PR analyzer/94362 Partial Fix

[brian.sobulefsky]

Agreed too. Generic "error on overflow" is not an answer, and ignoring overflow
is not an answer either because flagging faulty memory allocations is an
important feature.

Brian


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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, March 2, 2021 6:09 PM, Jeff Law <jeffreyalaw@gmail.com> wrote:

> On 3/2/21 6:40 PM, David Malcolm via Gcc-patches wrote:
>
> > > My devil's advocate position would be if the analyzer raises
> > > exception on
> > > any possible overflow, will that overwhelm the user with false
> > > positives?
> > > Presumably by "raise exception" you mean "issue a diagnostic and stop
> > > analyzing this path", right?
> >
> > I think the point is to detect where numerical overflow can lead to
> > e.g. a buffer overflow, rather than complain about numerical overflow
> > in its own right, like in the make_arr example I gave earlier.
>
> WRT overflow, IMHO, the most valuable case to detect overflows is when
> they feed an allocation via malloc/alloca.  If an attacker can arrange
> to overflow the size computation, then they can cause an
> under-allocation which in turn opens the ability to over-write the stack
> or heap data structures, which in turn are great attack vectors.
>
> And in case you think that's contrived, it isn't :-)
>
> http://phrack.org/issues/67/9.html
>
> > > I
> > > am not sure of the answer here, because a piece of me feels that
> > > overflow is not
> > > something that production code should be relying on in any serious
> > > application,
> > > and so should be non existent, but I am not sure if that is
> > > reflective of
> > > reality.
> > > My belief is that production code is full of overflows, but only some
> > > of them are security-sensitive. Consider e.g. hashing algorithms that
> > > sum some values and beningly assume overflow for wraparound as opposed
> > > to the "calculate the size of the buffer to be allocated" example
> > > (where the overflow is a classic security pitfall).
>
> Agreed.
>
> Jeff