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SubjectRe: [PATCH] Change judgment len position
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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

> 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 ?
>
> Willychee

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