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

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

[Wang Liang]

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 Now the comment is outdated,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.

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

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

[Calvin Owens]

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?

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
> 

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

[Wang Liang]

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
>>

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

[Calvin Owens]

On Thursday 08/28 at 17:24 +0800, Wang Liang wrote:
> 
> 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.

Thanks Wang, no worries, I just noticed it was under TIOCSETD and
thought syzcaller might've lucked into something interesting there too.

> ------
> 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
> > > 

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

[Calvin Owens]

On Wednesday 08/27 at 08:32 -0700, Calvin Owens wrote:
> 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?
> 
> 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>

I apologize Wang, I missed something when I looked at this yesterday:

I think your patch introduces a double-free, because the pps object is
already freed by pps_register_source() when pps_register_cdev() returns
an error. Because put_device() was a nop with the missing release_fn, it
wasn't actually doing anything. That's very confusing, and my fault.

Your patch is clearly an improvement. But I think you additionally need
to remove the 'kfree_pps' error logic at the bottom of
pps_register_source() to avoid a double free in the failure case:

diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
index 92d1b62ea239..4d0ba35590a3 100644
--- a/drivers/pps/kapi.c
+++ b/drivers/pps/kapi.c
@@ -116,9 +116,6 @@ struct pps_device *pps_register_source(struct pps_source_info *info,
 
 	return pps;
 
-kfree_pps:
-	kfree(pps);
-
 pps_register_source_exit:
 	pr_err("%s: unable to register source\n", info->name);
 

The only reason I put that kfree() there is because I noticed the memory
was being leaked in the failure case. Doh. Your patch makes this right.

> 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
> > 

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

[Wang Liang]

在 2025/8/28 21:24, Calvin Owens 写道:
> On Wednesday 08/27 at 08:32 -0700, Calvin Owens wrote:
>> 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?
>>
>> 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>
> I apologize Wang, I missed something when I looked at this yesterday:
>
> I think your patch introduces a double-free, because the pps object is
> already freed by pps_register_source() when pps_register_cdev() returns
> an error. Because put_device() was a nop with the missing release_fn, it
> wasn't actually doing anything. That's very confusing, and my fault.


You are right! Thanks for the reminder. I reproduce the double-free issue:

==================================================================
BUG: KASAN: double-free in pps_register_source+0x2c1/0x3a0
Free of addr ffff8881078fd800 by task insmod/323
Call Trace:
  <TASK>
  dump_stack_lvl+0x55/0x70
  print_report+0xcb/0x610
  kasan_report_invalid_free+0x94/0xc0
  check_slab_allocation+0x105/0x130
  kfree+0xba/0x360
  pps_register_source+0x2c1/0x3a0

It is triggered by kzalloc fail in device_private_init().

> Your patch is clearly an improvement. But I think you additionally need
> to remove the 'kfree_pps' error logic at the bottom of
> pps_register_source() to avoid a double free in the failure case:


Thanks for your suggestions, it is helpful!

I will send a v2 patch later. Thanks!

------
Best regards
Wang Liang

>
> diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
> index 92d1b62ea239..4d0ba35590a3 100644
> --- a/drivers/pps/kapi.c
> +++ b/drivers/pps/kapi.c
> @@ -116,9 +116,6 @@ struct pps_device *pps_register_source(struct pps_source_info *info,
>   
>   	return pps;
>   
> -kfree_pps:
> -	kfree(pps);
> -
>   pps_register_source_exit:
>   	pr_err("%s: unable to register source\n", info->name);
>   
>
> The only reason I put that kfree() there is because I noticed the memory
> was being leaked in the failure case. Doh. Your patch makes this right.
>
>> 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
>>>