net/x25: fix incorrect parameter validation in the x25_getsockopt() function

The 'len' variable can't be negative when assigned the result of
'min_t' because all 'min_t' parameters are cast to unsigned int,
and then the minimum one is chosen.

To fix the logic, check 'len' as read from 'optlen',
where the types of relevant variables are (signed) int.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Gavrilov Ilia <Ilia.Gavrilov@infotecs.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/x25/af_x25.c

@@ -460,12 +460,12 @@ static int x25_getsockopt(struct socket *sock, int level, int optname,
 	if (get_user(len, optlen))
 		goto out;
 
-	len = min_t(unsigned int, len, sizeof(int));
-
 	rc = -EINVAL;
 	if (len < 0)
 		goto out;
 
+	len = min_t(unsigned int, len, sizeof(int));
+
 	rc = -EFAULT;
 	if (put_user(len, optlen))
 		goto out;