rtlwifi: Fix possible NULL dereference

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.

In a separate call to dev_alloc_skb(), the debug level is changed so that
the failure message will always be logged.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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_EMERG,
+							("can't alloc rx skb\n"));
+						goto done;
+					}
 					memcpy(IEEE80211_SKB_RXCB(uskb),
 							&rx_status,
 							sizeof(rx_status));
@@ -641,7 +648,7 @@ static void _rtl_pci_rx_interrupt(struct ieee80211_hw *hw)
 			new_skb = dev_alloc_skb(rtlpci->rxbuffersize);
 			if (unlikely(!new_skb)) {
 				RT_TRACE(rtlpriv, (COMP_INTR | COMP_RECV),
-					 DBG_DMESG,
+					 DBG_EMERG,
 					 ("can't alloc skb for rx\n"));
 				goto done;
 			}
@@ -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; */