refcount_t: increment on 0; use-after-free. ------------[ cut here ]------------ WARNING: CPU: 0 PID: 19911 at lib/refcount.c:153 refcount_inc lib/refcount.c:153 [inline] WARNING: CPU: 0 PID: 19911 at lib/refcount.c:153 refcount_inc.cold+0x18/0x1f lib/refcount.c:151 Kernel panic - not syncing: panic_on_warn set ... CPU: 0 PID: 19911 Comm: syz-executor.4 Not tainted 4.14.146 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x138/0x197 lib/dump_stack.c:53 panic+0x1f2/0x426 kernel/panic.c:182 __warn.cold+0x2f/0x36 kernel/panic.c:546 report_bug+0x216/0x254 lib/bug.c:186 fixup_bug arch/x86/kernel/traps.c:177 [inline] fixup_bug arch/x86/kernel/traps.c:172 [inline] do_error_trap+0x1bb/0x310 arch/x86/kernel/traps.c:295 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:314 invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:963 RIP: 0010:refcount_inc lib/refcount.c:153 [inline] RIP: 0010:refcount_inc.cold+0x18/0x1f lib/refcount.c:151 RSP: 0018:ffff8880953dfb70 EFLAGS: 00010286 RAX: 000000000000002b RBX: ffff88808e1c6248 RCX: 0000000000000000 RDX: 00000000000094ec RSI: ffffffff814b2e55 RDI: ffffed1012a7bf64 RBP: ffff8880953dfb78 R08: 000000000000002b R09: ffff88808c862bf0 R10: 0000000000000000 R11: 0000000000000000 R12: ffff888098f6e180 R13: 0000000000000000 R14: ffff888054d59ae0 R15: ffff888054d59ac0 sock_hold include/net/sock.h:619 [inline] l2tp_session_add_to_tunnel net/l2tp/l2tp_core.c:368 [inline] l2tp_session_create+0x118b/0x1600 net/l2tp/l2tp_core.c:1846 pppol2tp_connect+0x11bf/0x18b0 net/l2tp/l2tp_ppp.c:721 SYSC_connect+0x1f6/0x2d0 net/socket.c:1655 SyS_connect+0x24/0x30 net/socket.c:1636 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x42/0xb7 RIP: 0033:0x459a29 RSP: 002b:00007f3a0352bc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459a29 RDX: 000000000000002e RSI: 0000000020000000 RDI: 0000000000000005 RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f3a0352c6d4 R13: 00000000004bff97 R14: 00000000004d2218 R15: 00000000ffffffff Kernel Offset: disabled Rebooting in 86400 seconds..