Re: [PATCH] Change judgment len position

From: Willy Tarreau
Date: Wed Oct 24 2018 - 11:58:11 EST

On Wed, Oct 24, 2018 at 11:47:29PM +0800, Wang Hai wrote:
> To determine whether len is less than zero, it should be put before
> the function min_t, because the return value of min_t is not likely
> to be less than zero.

Huh? First, the <0 test is made on "len", not "min_t", so it still
is signed. Second, you're in fact completely removing the test here,
look :

> struct net *net = sock_net(sk);
> int val, len;
> + len = min_t(unsigned int, len, sizeof(int));
> +

len is used uninitialized here, so the result is undefined.

> if (get_user(len, optlen))
> return -EFAULT;

Then it gets overridden by get_user()

> - len = min_t(unsigned int, len, sizeof(int));
> -

Then its positive values are not bounded anymore since you moved the test.

> if (len < 0)
> return -EINVAL;

Then only negative values are dropped. So unless I'm missing something
obvious, you're just allowing len to be as large as 2GB-1 based on the
user's fed optlen.

Am I wrong ?