4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: John Fastabend <john.fastabend@gmail.com>

[ Upstream commit 3de03596dfeee48bc803c1d1a6daf60a459929f3 ]

Fix possible null pointer dereference that may occur when calling
skb_reserve() on a null skb.

Fixes: 879c7220e82 ("net: pktgen: Observe needed_headroom of the device")
Signed-off-by: John Fastabend <redacted>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/core/pktgen.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c

@@ -2787,7 +2787,9 @@ static struct sk_buff *pktgen_alloc_skb(
 	} else {
 		 skb = __netdev_alloc_skb(dev, size, GFP_NOWAIT);
 	}
-	skb_reserve(skb, LL_RESERVED_SPACE(dev));
+
+	if (likely(skb))
+		skb_reserve(skb, LL_RESERVED_SPACE(dev));
 
 	return skb;
 }