[PATCH][net-next] iavf: fix dereference of null rx_buffer pointer

[PATCH][net-next] iavf: fix dereference of null rx_buffer pointer

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

A recent commit efa14c3985828d ("iavf: allow null RX descriptors") added
a null pointer sanity check on rx_buffer, however, rx_buffer is being
dereferenced before that check, which implies a null pointer dereference
bug can potentially occur.  Fix this by only dereferencing rx_buffer
until after the null pointer check.

Addresses-Coverity: ("Dereference before null check")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/net/ethernet/intel/iavf/iavf_txrx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/iavf/iavf_txrx.c b/drivers/net/ethernet/intel/iavf/iavf_txrx.c
index 1cde1601bc32..0cca1b589b56 100644
--- a/drivers/net/ethernet/intel/iavf/iavf_txrx.c
+++ b/drivers/net/ethernet/intel/iavf/iavf_txrx.c
@@ -1296,7 +1296,7 @@ static struct sk_buff *iavf_construct_skb(struct iavf_ring *rx_ring,
 					  struct iavf_rx_buffer *rx_buffer,
 					  unsigned int size)
 {
-	void *va = page_address(rx_buffer->page) + rx_buffer->page_offset;
+	void *va;
 #if (PAGE_SIZE < 8192)
 	unsigned int truesize = iavf_rx_pg_size(rx_ring) / 2;
 #else
@@ -1308,6 +1308,7 @@ static struct sk_buff *iavf_construct_skb(struct iavf_ring *rx_ring,
 	if (!rx_buffer)
 		return NULL;
 	/* prefetch first cache line of first page */
+	va = page_address(rx_buffer->page) + rx_buffer->page_offset;
 	prefetch(va);
 #if L1_CACHE_BYTES < 128
 	prefetch(va + L1_CACHE_BYTES);
@@ -1362,7 +1363,7 @@ static struct sk_buff *iavf_build_skb(struct iavf_ring *rx_ring,
 				      struct iavf_rx_buffer *rx_buffer,
 				      unsigned int size)
 {
-	void *va = page_address(rx_buffer->page) + rx_buffer->page_offset;
+	void *va;
 #if (PAGE_SIZE < 8192)
 	unsigned int truesize = iavf_rx_pg_size(rx_ring) / 2;
 #else
@@ -1374,6 +1375,7 @@ static struct sk_buff *iavf_build_skb(struct iavf_ring *rx_ring,
 	if (!rx_buffer)
 		return NULL;
 	/* prefetch first cache line of first page */
+	va = page_address(rx_buffer->page) + rx_buffer->page_offset;
 	prefetch(va);
 #if L1_CACHE_BYTES < 128
 	prefetch(va + L1_CACHE_BYTES);
-- 
2.20.1

RE: [Intel-wired-lan] [PATCH][net-next] iavf: fix dereference of null rx_buffer pointer

[Bowers, AndrewX]

> -----Original Message-----
> From: Intel-wired-lan [mailto:intel-wired-lan-bounces@osuosl.org] On
> Behalf Of Colin King
> Sent: Wednesday, June 19, 2019 7:31 AM
> To: Kirsher, Jeffrey T <jeffrey.t.kirsher@intel.com>; David S . Miller
> <davem@davemloft.net>; intel-wired-lan@lists.osuosl.org;
> netdev@vger.kernel.org
> Cc: kernel-janitors@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: [Intel-wired-lan] [PATCH][net-next] iavf: fix dereference of null
> rx_buffer pointer
> 
> From: Colin Ian King <colin.king@canonical.com>
> 
> A recent commit efa14c3985828d ("iavf: allow null RX descriptors") added a
> null pointer sanity check on rx_buffer, however, rx_buffer is being
> dereferenced before that check, which implies a null pointer dereference
> bug can potentially occur.  Fix this by only dereferencing rx_buffer until after
> the null pointer check.
> 
> Addresses-Coverity: ("Dereference before null check")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/net/ethernet/intel/iavf/iavf_txrx.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Tested-by: Andrew Bowers <andrewx.bowers@intel.com>