qede: confirm skb is allocated before using

qede_build_skb() assumes build_skb() always works and goes straight
to skb_reserve(). However, build_skb() can fail under memory pressure.
This results in a kernel panic because the skb to reserve is NULL.

Add a check in case build_skb() failed to allocate and return NULL.

The NULL return is handled correctly in callers to qede_build_skb().

Fixes: 8a863397 ("qede: Add build_skb() support.")
Signed-off-by: Jamie Bainbridge <jamie.bainbridge@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qlogic/qede/qede_fp.c

@@ -748,6 +748,9 @@ qede_build_skb(struct qede_rx_queue *rxq,
 	buf = page_address(bd->data) + bd->page_offset;
 	skb = build_skb(buf, rxq->rx_buf_seg_size);
 
+	if (unlikely(!skb))
+		return NULL;
+
 	skb_reserve(skb, pad);
 	skb_put(skb, len);