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SubjectRe: [PATCH v3] fs: fix unintentional arithmetic wraparound in offset calculation
On Fri, May 17, 2024 at 02:26:47AM +0100, Al Viro wrote:
> On Fri, May 17, 2024 at 02:13:22AM +0100, Matthew Wilcox wrote:
> > On Fri, May 17, 2024 at 12:29:06AM +0000, Justin Stitt wrote:
> > > When running syzkaller with the newly reintroduced signed integer
> > > overflow sanitizer we encounter this report:
> >
> > why do you keep saying it's unintentional? it's clearly intended.
>
> Because they are short on actual bugs to be found by their tooling
> and attempt to inflate the sound/noise rate; therefore, every time

"short on bugs"? We're trying to drive it to zero. I would *love* to be
short on bugs. See my reply[1] to Ted.

> when overflow _IS_ handled correctly, it must have been an accident -
> we couldn't have possibly done the analysis correctly. And if somebody
> insists that they _are_ capable of basic math, they must be dishonest.
> So... "unintentional" it's going to be.

As Justin said, this is a poor choice in wording. In other cases I've
tried to describe this as making changes so that intent is unambiguous
(to both a human and a compiler).

> <southpark> Math is hard, mmkay? </southpark>
>
> Al, more than slightly annoyed by that aspect of the entire thing...

I'm sorry about that. None of this is a commentary on code correctness;
we're just trying to refactor things so that the compiler can help us
catch the _unintended_ overflows. This one is _intended_, so here we are
to find a palatable way to leave the behavior unchanged while gaining
compiler coverage.

-Kees

[1] https://lore.kernel.org/linux-hardening/202405171329.019F2F566C@keescook/

--
Kees Cook

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