bisecting fixing commit since 01364dad1d4577e27a57729d41053f661bb8a5b9 building syzkaller on aa6c6a5572a4797ea6109a75ca50a2c86908375e testing commit 01364dad1d4577e27a57729d41053f661bb8a5b9 with gcc (GCC) 8.1.0 kernel signature: 29760051bcd9bf723b74aaf643dc7f5b6a8aefe819d58268e79e19c31a3735fe run #0: crashed: WARNING in inet_sock_destruct run #1: crashed: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free run #2: crashed: WARNING in inet_sock_destruct run #3: crashed: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free run #4: crashed: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free run #5: crashed: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free run #6: crashed: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free run #7: crashed: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free run #8: crashed: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free run #9: crashed: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free testing current HEAD 773e2b1cd56a17bab4cdd4fe7db12f2140951668 testing commit 773e2b1cd56a17bab4cdd4fe7db12f2140951668 with gcc (GCC) 8.1.0 kernel signature: 965ef380a6db0cdfe58fc9775d0653292c20583914bee781671d037ecda39166 all runs: crashed: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free revisions tested: 2, total time: 24m54.782799726s (build: 17m35.916183513s, test: 6m20.027338553s) the crash still happens on HEAD commit msg: Linux 4.14.178 crash: BUG: unable to handle kernel NULL pointer dereference in l2tp_session_free IPv6: ADDRCONF(NETDEV_CHANGE): veth1_macvtap: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): veth0_macvtap: link becomes ready batman_adv: The newly added mac address (aa:aa:aa:aa:aa:3e) already exists on: batadv_slave_1 batman_adv: It is strongly recommended to keep mac addresses unique to avoid problems! batman_adv: The newly added mac address (aa:aa:aa:aa:aa:3e) already exists on: batadv_slave_1 BUG: unable to handle kernel NULL pointer dereference at 0000000000000080 batman_adv: It is strongly recommended to keep mac addresses unique to avoid problems! IP: refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline] IP: sock_put include/net/sock.h:1657 [inline] IP: l2tp_session_free+0xfd/0x1d0 net/l2tp/l2tp_core.c:1714 PGD a5959067 P4D a5959067 PUD a850e067 PMD 0 Oops: 0002 [#1] PREEMPT SMP KASAN Modules linked in: CPU: 1 PID: 7765 Comm: syz-executor.3 Not tainted 4.14.178-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 task: ffff8880a5706680 task.stack: ffff8880a6600000 RIP: 0010:refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline] RIP: 0010:sock_put include/net/sock.h:1657 [inline] RIP: 0010:l2tp_session_free+0xfd/0x1d0 net/l2tp/l2tp_core.c:1714 RSP: 0018:ffff8880a6607c80 EFLAGS: 00010246 RAX: dffffc0000000000 RBX: ffff888085359040 RCX: 0000000000000000 RDX: 1ffff11014ada939 RSI: ffff8880a5706f08 RDI: 0000000000000000 RBP: ffff8880a6607c98 R08: ffff8880a5706f28 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880a56d4840 R13: ffff888085359050 R14: ffff888085316d20 R15: ffffffff87664f80 FS: 0000000000cd0940(0000) GS:ffff8880aed00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000080 CR3: 00000000a5958000 CR4: 00000000001406e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:300 [inline] pppol2tp_session_destruct+0xbb/0xf0 net/l2tp/l2tp_ppp.c:460 __sk_destruct+0x48/0x5a0 net/core/sock.c:1556 sk_destruct+0x83/0xb0 net/core/sock.c:1596 __sk_free+0x47/0x1f0 net/core/sock.c:1604 sk_free+0x1a/0x20 net/core/sock.c:1615 sock_put include/net/sock.h:1658 [inline] pppol2tp_release+0x218/0x2a0 net/l2tp/l2tp_ppp.c:501 __sock_release+0xc2/0x2a0 net/socket.c:602 sock_close+0x10/0x20 net/socket.c:1139 __fput+0x232/0x750 fs/file_table.c:210 ____fput+0x9/0x10 fs/file_table.c:244 task_work_run+0xe5/0x170 kernel/task_work.c:113 tracehook_notify_resume include/linux/tracehook.h:191 [inline] exit_to_usermode_loop+0x16a/0x1b0 arch/x86/entry/common.c:164 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline] syscall_return_slowpath arch/x86/entry/common.c:270 [inline] do_syscall_64+0x416/0x5b0 arch/x86/entry/common.c:297 entry_SYSCALL_64_after_hwframe+0x42/0xb7 RIP: 0033:0x4163e1 IPv6: ADDRCONF(NETDEV_UP): batadv_slave_1: link is not ready RSP: 002b:00007ffc5aa21ae0 EFLAGS: 00000293 batman_adv: batadv0: Interface activated: batadv_slave_1 ORIG_RAX: 0000000000000003 device veth0_macvtap entered promiscuous mode RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00000000004163e1 IPv6: ADDRCONF(NETDEV_UP): macvtap0: link is not ready RDX: 0000000000000001 RSI: 00000000007700c8 RDI: 0000000000000003 RBP: 0000000000000000 R08: 01ffffffffffffff R09: 01ffffffffffffff R10: 00007ffc5aa21bc0 R11: 0000000000000293 R12: 000000000076c040 R13: 0000000000770778 R14: 000000000000bffc R15: 000000000076c04c Code: 49 8d bc 24 88 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 bd 00 00 00 49 8b bc 24 88 01 00 00 ff 8f 80 00 00 00 0f 88 35 62 7f 00 74 6d 48 b8 00 00 00 00 RIP: refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline] RSP: ffff8880a6607c80 RIP: sock_put include/net/sock.h:1657 [inline] RSP: ffff8880a6607c80 RIP: l2tp_session_free+0xfd/0x1d0 net/l2tp/l2tp_core.c:1714 RSP: ffff8880a6607c80 CR2: 0000000000000080 ---[ end trace 6de28a866e284743 ]--- IPv6: ADDRCONF(NETDEV_UP): veth1_macvtap: link is not ready