linux-kernel - Re: [PATCHv3] mvsas:Fix possible NULL pointer deference in mvs_dev_found

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Date:	Sun, 03 Jul 2016 14:54:01 +0100
From:	Luis de Bethencourt <luisbg@....samsung.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Nicholas Krause <xerofoify@...il.com>
CC:	"Martin K. Petersen" <martin.petersen@...cle.com>, tj@...nel.org,
	hare@...e.de, jthumshirn@...e.de, Wilfried.Weissmann@....de,
	davispuh@...il.com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3] mvsas:Fix possible NULL pointer deference in mvs_dev_found_notify

On 02/07/16 20:05, James Bottomley wrote:
> On Sat, 2016-07-02 at 19:16 +0100, Luis de Bethencourt wrote:
>> On 02/07/16 18:00, Nicholas Krause wrote:
>>> This adds properly checking after the call to mvs_find_dev_mvi
>>>  due to this function being able to return a NULL pointer and
>>> if this does arise we will deference it in mvs_alloc_dev due
>>> to this function never checking if a NULL pointer is given as
>>> it's input argument. Signed-off-by: Nicholas Krause <
>>> xerofoify@...il.com>
>>> ---
>>> v3 - Make logic simpler on error path by returning -1 directly
>>> if mvs_find_dev_mvi returns NULL.
>>> v2 - Fix NULL pointer deferenece in error path by calling 
>>> spin_unlock_irqrestore on the now NULL pointer, as returned
>>>
>>>
>>>  drivers/scsi/mvsas/mv_sas.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/scsi/mvsas/mv_sas.c
>>> b/drivers/scsi/mvsas/mv_sas.c
>>> index 5b9fcff..dffab01 100644
>>> --- a/drivers/scsi/mvsas/mv_sas.c
>>> +++ b/drivers/scsi/mvsas/mv_sas.c
>>> @@ -1194,6 +1194,8 @@ int mvs_dev_found_notify(struct domain_device
>>> *dev, int lock)
>>>  	struct mvs_device *mvi_device;
>>>  
>>>  	mvi = mvs_find_dev_mvi(dev);
>>> +	if (!mvi)
>>> +		return -1;
>>>  
>>>  	if (lock)
>>>  		spin_lock_irqsave(&mvi->lock, flags);
>>>
>>
>> This looks better :)
>>
>> Checking the value of mvi makes sense if mvs_find_dev_mvi() can
>> return NULL.
> 
> Which it can't, if you actually look at the function.  For this to
> happen, we'd have to be receiving a discovery event for a non-existent
> port on the adapter, meaning the system was so corrupted that operation
> shouldn't be continuing.
> 
> Nick is a known bogus patch submitter.  If you want to review them,
> that's your choice (and perhaps some might be useful), but it's not
> unreasonable of me to expect the review will be thorough enough to turn
> up issues like this.
> 
> James

I had my suspicions about mvfs_find_dev_mvi() returning NULL. Which is why
I said "if it can return NULL". Unfortunately I assumed the base of the patch
was properly considered, because I didn't knew about Nick.

I just searched around and now understand what you mean about his bogus
patches.

Sorry I wasn't thorough enough on my review, I know the above isn't an
excuse. Lesson learned.

In a related note, why is mvi initialized to NULL in mvfs_find_dev_mvi() if
it is going to be overwritten? Curious.

Thanks and apologies,
Luis

> 
> 
>> Reviewed-by: Luis de Bethencourt <luisbg@....samsung.com>
>>
>> Thanks,
>> Luis
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