[PATCH] staging: comedi: (regression) channel list must be set for COMEDI_CMD ioctl

[PATCH] staging: comedi: (regression) channel list must be set for COMEDI_CMD ioctl

[Ian Abbott]

`do_cmd_ioctl()`, the handler for the `COMEDI_CMD` ioctl can incorrectly
call the Comedi subdevice's `do_cmd()` handler with a NULL channel list
pointer.  This is a regression as the `do_cmd()` handler has never been
expected to deal with that, leading to a kernel OOPS when it tries to
dereference it.

A NULL channel list pointer is allowed for the `COMEDI_CMDTEST` ioctl,
handled by `do_cmdtest_ioctl()` and the subdevice's `do_cmdtest()`
handler, but not for the `COMEDI_CMD` ioctl and its handlers.

Both `do_cmd_ioctl()` and `do_cmdtest_ioctl()` call
`__comedi_get_user_chanlist()` to copy the channel list from user memory
into dynamically allocated kernel memory and check it for consistency.
That function currently returns 0 if the `user_chanlist` parameter
(pointing to the channel list in user memory) is NULL.  That's fine for
`do_cmdtest_ioctl()`, but `do_cmd_ioctl()` incorrectly assumes the
kernel copy of the channel list has been set-up correctly.

Fix it by not allowing the `user_chanlist` parameter to be NULL in
`__comedi_get_user_chanlist()`, and only calling it from
`do_cmdtest_ioctl()` if the parameter is non-NULL.

Thanks to Bernd Porr for reporting the bug via an initial patch sent
privately.

Fixes: c6cd0eefb27b ("staging: comedi: comedi_fops: introduce __comedi_get_user_chanlist()")
Reported-by: Bernd Porr <mail@berndporr.me.uk>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Cc: Bernd Porr <mail@berndporr.me.uk>
Cc: <stable@vger.kernel.org> # 3.15.y 3.16.y 3.17.y
---
 drivers/staging/comedi/comedi_fops.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 495969f..a9b7fe5 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1462,10 +1462,6 @@ static int __comedi_get_user_chanlist(struct comedi_device *dev,
 	unsigned int *chanlist;
 	int ret;
 
-	/* user_chanlist could be NULL for do_cmdtest ioctls */
-	if (!user_chanlist)
-		return 0;
-
 	chanlist = memdup_user(user_chanlist,
 			       cmd->chanlist_len * sizeof(unsigned int));
 	if (IS_ERR(chanlist))
@@ -1609,10 +1605,13 @@ static int do_cmdtest_ioctl(struct comedi_device *dev,
 
 	s = &dev->subdevices[cmd.subdev];
 
-	/* load channel/gain list */
-	ret = __comedi_get_user_chanlist(dev, s, user_chanlist, &cmd);
-	if (ret)
-		return ret;
+	/* user_chanlist can be NULL for COMEDI_CMDTEST ioctl */
+	if (user_chanlist) {
+		/* load channel/gain list */
+		ret = __comedi_get_user_chanlist(dev, s, user_chanlist, &cmd);
+		if (ret)
+			return ret;
+	}
 
 	ret = s->do_cmdtest(dev, s, &cmd);
 
-- 
2.1.1

RE: [PATCH] staging: comedi: (regression) channel list must be set for COMEDI_CMD ioctl

[Hartley Sweeten]

On Wednesday, October 08, 2014 8:09 AM, Ian Abbott wrote:
> `do_cmd_ioctl()`, the handler for the `COMEDI_CMD` ioctl can incorrectly
> call the Comedi subdevice's `do_cmd()` handler with a NULL channel list
> pointer.  This is a regression as the `do_cmd()` handler has never been
> expected to deal with that, leading to a kernel OOPS when it tries to
> dereference it.
>
> A NULL channel list pointer is allowed for the `COMEDI_CMDTEST` ioctl,
> handled by `do_cmdtest_ioctl()` and the subdevice's `do_cmdtest()`
> handler, but not for the `COMEDI_CMD` ioctl and its handlers.
>
> Both `do_cmd_ioctl()` and `do_cmdtest_ioctl()` call
> `__comedi_get_user_chanlist()` to copy the channel list from user memory
> into dynamically allocated kernel memory and check it for consistency.
> That function currently returns 0 if the `user_chanlist` parameter
> (pointing to the channel list in user memory) is NULL.  That's fine for
> `do_cmdtest_ioctl()`, but `do_cmd_ioctl()` incorrectly assumes the
> kernel copy of the channel list has been set-up correctly.
>
> Fix it by not allowing the `user_chanlist` parameter to be NULL in
> `__comedi_get_user_chanlist()`, and only calling it from
> `do_cmdtest_ioctl()` if the parameter is non-NULL.
>
> Thanks to Bernd Porr for reporting the bug via an initial patch sent
> privately.
>
> Fixes: c6cd0eefb27b ("staging: comedi: comedi_fops: introduce __comedi_get_user_chanlist()")
> Reported-by: Bernd Porr <mail@berndporr.me.uk>
> Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
> Cc: Bernd Porr <mail@berndporr.me.uk>
> Cc: <stable@vger.kernel.org> # 3.15.y 3.16.y 3.17.y
> ---
>  drivers/staging/comedi/comedi_fops.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
> index 495969f..a9b7fe5 100644
> --- a/drivers/staging/comedi/comedi_fops.c
> +++ b/drivers/staging/comedi/comedi_fops.c
> @@ -1462,10 +1462,6 @@ static int __comedi_get_user_chanlist(struct comedi_device *dev,
>  	unsigned int *chanlist;
>  	int ret;
>  
> -	/* user_chanlist could be NULL for do_cmdtest ioctls */
> -	if (!user_chanlist)
> -		return 0;
> -

I think you need a check here to avoid a NULL pointer getting
passed to the  memdup_user().

	If (!user_chanlist || cmd->chanlist_len == 0)
		return -EINVAL;

>  	chanlist = memdup_user(user_chanlist,
>  			       cmd->chanlist_len * sizeof(unsigned int));
>  	if (IS_ERR(chanlist))
> @@ -1609,10 +1605,13 @@ static int do_cmdtest_ioctl(struct comedi_device *dev,
>  
>  	s = &dev->subdevices[cmd.subdev];
>  
> -	/* load channel/gain list */
> -	ret = __comedi_get_user_chanlist(dev, s, user_chanlist, &cmd);
> -	if (ret)
> -		return ret;
> +	/* user_chanlist can be NULL for COMEDI_CMDTEST ioctl */
> +	if (user_chanlist) {
> +		/* load channel/gain list */
> +		ret = __comedi_get_user_chanlist(dev, s, user_chanlist, &cmd);
> +		if (ret)
> +			return ret;
> +	}
>
>  	ret = s->do_cmdtest(dev, s, &cmd);
 
The reset looks ok.


Side-note on mem_dupuser(). That function does a kmalloc to copy the
user data to the kernel. Shouldn't we be freeing it when we are done with
it?

do_become_nonbusy() does a kfree(async->cmd.chanlist) which will free
the memory for do_cmd_ioctl().

But, do_cmdtest_ioctl() actually copies the user data into a local variable.
I think we are missing a kfree() there.

Regards,
Hartley

Re: [PATCH] staging: comedi: (regression) channel list must be set for COMEDI_CMD ioctl

[Ian Abbott]

On 09/10/14 00:13, Hartley Sweeten wrote:
> On Wednesday, October 08, 2014 8:09 AM, Ian Abbott wrote:
>> `do_cmd_ioctl()`, the handler for the `COMEDI_CMD` ioctl can incorrectly
>> call the Comedi subdevice's `do_cmd()` handler with a NULL channel list
>> pointer.  This is a regression as the `do_cmd()` handler has never been
>> expected to deal with that, leading to a kernel OOPS when it tries to
>> dereference it.
>>
>> A NULL channel list pointer is allowed for the `COMEDI_CMDTEST` ioctl,
>> handled by `do_cmdtest_ioctl()` and the subdevice's `do_cmdtest()`
>> handler, but not for the `COMEDI_CMD` ioctl and its handlers.
>>
>> Both `do_cmd_ioctl()` and `do_cmdtest_ioctl()` call
>> `__comedi_get_user_chanlist()` to copy the channel list from user memory
>> into dynamically allocated kernel memory and check it for consistency.
>> That function currently returns 0 if the `user_chanlist` parameter
>> (pointing to the channel list in user memory) is NULL.  That's fine for
>> `do_cmdtest_ioctl()`, but `do_cmd_ioctl()` incorrectly assumes the
>> kernel copy of the channel list has been set-up correctly.
>>
>> Fix it by not allowing the `user_chanlist` parameter to be NULL in
>> `__comedi_get_user_chanlist()`, and only calling it from
>> `do_cmdtest_ioctl()` if the parameter is non-NULL.
>>
>> Thanks to Bernd Porr for reporting the bug via an initial patch sent
>> privately.
>>
>> Fixes: c6cd0eefb27b ("staging: comedi: comedi_fops: introduce __comedi_get_user_chanlist()")
>> Reported-by: Bernd Porr <mail@berndporr.me.uk>
>> Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
>> Cc: Bernd Porr <mail@berndporr.me.uk>
>> Cc: <stable@vger.kernel.org> # 3.15.y 3.16.y 3.17.y
>> ---
>>   drivers/staging/comedi/comedi_fops.c | 15 +++++++--------
>>   1 file changed, 7 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
>> index 495969f..a9b7fe5 100644
>> --- a/drivers/staging/comedi/comedi_fops.c
>> +++ b/drivers/staging/comedi/comedi_fops.c
>> @@ -1462,10 +1462,6 @@ static int __comedi_get_user_chanlist(struct comedi_device *dev,
>>   	unsigned int *chanlist;
>>   	int ret;
>>
>> -	/* user_chanlist could be NULL for do_cmdtest ioctls */
>> -	if (!user_chanlist)
>> -		return 0;
>> -
>
> I think you need a check here to avoid a NULL pointer getting
> passed to the  memdup_user().
>
> 	If (!user_chanlist || cmd->chanlist_len == 0)
> 		return -EINVAL;
>
>>   	chanlist = memdup_user(user_chanlist,
>>   			       cmd->chanlist_len * sizeof(unsigned int));
>>   	if (IS_ERR(chanlist))

It's fine to pass a NULL pointer to memdup_user().  It won't succeed 
(returning ERR_PTR(-EFAULT)), but it's fine.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@mev.co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-

RE: [PATCH] staging: comedi: (regression) channel list must be set for COMEDI_CMD ioctl

[Hartley Sweeten]

On Thursday, October 09, 2014 2:03 AM, Ian Abbott wrote:
> On 09/10/14 00:13, Hartley Sweeten wrote:
>> On Wednesday, October 08, 2014 8:09 AM, Ian Abbott wrote:
>>> `do_cmd_ioctl()`, the handler for the `COMEDI_CMD` ioctl can incorrectly
>>> call the Comedi subdevice's `do_cmd()` handler with a NULL channel list
>>> pointer.  This is a regression as the `do_cmd()` handler has never been
>>> expected to deal with that, leading to a kernel OOPS when it tries to
>>> dereference it.
>>>
>>> A NULL channel list pointer is allowed for the `COMEDI_CMDTEST` ioctl,
>>> handled by `do_cmdtest_ioctl()` and the subdevice's `do_cmdtest()`
>>> handler, but not for the `COMEDI_CMD` ioctl and its handlers.
>>>
>>> Both `do_cmd_ioctl()` and `do_cmdtest_ioctl()` call
>>> `__comedi_get_user_chanlist()` to copy the channel list from user memory
>>> into dynamically allocated kernel memory and check it for consistency.
>>> That function currently returns 0 if the `user_chanlist` parameter
>>> (pointing to the channel list in user memory) is NULL.  That's fine for
>>> `do_cmdtest_ioctl()`, but `do_cmd_ioctl()` incorrectly assumes the
>>> kernel copy of the channel list has been set-up correctly.
>>>
>>> Fix it by not allowing the `user_chanlist` parameter to be NULL in
>>> `__comedi_get_user_chanlist()`, and only calling it from
>>> `do_cmdtest_ioctl()` if the parameter is non-NULL.
>>>
>>> Thanks to Bernd Porr for reporting the bug via an initial patch sent
>>> privately.
>>>
>>> Fixes: c6cd0eefb27b ("staging: comedi: comedi_fops: introduce __comedi_get_user_chanlist()")
>>> Reported-by: Bernd Porr <mail@berndporr.me.uk>
>>> Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
>>> Cc: Bernd Porr <mail@berndporr.me.uk>
>>> Cc: <stable@vger.kernel.org> # 3.15.y 3.16.y 3.17.y
>>> ---
>>>   drivers/staging/comedi/comedi_fops.c | 15 +++++++--------
>>>   1 file changed, 7 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
>>> index 495969f..a9b7fe5 100644
>>> --- a/drivers/staging/comedi/comedi_fops.c
>>> +++ b/drivers/staging/comedi/comedi_fops.c
>>> @@ -1462,10 +1462,6 @@ static int __comedi_get_user_chanlist(struct comedi_device *dev,
>>>   	unsigned int *chanlist;
>>>   	int ret;
>>>
>>> -	/* user_chanlist could be NULL for do_cmdtest ioctls */
>>> -	if (!user_chanlist)
>>> -		return 0;
>>> -
>>
>> I think you need a check here to avoid a NULL pointer getting
>> passed to the  memdup_user().
>>
>> 	If (!user_chanlist || cmd->chanlist_len == 0)
>> 		return -EINVAL;
>>
>>>   	chanlist = memdup_user(user_chanlist,
>>>   			       cmd->chanlist_len * sizeof(unsigned int));
>>>   	if (IS_ERR(chanlist))
>
> It's fine to pass a NULL pointer to memdup_user().  It won't succeed 
>  (returning ERR_PTR(-EFAULT)), but it's fine.

Ah. OK.

Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>