linux-kernel - Re: [PATCH] staging: Check against NULL in fw_download

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Date:	Mon, 11 Aug 2014 12:04:38 -0700
From:	Randy Dunlap <rdunlap@...radead.org>
To:	Nick Krause <xerofoify@...il.com>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	lisa@...apiadmin.com, Ben Hutchings <ben@...adent.org.uk>,
	Valentina Manea <valentina.manea.m@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: Check against NULL in fw_download_code

On 08/11/14 11:55, Nick Krause wrote:
> On Mon, Aug 11, 2014 at 2:45 PM, Randy Dunlap <rdunlap@...radead.org> wrote:
>> On 08/11/14 11:26, Nick Krause wrote:
>>> On Mon, Aug 11, 2014 at 2:07 PM, Randy Dunlap <rdunlap@...radead.org> wrote:
>>>> On 08/11/14 11:04, Nick Krause wrote:
>>>>> On Mon, Aug 11, 2014 at 2:02 PM, Nicholas Krause <xerofoify@...il.com> wrote:
>>>>>> I am fixing the bug entry , https://bugzilla.kernel.org/show_bug.cgi?id=60461.
>>>>>> This entry states that we are not checking the skb allocated in fw_download_code
>>>>>> and after checking I fixed it to check for the NULL value before using the allocate
>>>>>> skb.
>>>>>>
>>>>>> Signed-off-by: Nicholas Krause <xerofoify@...il.com>
>>>>>> ---
>>>>>>  drivers/staging/rtl8192e/rtl8192e/r8192E_firmware.c | 14 ++++++++------
>>>>>>  1 file changed, 8 insertions(+), 6 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/staging/rtl8192e/rtl8192e/r8192E_firmware.c b/drivers/staging/rtl8192e/rtl8192e/r8192E_firmware.c
>>>>>> index 1a95d1f..0a4c926 100644
>>>>>> --- a/drivers/staging/rtl8192e/rtl8192e/r8192E_firmware.c
>>>>>> +++ b/drivers/staging/rtl8192e/rtl8192e/r8192E_firmware.c
>>>>>> @@ -60,13 +60,15 @@ static bool fw_download_code(struct net_device *dev, u8 *code_virtual_address,
>>>>>>
>>>>>>                 }
>>>>>>
>>>>>> -               skb  = dev_alloc_skb(frag_length + 4);
>>>>>> -               memcpy((unsigned char *)(skb->cb), &dev, sizeof(dev));
>>>>>> -               tcb_desc = (struct cb_desc *)(skb->cb + MAX_DEV_ADDR_SIZE);
>>>>>> -               tcb_desc->queue_index = TXCMD_QUEUE;
>>>>>> -               tcb_desc->bCmdOrInit = DESC_PACKET_TYPE_INIT;
>>>>>> -               tcb_desc->bLastIniPkt = bLastIniPkt;
>>>>>>
>>>>>> +               skb  = dev_alloc_skb(frag_length + 4);
>>>>>> +               if (skb) {
>>>>>> +                       memcpy((unsigned char *)(skb->cb), &dev, sizeof(dev));
>>>>>> +                       tcb_desc = (struct cb_desc *)(skb->cb + MAX_DEV_ADDR_SIZE);
>>>>>> +                       tcb_desc->queue_index = TXCMD_QUEUE;
>>>>>> +                       tcb_desc->bCmdOrInit = DESC_PACKET_TYPE_INIT;
>>>>>> +                       tcb_desc->bLastIniPkt = bLastIniPkt;
>>>>>> +               }
>>>>
>>>> and what happens here (below) if skb is NULL?
>>
>> Nick,
>> I'm asking if you have completely fixed the bug or only partially fixed it.
>> The answer is that the patch is only a partial fix.  If skb is NULL, there
>> is still a problem in the statement below here.  The kernel will oops on
>> that reference to skb, which is NULL.
>>
>>>>
>>>>>>                 seg_ptr = skb->data;
>>>>>>                 for (i = 0; i < frag_length; i += 4) {
>>>>>>                         *seg_ptr++ = ((i+0) < frag_length) ?
>>>>>> --
>>>>>> 1.9.1
>>>>>>
>>>>> And I did check it against Linus's tree to make sure it applies , just
>>>>> to let you known.
>>>>> Nick
>>>>
>>>>
>>>> --
>>>> ~Randy
>>> Sorry Randy.
>>>  I may be mis reading this, but are you asking me to write a different
>>> commit message or is this patch just another bad patch in my series of
>>> bad patches?
>>
>>
>> --
>> ~Randy
> 
> Randy ,
> Thanks for the catch :). Would you recommend just putting it in the if
> statement I created or create a second if statement for
> code readability.

Neither one of those choices.  I suggest that the code immediately check for
skb == NULL and return 0 (or false) if it is NULL.  Then the code below that check
won't need to be changed at all.



-- 
~Randy
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