WARNING: refcount bug in kobject

WARNING: refcount bug in kobject_get
Status: upstream: reported C repro on 2019/04/14 10:44
Reported-by: syzbot+122b2c22c75de10ba756@syzkaller.appspotmail.com
First crash: 217d, last: 98d

similar bugs (2):
Kernel	Title	Repro	Bisected	Count	Last	Reported	Patched	Status
upstream	WARNING: refcount bug in kobject_get	C		530	100d	433d	0/14	closed as invalid on 2019/08/19 12:30
linux-4.19	WARNING: refcount bug in kobject_get	C		21	96d	212d	0/1	upstream: reported C repro on 2019/04/18 16:23

Sample crash report:

input: syz0 as /devices/virtual/input/input1695
input: syz0 as /devices/virtual/input/input1696
input: syz0 as /devices/virtual/input/input1697
refcount_t: increment on 0; use-after-free.
------------[ cut here ]------------
WARNING: CPU: 1 PID: 10546 at lib/refcount.c:153 refcount_inc lib/refcount.c:153 [inline]
WARNING: CPU: 1 PID: 10546 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: 10546 Comm: syz-executor008 Not tainted 4.14.111 #1
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+0x138/0x19c lib/dump_stack.c:53
 panic+0x1f2/0x438 kernel/panic.c:182
 __warn.cold+0x2f/0x34 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:944
RIP: 0010:refcount_inc lib/refcount.c:153 [inline]
RIP: 0010:refcount_inc.cold+0x18/0x1f lib/refcount.c:151
RSP: 0018:ffff888099d9f980 EFLAGS: 00010286
RAX: 000000000000002b RBX: 1ffff110133b3f3d RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff8880a7d46dc0 RDI: ffffed10133b3f26
RBP: ffff888099d9f988 R08: 000000000000002b R09: ffff8880a7d46de0
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88808332d320
R13: 0000000000000000 R14: ffff88809df20780 R15: ffff8880969e4ee8
 kref_get include/linux/kref.h:47 [inline]
 kobject_get+0x5b/0x70 lib/kobject.c:596
 cdev_get+0x54/0xa0 fs/char_dev.c:358
 chrdev_open+0x9b/0x590 fs/char_dev.c:403
 do_dentry_open+0x73e/0xeb0 fs/open.c:758
 vfs_open+0x105/0x230 fs/open.c:872
 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:1065
 SYSC_open fs/open.c:1083 [inline]
 SyS_open+0x2d/0x40 fs/open.c:1078
 do_syscall_64+0x1eb/0x630 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x402ec0
RSP: 002b:00007ffc806bb038 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 000000000000000a RCX: 0000000000402ec0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffc806bb050
RBP: 0000000000000000 R08: 000000000000000f R09: 00000000000003e8
R10: 00000000000003e8 R11: 0000000000000246 R12: 0000000000000121
R13: 00000000004aacf0 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..

Crashes (20):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	Maintainers
ci2-linux-4-14	2019/04/14 12:01	linux-4.14.y	1ec8f1f0	505ab413	.config	log	report	syz	C	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/07/25 07:26	linux-4.14.y	ff33472c	32329ceb	.config	log	report	syz	C	gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
ci2-linux-4-14	2019/07/04 15:06	linux-4.14.y	e3c1b273	55565fa0	.config	log	report	syz	C	gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
ci2-linux-4-14	2019/04/27 06:58	linux-4.14.y	68d7a45e	b617407b	.config	log	report	syz	C	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/04/26 11:12	linux-4.14.y	68d7a45e	b617407b	.config	log	report	syz	C	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/04/23 21:11	linux-4.14.y	68d7a45e	2398edea	.config	log	report	syz	C	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/05/04 05:59	linux-4.14.y	1c046f37	d28f4ce5	.config	log	report	syz		linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/04/28 17:09	linux-4.14.y	fa5941f4	b617407b	.config	log	report	syz		linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/04/14 09:43	linux-4.14.y	1ec8f1f0	505ab413	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/08/10 16:28	linux-4.14.y	3ffe1e79	acb51638	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/08/03 08:43	linux-4.14.y	10d6aa56	6affd8e8	.config	log	report			gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
ci2-linux-4-14	2019/07/30 17:27	linux-4.14.y	ff33472c	f28bf2a5	.config	log	report			gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
ci2-linux-4-14	2019/07/25 18:04	linux-4.14.y	ff33472c	0d7a1249	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/07/01 00:08	linux-4.14.y	f4cc0ed9	699d6448	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/06/26 08:44	linux-4.14.y	bc2bccef	0a8d1a96	.config	log	report			gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
ci2-linux-4-14	2019/06/21 07:56	linux-4.14.y	bb263a2a	34bf9440	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci2-linux-4-14	2019/06/20 00:37	linux-4.14.y	bb263a2a	34bf9440	.config	log	report			gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
ci2-linux-4-14	2019/06/14 15:25	linux-4.14.y	2bf3258a	998ccc76	.config	log	report			gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
ci2-linux-4-14	2019/06/11 10:30	linux-4.14.y	e6a95d88	5b5826d0	.config	log	report			gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
ci2-linux-4-14	2019/04/26 15:13	linux-4.14.y	68d7a45e	b617407b	.config	log	report			linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk