group+0x1d/0x20 kernel/exit.c:898 [] entry_SYSCALL_64_fastpath+0x22/0x9e The buggy address belongs to the object at ffff8800ba6c6780 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 0 bytes inside of 512-byte region [ffff8800ba6c6780, ffff8800ba6c6980) The buggy address belongs to the page: kasan: CONFIG_KASAN_INLINE enabled kasan: GPF could be caused by NULL-ptr deref or user memory accessgeneral protection fault: 0000 [#1] PREEMPT SMP KASAN Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: CPU: 0 PID: 3839 Comm: sshd Not tainted 4.4.138-gcf21a9a #64 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 task: ffff8800ab809800 task.stack: ffff8800ba6c6980 RIP: 0010:[] [] __debug_check_no_obj_freed lib/debugobjects.c:689 [inline] RIP: 0010:[] [] debug_check_no_obj_freed+0x1a6/0x940 lib/debugobjects.c:726 RSP: 0000:ffff8801d94374b8 EFLAGS: 00010807 RAX: 0000000000000286 RBX: 8580012500001604 RCX: ffffffff81e71d3e RDX: 10b00024a00002c0 RSI: 0000000000000004 RDI: ffff8800ba6c6998 RBP: ffff8801d94375a0 R08: ffff8801d9437538 R09: dead000000000200 R10: 0000000000000001 R11: ffff8800ab809800 R12: 8580012500001604 R13: dffffc0000000000 R14: ffffffff85a0c628 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000006980ffff CR3: 000000000440c000 CR4: 00000000001606f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Stack: ffff8800ab80a0d8 ffff8801d9437538 ffffffff85a0c620 ffff88021fb55000 ffff88021fb55000 0000000000000004 0000000000000286 0000000000079e80 1ffff1003b286ea3 ffff88021fb54000 fffffbfff0b418c4 ffff88021fb54000 Call Trace: Code: [ 39.019741] ------------[ cut here ]------------ WARNING: CPU: 0 PID: -1167300736 at include/linux/uaccess.h:15 pagefault_disabled_dec include/linux/uaccess.h:15 [inline]() WARNING: CPU: 0 PID: -1167300736 at include/linux/uaccess.h:15 pagefault_enable include/linux/uaccess.h:42 [inline]() WARNING: CPU: 0 PID: -1167300736 at include/linux/uaccess.h:15 __probe_kernel_read+0x1b9/0x200 mm/maccess.c:35()