l2tp_ppp: tunl 4: set debug=cf10464f BUG: unable to handle kernel NULL pointer dereference at 0000000000000080 IP: [] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1671 PGD bb245067 PUD b751c067 PMD 0 Oops: 0002 [#1] PREEMPT SMP KASAN Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: CPU: 0 PID: 16239 Comm: syz-executor3 Not tainted 4.4.138-gcf21a9a #64 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 task: ffff8800a741c800 task.stack: ffff8800b5450000 RIP: 0010:[] [] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1671 RSP: 0018:ffff8800b54578c8 EFLAGS: 00010246 RAX: dffffc0000000000 RBX: ffff8800a73c0780 RCX: 0000000000000000 RDX: 1ffff100382ba8d0 RSI: ffffffff8359d061 RDI: ffff8801c15d4680 RBP: ffff8800b54578e8 R08: ffffffff853504b0 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801c15d4500 R13: ffff8800a73c0788 R14: 0000000000000000 R15: ffffffff82f1a2b0 FS: 00007f3a92358700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000080 CR3: 00000000b9b2b000 CR4: 00000000001606f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Stack: ffff8800b03d0880 ffff8800a73c0780 ffff8800b03d0c50 ffff8800b03d0b58 ffff8800b5457910 ffffffff835a6b07 ffff8800b03d0880 ffffffff835a6a30 ffff8801bbc46220 ffff8800b5457938 ffffffff82f2f31c ffff8800b03d0880 Call Trace: [] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline] [] pppol2tp_session_destruct+0xd7/0x110 net/l2tp/l2tp_ppp.c:477 [] sk_destruct+0x4c/0x4c0 net/core/sock.c:1447 [] __sk_free+0x4f/0x220 net/core/sock.c:1480 [] sk_free+0x30/0x40 net/core/sock.c:1491 [] sock_put include/net/sock.h:1639 [inline] [] pppol2tp_release+0x26a/0x310 net/l2tp/l2tp_ppp.c:518 [] 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 Code: 49 8d bc 24 80 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 d0 00 00 00 4d 8b b4 24 80 01 00 00 41 ff 8e 80 00 00 00 74 64 e8 15 44 db fd e8 10 44 db fd 4c RIP [] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1671 RSP CR2: 0000000000000080 ---[ end trace dee6bc70148eb8e9 ]---