[PATCH 3.16 203/217] sh_eth: fix NULL pointer dereference in sh_eth_ring_format()

[Ben Hutchings]

3.16.35-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx>

[ Upstream commit c1b7fca65070bfadca94dd53a4e6b71cd4f69715 ]

In a low memory situation, if netdev_alloc_skb() fails on a first RX ring
loop iteration  in sh_eth_ring_format(), 'rxdesc' is still NULL.  Avoid
kernel oops by adding the 'rxdesc' check after the loop.

Reported-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/net/ethernet/renesas/sh_eth.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/renesas/sh_eth.c
+++ b/drivers/net/ethernet/renesas/sh_eth.c
@@ -1162,7 +1162,8 @@ static void sh_eth_ring_format(struct ne
 	mdp->dirty_rx = (u32) (i - mdp->num_rx_ring);
 
 	/* Mark the last entry as wrapping the ring. */
-	rxdesc->status |= cpu_to_edmac(mdp, RD_RDEL);
+	if (rxdesc)
+		rxdesc->status |= cpu_to_edmac(mdp, RD_RDEL);
 
 	memset(mdp->tx_ring, 0, tx_ringsize);