# Re: [PATCH] Change judgment len position

From: Willy Tarreau
Date: Wed Oct 24 2018 - 12:33:11 EST

On Wed, Oct 24, 2018 at 09:23:19AM -0700, Joe Perches wrote:
> On Wed, 2018-10-24 at 17:57 +0200, Willy Tarreau wrote:
> > 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.
>
> Not quite.
>
> Problem here is negative values are tested as
> large positive values and limited to 4
>
> ie:
> ien len = -1,
> len = min_t(unsigned int, len, sizeof(int));
>
> len is now 4
>
> > > if (len < 0)
> > > return -EINVAL;
>
> So this test len < 0 could be moved up above min_t

It could indeed, or we could also have min_t() done on an int instead
of an unsigned int and this would avoid the need to shuffle the code
around and open a huge hole like this one.

Willy