HSI: ssi_protocol: double free in ssip_pn_xmit()

BugLink: http://bugs.launchpad.net/bugs/1764762

[ Upstream commit 30260501 ]

If skb_pad() fails then it frees skb and we don't need to free it again
at the end of the function.

Fixes: dc7bf5d7 ("HSI: Introduce driver for SSI Protocol")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/hsi/clients/ssi_protocol.c

@@ -976,7 +976,7 @@ static int ssip_pn_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto drop;
 	/* Pad to 32-bits - FIXME: Revisit*/
 	if ((skb->len & 3) && skb_pad(skb, 4 - (skb->len & 3)))
-		goto drop;
+		goto inc_dropped;
 
 	/*
 	 * Modem sends Phonet messages over SSI with its own endianess...
@@ -1028,8 +1028,9 @@ static int ssip_pn_xmit(struct sk_buff *skb, struct net_device *dev)
 drop2:
 	hsi_free_msg(msg);
 drop:
-	dev->stats.tx_dropped++;
 	dev_kfree_skb(skb);
+inc_dropped:
+	dev->stats.tx_dropped++;
 
 	return 0;
 }