Re: [PATCH] pps: fix warning in pps_register_cdev when register device fail

[Wang Liang <wangliang74@huawei.com>]

在 2025/8/27 23:32, Calvin Owens 写道:
> On Wednesday 08/27 at 14:50 +0800, Wang Liang wrote:
>> Similar to previous commit 2a934fdb01db ("media: v4l2-dev: fix error
>> handling in __video_register_device()"), the release hook should be set
>> before device_register(). Otherwise, when device_register() return error
>> and put_device() try to callback the release function, the below warning
>> may happen.
>>
>>    ------------[ cut here ]------------
>>    WARNING: CPU: 1 PID: 4760 at drivers/base/core.c:2567 device_release+0x1bd/0x240 drivers/base/core.c:2567
>>    Modules linked in:
>>    CPU: 1 UID: 0 PID: 4760 Comm: syz.4.914 Not tainted 6.17.0-rc3+ #1 NONE
>>    RIP: 0010:device_release+0x1bd/0x240 drivers/base/core.c:2567
>>    Call Trace:
>>     <TASK>
>>     kobject_cleanup+0x136/0x410 lib/kobject.c:689
>>     kobject_release lib/kobject.c:720 [inline]
>>     kref_put include/linux/kref.h:65 [inline]
>>     kobject_put+0xe9/0x130 lib/kobject.c:737
>>     put_device+0x24/0x30 drivers/base/core.c:3797
>>     pps_register_cdev+0x2da/0x370 drivers/pps/pps.c:402
>>     pps_register_source+0x2f6/0x480 drivers/pps/kapi.c:108
>>     pps_tty_open+0x190/0x310 drivers/pps/clients/pps-ldisc.c:57
>>     tty_ldisc_open+0xa7/0x120 drivers/tty/tty_ldisc.c:432
>>     tty_set_ldisc+0x333/0x780 drivers/tty/tty_ldisc.c:563
>>     tiocsetd drivers/tty/tty_io.c:2429 [inline]
>>     tty_ioctl+0x5d1/0x1700 drivers/tty/tty_io.c:2728
>>     vfs_ioctl fs/ioctl.c:51 [inline]
>>     __do_sys_ioctl fs/ioctl.c:598 [inline]
>>     __se_sys_ioctl fs/ioctl.c:584 [inline]
>>     __x64_sys_ioctl+0x194/0x210 fs/ioctl.c:584
>>     do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>>     do_syscall_64+0x5f/0x2a0 arch/x86/entry/syscall_64.c:94
>>     entry_SYSCALL_64_after_hwframe+0x76/0x7e
>>     </TASK>
>>
>> Before commit c79a39dc8d06 ("pps: Fix a use-after-free"),
>> pps_register_cdev() call device_create() to create pps->dev, which will
>> init dev->release to device_create_release(). Now the comment is outdated,
>> just remove it.
> Hi Wang,
>
> I'm curious why pps_register_cdev() is failing, is there possibly a
> second issue to investigate there? Or was it fault injection?


I find this issue from my local syzkaller project.

Function pps_register_cdev() call the universal interface 'device_register',
which can return error when kzalloc fail, or sysfs error, etc.

Hope the above information is helpful.

------
Best regards
Wang Liang

>
> Otherwise, makes perfect sense to me. I'm new to this code, so grain of
> salt, but since I exposed it:
>
> Reviewed-by: Calvin Owens <calvin@wbinvd.org>
>
> Thanks,
> Calvin
>
>> Fixes: c79a39dc8d06 ("pps: Fix a use-after-free")
>> Signed-off-by: Wang Liang <wangliang74@huawei.com>
>> ---
>>   drivers/pps/pps.c | 4 +---
>>   1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
>> index 9463232af8d2..0d2d57250575 100644
>> --- a/drivers/pps/pps.c
>> +++ b/drivers/pps/pps.c
>> @@ -383,13 +383,11 @@ int pps_register_cdev(struct pps_device *pps)
>>   	pps->dev.devt = MKDEV(pps_major, pps->id);
>>   	dev_set_drvdata(&pps->dev, pps);
>>   	dev_set_name(&pps->dev, "pps%d", pps->id);
>> +	pps->dev.release = pps_device_destruct;
>>   	err = device_register(&pps->dev);
>>   	if (err)
>>   		goto free_idr;
>>   
>> -	/* Override the release function with our own */
>> -	pps->dev.release = pps_device_destruct;
>> -
>>   	pr_debug("source %s got cdev (%d:%d)\n", pps->info.name, pps_major,
>>   		 pps->id);
>>   
>> -- 
>> 2.33.0
>>