p54spi: compensate firmware alignment bug in p54spi_rx

Firmware may insert up to 4 padding bytes after the lmac header,
but it does not amend the size of SPI data transfer.
Such packets has correct data size in header, thus referencing
past the end of allocated skb. Put extra 4 bytes to the end of the
received skb to compensate for this case.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Acked-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/p54/p54spi.c

@@ -395,14 +395,22 @@ static int p54spi_rx(struct p54s_priv *priv)
 		return 0;
 	}
 
-	skb = dev_alloc_skb(len);
+
+	/* Firmware may insert up to 4 padding bytes after the lmac header,
+	 * but it does not amend the size of SPI data transfer.
+	 * Such packets has correct data size in header, thus referencing
+	 * past the end of allocated skb. Reserve extra 4 bytes for this case */
+	skb = dev_alloc_skb(len + 4);
 	if (!skb) {
 		dev_err(&priv->spi->dev, "could not alloc skb");
 		return 0;
 	}
 
 	p54spi_spi_read(priv, SPI_ADRS_DMA_DATA, skb_put(skb, len), len);
 	p54spi_sleep(priv);
+	/* Put additional bytes to compensate for the possible
+	 * alignment-caused truncation */
+	skb_put(skb, 4);
 
 	if (p54_rx(priv->hw, skb) == 0)
 		dev_kfree_skb(skb);