[PATCH 0/2] mtd: use put_device() if device_register fail

[PATCH 0/2] mtd: use put_device() if device_register fail

[Arvind Yadav]

if device_register() returned an error! Always use put_device()
to give up the reference initialized.

Arvind Yadav (2):
  [PATCH 1/2] mtd: use put_device() if device_register fail
  [PATCH 2/2] mtd: ubi: use put_device() if device_register fail

 drivers/mtd/mtdcore.c | 1 +
 drivers/mtd/ubi/vmt.c | 1 +
 2 files changed, 2 insertions(+)

-- 
1.9.1

[PATCH 1/2] mtd: use put_device() if device_register fail

[Arvind Yadav]

if device_register() returned an error! Always use put_device()
to give up the reference initialized.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
---
 drivers/mtd/mtdcore.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 28553c8..4d77ca2 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -586,6 +586,7 @@ int add_mtd_device(struct mtd_info *mtd)
 	return 0;
 
 fail_added:
+	put_device(&mtd->dev);
 	of_node_put(mtd_get_of_node(mtd));
 	idr_remove(&mtd_idr, i);
 fail_locked:
-- 
1.9.1

[PATCH 2/2] mtd: ubi: use put_device() if device_register fail

[Arvind Yadav]

if device_register() returned an error! Always use put_device()
to give up the reference initialized.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
---
 drivers/mtd/ubi/vmt.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/mtd/ubi/vmt.c b/drivers/mtd/ubi/vmt.c
index 3fd8d7f..db85b68 100644
--- a/drivers/mtd/ubi/vmt.c
+++ b/drivers/mtd/ubi/vmt.c
@@ -609,6 +609,7 @@ int ubi_add_volume(struct ubi_device *ubi, struct ubi_volume *vol)
 	return err;
 
 out_cdev:
+	put_device(&vol->dev);
 	cdev_del(&vol->cdev);
 	return err;
 }
-- 
1.9.1

Re: [PATCH 0/2] mtd: use put_device() if device_register fail

[Richard Weinberger]

Am Freitag, 9. März 2018, 11:50:47 CET schrieb Arvind Yadav:
> if device_register() returned an error! Always use put_device()
> to give up the reference initialized.
> 
> Arvind Yadav (2):
>   [PATCH 1/2] mtd: use put_device() if device_register fail
>   [PATCH 2/2] mtd: ubi: use put_device() if device_register fail

Uhh, this is not obvious. Does device_register() really always return with a 
reference held in all (error) cases?

Thanks,
//richard

Re: [PATCH 0/2] mtd: use put_device() if device_register fail

[Arvind Yadav]

On Monday 12 March 2018 01:05 AM, Richard Weinberger wrote:
> Am Freitag, 9. März 2018, 11:50:47 CET schrieb Arvind Yadav:
>> if device_register() returned an error! Always use put_device()
>> to give up the reference initialized.
>>
>> Arvind Yadav (2):
>>    [PATCH 1/2] mtd: use put_device() if device_register fail
>>    [PATCH 2/2] mtd: ubi: use put_device() if device_register fail
> Uhh, this is not obvious. Does device_register() really always return with a
> reference held in all (error) cases?
>
> Thanks,
> //richard
if device_register() returned an error! Always use put_device()
to give up the reference initialized.(-- Please see the comment
for device_register() ). put_device() is able to handle those case
where it'll not return a reference.

~arvind

Re: [PATCH 0/2] mtd: use put_device() if device_register fail

[Richard Weinberger]

Arvind,

Am Montag, 12. März 2018, 06:51:24 CET schrieb Arvind Yadav:
> On Monday 12 March 2018 01:05 AM, Richard Weinberger wrote:
> > Am Freitag, 9. März 2018, 11:50:47 CET schrieb Arvind Yadav:
> >> if device_register() returned an error! Always use put_device()
> >> to give up the reference initialized.
> >> 
> >> Arvind Yadav (2):
> >>    [PATCH 1/2] mtd: use put_device() if device_register fail
> >>    [PATCH 2/2] mtd: ubi: use put_device() if device_register fail
> > 
> > Uhh, this is not obvious. Does device_register() really always return with
> > a reference held in all (error) cases?
> > 
> > Thanks,
> > //richard
> 
> if device_register() returned an error! Always use put_device()
> to give up the reference initialized.(-- Please see the comment
> for device_register() ). put_device() is able to handle those case
> where it'll not return a reference.

You are right.

For both patches:
Acked-by: Richard Weinberger <richard@nod.at>

Thanks,
//richard

Re: [PATCH 1/2] mtd: use put_device() if device_register fail

[Boris Brezillon]

On Fri,  9 Mar 2018 16:20:48 +0530
Arvind Yadav <arvind.yadav.cs@gmail.com> wrote:

> if device_register() returned an error! Always use put_device()
> to give up the reference initialized.
> 
> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
> ---
>  drivers/mtd/mtdcore.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 28553c8..4d77ca2 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -586,6 +586,7 @@ int add_mtd_device(struct mtd_info *mtd)
>  	return 0;
>  
>  fail_added:
> +	put_device(&mtd->dev);

Not sure this is a good idea: the put_device() call will trigger
an mtd_devtype->release(), which will in turn call device_destroy() on
something that does not exist yet. Not sure if this is a real problem,
but it does not look like the right thing to do.

>  	of_node_put(mtd_get_of_node(mtd));

You're referencing an object that is supposed to have been
freed/released by the put_device() call. Again, it's not really a
problem because in our case ->release() does not free the mtd object
(as is usually done in other parts of the kernel), but it still looks
wrong. It's probably better to move the of_node_put() and the below
idr_remove() call in the ->release() hook if you want to use
put_device().

>  	idr_remove(&mtd_idr, i);



>  fail_locked:



-- 
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH 2/2] mtd: ubi: use put_device() if device_register fail

[Boris Brezillon]

On Fri,  9 Mar 2018 16:20:49 +0530
Arvind Yadav <arvind.yadav.cs@gmail.com> wrote:

> if device_register() returned an error! Always use put_device()
> to give up the reference initialized.
> 
> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
> ---
>  drivers/mtd/ubi/vmt.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/mtd/ubi/vmt.c b/drivers/mtd/ubi/vmt.c
> index 3fd8d7f..db85b68 100644
> --- a/drivers/mtd/ubi/vmt.c
> +++ b/drivers/mtd/ubi/vmt.c
> @@ -609,6 +609,7 @@ int ubi_add_volume(struct ubi_device *ubi, struct ubi_volume *vol)
>  	return err;
>  
>  out_cdev:
> +	put_device(&vol->dev);
>  	cdev_del(&vol->cdev);

use-after-free bug here: put_device() has freed the vol obj, and you're
dereferencing the pointer just after that.

>  	return err;
>  }



-- 
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH 2/2] mtd: ubi: use put_device() if device_register fail

[Richard Weinberger]

Am Mittwoch, 14. März 2018, 19:56:52 CET schrieb Boris Brezillon:
> On Fri,  9 Mar 2018 16:20:49 +0530
> 
> Arvind Yadav <arvind.yadav.cs@gmail.com> wrote:
> > if device_register() returned an error! Always use put_device()
> > to give up the reference initialized.
> > 
> > Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
> > ---
> > 
> >  drivers/mtd/ubi/vmt.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/mtd/ubi/vmt.c b/drivers/mtd/ubi/vmt.c
> > index 3fd8d7f..db85b68 100644
> > --- a/drivers/mtd/ubi/vmt.c
> > +++ b/drivers/mtd/ubi/vmt.c
> > @@ -609,6 +609,7 @@ int ubi_add_volume(struct ubi_device *ubi, struct
> > ubi_volume *vol)> 
> >  	return err;
> >  
> >  out_cdev:
> > +	put_device(&vol->dev);
> > 
> >  	cdev_del(&vol->cdev);
> 
> use-after-free bug here: put_device() has freed the vol obj, and you're
> dereferencing the pointer just after that.

eeek, thanks for looking at more context.
Arvind, while you are right that put_device() is missing, please double check 
that freeing the devices is also correct.

Thanks,
//richard

Re: [PATCH 2/2] mtd: ubi: use put_device() if device_register fail

[Arvind Yadav]

On Thursday 15 March 2018 12:55 AM, Richard Weinberger wrote:
> Am Mittwoch, 14. März 2018, 19:56:52 CET schrieb Boris Brezillon:
>> On Fri,  9 Mar 2018 16:20:49 +0530
>>
>> Arvind Yadav <arvind.yadav.cs@gmail.com> wrote:
>>> if device_register() returned an error! Always use put_device()
>>> to give up the reference initialized.
>>>
>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
>>> ---
>>>
>>>   drivers/mtd/ubi/vmt.c | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/mtd/ubi/vmt.c b/drivers/mtd/ubi/vmt.c
>>> index 3fd8d7f..db85b68 100644
>>> --- a/drivers/mtd/ubi/vmt.c
>>> +++ b/drivers/mtd/ubi/vmt.c
>>> @@ -609,6 +609,7 @@ int ubi_add_volume(struct ubi_device *ubi, struct
>>> ubi_volume *vol)>
>>>   	return err;
>>>   
>>>   out_cdev:
>>> +	put_device(&vol->dev);
>>>
>>>   	cdev_del(&vol->cdev);
>> use-after-free bug here: put_device() has freed the vol obj, and you're
>> dereferencing the pointer just after that.
Thanks Boris, to point out this error.
> eeek, thanks for looking at more context.
> Arvind, while you are right that put_device() is missing, please double check
> that freeing the devices is also correct.
>
> Thanks,
> //richard
Sorry for that. I will take care of this.

~arvind

Re: [PATCH 1/2] mtd: use put_device() if device_register fail

[arvindY]

On Wednesday 14 March 2018 08:06 PM, Boris Brezillon wrote:
> On Fri,  9 Mar 2018 16:20:48 +0530
> Arvind Yadav <arvind.yadav.cs@gmail.com> wrote:
>
>> if device_register() returned an error! Always use put_device()
>> to give up the reference initialized.
>>
>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
>> ---
>>   drivers/mtd/mtdcore.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
>> index 28553c8..4d77ca2 100644
>> --- a/drivers/mtd/mtdcore.c
>> +++ b/drivers/mtd/mtdcore.c
>> @@ -586,6 +586,7 @@ int add_mtd_device(struct mtd_info *mtd)
>>   	return 0;
>>   
>>   fail_added:
>> +	put_device(&mtd->dev);
> Not sure this is a good idea: the put_device() call will trigger
> an mtd_devtype->release(), which will in turn call device_destroy() on
> something that does not exist yet. Not sure if this is a real problem,
> but it does not look like the right thing to do.
>
yes, you are correct. No need to call put_device().
which can cause other problem.

>>   	of_node_put(mtd_get_of_node(mtd));
> You're referencing an object that is supposed to have been
> freed/released by the put_device() call. Again, it's not really a
> problem because in our case ->release() does not free the mtd object
> (as is usually done in other parts of the kernel), but it still looks
> wrong. It's probably better to move the of_node_put() and the below
> idr_remove() call in the ->release() hook if you want to use
> put_device().
>
>>   	idr_remove(&mtd_idr, i);
Sure, we can move put_device() below this. But need to check
how we can add hook in release.
>
>>   fail_locked:
>
>
~arvind