wan/x25_asy: integer overflow in x25_asy_change_mtu()

Dan Carpenter · davem330 · commit a28d0e873d28 · 2014-07-17T16:47:50.000-07:00
If "newmtu * 2 + 4" is too large then it can cause an integer overflow
leading to memory corruption.  Eric Dumazet suggests that 65534 is a
reasonable upper limit.

Btw, "newmtu" is not allowed to be a negative number because of the
check in dev_set_mtu(), so that's ok.

Signed-off-by: Dan Carpenter &lt;dan.carpenter@oracle.com&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;
diff --git a/drivers/net/wan/x25_asy.c b/drivers/net/wan/x25_asy.c
@@ -122,8 +122,12 @@ static int x25_asy_change_mtu(struct net_device *dev, int newmtu)
 {
 	struct x25_asy *sl = netdev_priv(dev);
 	unsigned char *xbuff, *rbuff;
-	int len = 2 * newmtu;
+	int len;
 
+	if (newmtu > 65534)
+		return -EINVAL;
+
+	len = 2 * newmtu;
 	xbuff = kmalloc(len + 4, GFP_ATOMIC);
 	rbuff = kmalloc(len + 4, GFP_ATOMIC);
 
