linux-kernel - Re: [PATCH] mwifiex: fix possible NULL dereference

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Date:	Tue, 12 Apr 2016 17:43:03 +0000
From:	"Rustad, Mark D" <mark.d.rustad@...el.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
CC:	Sudip Mukherjee <sudipm.mukherjee@...il.com>,
	Amitkumar Karwar <akarwar@...vell.com>,
	Nishant Sarmukadam <nishants@...vell.com>,
	Kalle Valo <kvalo@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"open list:TI WILINK WIRELES..." <linux-wireless@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	"Sudip Mukherjee" <sudip.mukherjee@...ethink.co.uk>
Subject: Re: [PATCH] mwifiex: fix possible NULL dereference

Andy Shevchenko <andy.shevchenko@...il.com> wrote:

> On Mon, Apr 11, 2016 at 6:27 PM, Sudip Mukherjee
> <sudipm.mukherjee@...il.com> wrote:
>> From: Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>
>>
>> We have a check for card just after dereferencing it. So if it is NULL
>> we have already dereferenced it before its check. Lets dereference it
>> after checking card for NULL.
>
> IIUC the code does nothing with dereference.
>
> I would have told NAK if I would have been maintainer.
>
>> Signed-off-by: Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>
>> ---
>>  drivers/net/wireless/marvell/mwifiex/pcie.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/wireless/marvell/mwifiex/pcie.c  
>> b/drivers/net/wireless/marvell/mwifiex/pcie.c
>> index edf8b07..84562d0 100644
>> --- a/drivers/net/wireless/marvell/mwifiex/pcie.c
>> +++ b/drivers/net/wireless/marvell/mwifiex/pcie.c
>> @@ -2884,10 +2884,11 @@ static void mwifiex_unregister_dev(struct  
>> mwifiex_adapter *adapter)
>>  {
>>         struct pcie_service_card *card = adapter->card;
>
> Let's say it's 0.
>
>>        const struct mwifiex_pcie_card_reg *reg;
>> -       struct pci_dev *pdev = card->dev;
>
> This would be equal to offset of dev member in pcie_service_card struct.
>
> Nothing wrong here.

Actually, that is not true. The dereference of card tells the compiler that  
card can't be NULL, so it is free to eliminate the check below.  
Unbelievably, this can even happen for a reference such as &ptr->thing  
where the pointer isn't even actually dereferenced at all!

>> +       struct pci_dev *pdev;
>>         int i;
>>
>>         if (card) {
>> +               pdev = card->dev;
>>                 if (card->msix_enable) {
>>                         for (i = 0; i < MWIFIEX_NUM_MSIX_VECTORS; i++)
>>                                 synchronize_irq(card->msix_entries[i].vector);
>> --
>> 1.9.1
>
>
>
> --
> With Best Regards,
> Andy Shevchenko


--
Mark Rustad, Networking Division, Intel Corporation

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