WARNING: refcount bug in cdev

WARNING: refcount bug in cdev_get
Status: fixed on 2020/01/24 06:24
Reported-by: syzbot+8f6326d01bc61afbc095@syzkaller.appspotmail.com
Fix commit: 03a70959 net: usb: lan78xx: Connect PHY before registering MAC
First crash: 329d, last: 199d

Fix bisection: fixed by (bisect log):

commit 03a70959304028f2eed3713f03bd1c92585699b0
Author: Andrew Lunn <andrew@lunn.ch>
Date: Thu Oct 17 19:29:26 2019 +0000

net: usb: lan78xx: Connect PHY before registering MAC

similar bugs (2):
Kernel	Title	Repro	Bisected	Count	Last	Reported	Patched	Status
linux-4.19	WARNING: refcount bug in cdev_get	C	fix	12	203d	329d	1/1	fixed on 2020/01/19 15:05
upstream	WARNING: refcount bug in cdev_get	C	cause	105	185d	325d	16/17	fixed on 2020/02/18 14:31

Sample crash report:

input: syz1 as /devices/virtual/input/input1191
input: syz1 as /devices/virtual/input/input1192
refcount_t: increment on 0; use-after-free.
------------[ cut here ]------------
kobject: '(null)' (ffff888098f28968): calling ktype release
WARNING: CPU: 1 PID: 12651 at lib/refcount.c:153 refcount_inc lib/refcount.c:153 [inline]
WARNING: CPU: 1 PID: 12651 at lib/refcount.c:153 refcount_inc.cold+0x18/0x1f lib/refcount.c:151
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 12651 Comm: syz-executor938 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:ffff88808f92f980 EFLAGS: 00010286
RAX: 000000000000002b RBX: 1ffff11011f25f3d RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff866d10e0 RDI: ffffed1011f25f26
RBP: ffff88808f92f988 R08: 000000000000002b R09: ffff8880a1aca960
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888098f289a0
R13: 0000000000000000 R14: ffff888096237500 R15: ffff888093d2e488
 kref_get include/linux/kref.h:47 [inline]
 kobject_get+0x5b/0x70 lib/kobject.c:596
 cdev_get+0x54/0xa0 fs/char_dev.c:364
 chrdev_open+0x9b/0x590 fs/char_dev.c:409
 do_dentry_open+0x73b/0xeb0 fs/open.c:777
 vfs_open+0x105/0x220 fs/open.c:891
 do_last fs/namei.c:3425 [inline]
 path_openat+0x8bd/0x3f70 fs/namei.c:3566
 do_filp_open+0x18e/0x250 fs/namei.c:3600
 do_sys_open+0x2c5/0x430 fs/open.c:1084
 SYSC_open fs/open.c:1102 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1097
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x405831
RSP: 002b:00007f487cd9e960 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000405831
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007f487cd9e970
RBP: 6666666666666667 R08: 000000000000000f R09: 00007f487cd9f700
R10: 00007f487cd9f9d0 R11: 0000000000000293 R12: 00000000006dbc3c
R13: 000000000000001f R14: 0000000000000000 R15: 00000000317a7973
Kernel Offset: disabled
Rebooting in 86400 seconds..

Crashes (21):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	Maintainers
ci2-linux-4-14	2019/10/02 21:38	linux-4.14.y	f6e27dbb	2e29b534	.config	log	report	syz	C	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/09/23 04:13	linux-4.14.y	f6e27dbb	d96e88f3	.config	log	report	syz	C	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/09/16 10:11	linux-4.14.y	968722f5	55c50e70	.config	log	report	syz	C	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/08/16 22:46	linux-4.14.y	45f092f9	8fd428a1	.config	log	report	syz	C	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/11/25 01:30	linux-4.14.y	43598c57	598ca6c8	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/11/01 10:34	linux-4.14.y	ddef1e8e	a41ca8fa	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/10/30 03:01	linux-4.14.y	ddef1e8e	5ea87a66	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/10/26 12:30	linux-4.14.y	b98aebd2	25bb509e	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/10/25 08:09	linux-4.14.y	b98aebd2	d01bb02a	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/10/12 14:24	linux-4.14.y	e132c8d7	426631dd	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/10/11 01:25	linux-4.14.y	42327896	1a3bad90	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/09/28 01:33	linux-4.14.y	f6e27dbb	d8074e0b	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/09/27 04:40	linux-4.14.y	f6e27dbb	2f1548bc	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/09/26 20:30	linux-4.14.y	f6e27dbb	2f1548bc	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/09/24 18:46	linux-4.14.y	f6e27dbb	f8368f99	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/09/21 17:03	linux-4.14.y	f6e27dbb	d96e88f3	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/09/09 22:41	linux-4.14.y	414510bc	a60cb4cd	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/09/02 05:52	linux-4.14.y	01fd1694	db7c31ca	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/08/23 16:47	linux-4.14.y	45f092f9	78ded196	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/08/19 05:16	linux-4.14.y	45f092f9	b8ceabfc	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/08/17 18:44	linux-4.14.y	45f092f9	55bf8926	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk