Fix NULL dereference in rtlwifi driver

In drivers/net/wireless/rtlwifi/pci.c::_rtl_pci_rx_interrupt() we call 
dev_alloc_skb(), which may fail and return NULL, but we do not check the 
returned value against NULL before dereferencing the returned pointer. 
This may lead to a NULL pointer dereference which means we'll crash - not 
good.

This patch tries to solve the issue by testing for NULL and bailing out if 
we couldn't allocate a skb. However, I don't know this code well, so I'm 
not sure that jumping to the 'done' label here is the correct action to 
take. Someone more knowledgable about this code than me should definately 
review it before it is applied anywhere.
While I was in the area I also moved an assignment in 
_rtl_pci_init_rx_ring() a bit - if the dev_alloc_skb() call in that 
function fails there's no reason to waste clock cycles assigning to the 
local variable 'entry', we may as well do that after the NULL check and 
potential bail out.

Here's the proposed patch, but please don't take it as much more than a 
bug report. If it happens to be correct, then by all means apply it, but 
I'm not personally making any guarantees.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
 pci.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

  compile tested only, I don't have the hardware to test for real.

On 01/20/2011 04:18 PM, Jesper Juhl wrote:
> In drivers/net/wireless/rtlwifi/pci.c::_rtl_pci_rx_interrupt() we call 
> dev_alloc_skb(), which may fail and return NULL, but we do not check the 
> returned value against NULL before dereferencing the returned pointer. 
> This may lead to a NULL pointer dereference which means we'll crash - not 
> good.
> 
> This patch tries to solve the issue by testing for NULL and bailing out if 
> we couldn't allocate a skb. However, I don't know this code well, so I'm 
> not sure that jumping to the 'done' label here is the correct action to 
> take. Someone more knowledgable about this code than me should definately 
> review it before it is applied anywhere.
> While I was in the area I also moved an assignment in 
> _rtl_pci_init_rx_ring() a bit - if the dev_alloc_skb() call in that 
> function fails there's no reason to waste clock cycles assigning to the 
> local variable 'entry', we may as well do that after the NULL check and 
> potential bail out.
> 
> Here's the proposed patch, but please don't take it as much more than a 
> bug report. If it happens to be correct, then by all means apply it, but 
> I'm not personally making any guarantees.
> 
> Signed-off-by: Jesper Juhl <jj@chaosbits.net>
> ---
>  pci.c |    9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
>   compile tested only, I don't have the hardware to test for real.
> 
> diff --git a/drivers/net/wireless/rtlwifi/pci.c b/drivers/net/wireless/rtlwifi/pci.c
> index 0fa36aa..5e99f89 100644
> --- a/drivers/net/wireless/rtlwifi/pci.c
> +++ b/drivers/net/wireless/rtlwifi/pci.c
> @@ -619,6 +619,13 @@ static void _rtl_pci_rx_interrupt(struct ieee80211_hw *hw)
>  					struct sk_buff *uskb = NULL;
>  					u8 *pdata;
>  					uskb = dev_alloc_skb(skb->len + 128);
> +					if (!uskb) {
> +						RT_TRACE(rtlpriv,
> +							(COMP_INTR | COMP_RECV),
> +							DBG_DMESG,
> +							("can't alloc rx skb\n"));
> +						goto done;
> +					}
>  					memcpy(IEEE80211_SKB_RXCB(uskb),
>  							&rx_status,
>  							sizeof(rx_status));
> @@ -1066,9 +1073,9 @@ static int _rtl_pci_init_rx_ring(struct ieee80211_hw *hw)
>  			struct sk_buff *skb =
>  			    dev_alloc_skb(rtlpci->rxbuffersize);
>  			u32 bufferaddress;
> -			entry = &rtlpci->rx_ring[rx_queue_idx].desc[i];
>  			if (!skb)
>  				return 0;
> +			entry = &rtlpci->rx_ring[rx_queue_idx].desc[i];
>  
>  			/*skb->dev = dev; */
>  

This patch looks mostly good to me. The only change I would make is to replace
"DBG_DMESG" in the RT_TRACE statement with "DBG_EMERG". The standard setting of
the debug variable does not generate output for DBG_DMESG.

With that change, ACK and
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>

Larry

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