irda: Fix heap memory corruption in iriap.c

While parsing the GetValuebyClass command frame, we could potentially write
passed the skb->data pointer.

Cc: stable@kernel.org
Reported-by: NIlja Van Sprundel <ivansprundel@ioactive.com>
Signed-off-by: NSamuel Ortiz <samuel@sortiz.org>

net/irda/iriap.c

@@ -502,7 +502,8 @@ static void iriap_getvaluebyclass_confirm(struct iriap_cb *self,
 		IRDA_DEBUG(4, "%s(), strlen=%d\n", __func__, value_len);
 
 		/* Make sure the string is null-terminated */
-		fp[n+value_len] = 0x00;
+		if (n + value_len < skb->len)
+			fp[n + value_len] = 0x00;
 		IRDA_DEBUG(4, "Got string %s\n", fp+n);
 
 		/* Will truncate to IAS_MAX_STRING bytes */