[PATCH] rtlwifi: get buffer_desc before trying to alloc new skb

if rtlpriv->use_new_trx_flow == true and we run out of memory
to alloc a new skb, we will directly jump to no_new tag with
buffer_desc == NULL. Then we will dereference this NULL pointer
in function _rtl_pci_init_one_rxdesc.

Signed-off-by: Yang Bai <redacted>
---
 drivers/net/wireless/rtlwifi/pci.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/rtlwifi/pci.c b/drivers/net/wireless/rtlwifi/pci.c
index a62170e..7fe04d1 100644
--- a/drivers/net/wireless/rtlwifi/pci.c
+++ b/drivers/net/wireless/rtlwifi/pci.c

@@ -820,17 +820,19 @@ static void _rtl_pci_rx_interrupt(struct ieee80211_hw *hw)
 		pci_unmap_single(rtlpci->pdev, *((dma_addr_t *)skb->cb),
 				 rtlpci->rxbuffersize, PCI_DMA_FROMDEVICE);
 
+		if (rtlpriv->use_new_trx_flow)
+			buffer_desc =
+			  &rtlpci->rx_ring[rxring_idx].buffer_desc
+				[rtlpci->rx_ring[rxring_idx].idx];
+
 		/* get a new skb - if fail, old one will be reused */
 		new_skb = dev_alloc_skb(rtlpci->rxbuffersize);
 		if (unlikely(!new_skb))
 			goto no_new;
-		if (rtlpriv->use_new_trx_flow) {
-			buffer_desc =
-			  &rtlpci->rx_ring[rxring_idx].buffer_desc
-				[rtlpci->rx_ring[rxring_idx].idx];
+		if (rtlpriv->use_new_trx_flow)
 			/*means rx wifi info*/
 			pdesc = (struct rtl_rx_desc *)skb->data;
-		}
+
 		memset(&rx_status , 0 , sizeof(rx_status));
 		rtlpriv->cfg->ops->query_rx_desc(hw, &stats,
 						 &rx_status, (u8 *)pdesc, skb);

-- 
2.3.1

On 03/12/2015 06:33 AM, Yang Bai wrote:

if rtlpriv->use_new_trx_flow == true and we run out of memory
to alloc a new skb, we will directly jump to no_new tag with
buffer_desc == NULL. Then we will dereference this NULL pointer
in function _rtl_pci_init_one_rxdesc.

Signed-off-by: Yang Bai <redacted>

Good catch. The only problem that I have is this fix adds even more branching to 
this interrupt routine. At first glance, I should be able to set buffer_desc in 
the earlier code where the code has already branched. For testing, an RTL8192EE 
card will be needed. Do you have such a card?

Larry

On 03/12/2015 06:33 AM, Yang Bai wrote:

if rtlpriv->use_new_trx_flow == true and we run out of memory
to alloc a new skb, we will directly jump to no_new tag with
buffer_desc == NULL. Then we will dereference this NULL pointer
in function _rtl_pci_init_one_rxdesc.

Signed-off-by: Yang Bai <redacted>

Is the attached patch OK? I have tested it, but it is unlikely that I have hit 
any memory failures, thus that part needs to be checked by eye.

Larry

On Fri, Mar 13, 2015 at 1:29 AM, Larry Finger [off-list ref] wrote:

On 03/12/2015 06:33 AM, Yang Bai wrote:

quoted

if rtlpriv->use_new_trx_flow == true and we run out of memory
to alloc a new skb, we will directly jump to no_new tag with
buffer_desc == NULL. Then we will dereference this NULL pointer
in function _rtl_pci_init_one_rxdesc.

Signed-off-by: Yang Bai <redacted>

Is the attached patch OK? I have tested it, but it is unlikely that I have
hit any memory failures, thus that part needs to be checked by eye.

Looks good to me. Thanks very much for your review.

Yang

Larry

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