wan/x25_asy: integer overflow in x25_asy_change_mtu()

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 <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/net/wan/x25_asy.c b/drivers/net/wan/x25_asy.c
index 5895f1978691..fa9fdfa128c1 100644
--- 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);