Re: [PATCH] bpf: Fix KASAN use-after-free Read in compute_effective_progs

[Tadeusz Struk]

On 4/13/22 12:07, Andrii Nakryiko wrote:
> > it would be ideal if detach would never fail, but it would require some kind of
> > prealloc, on attach maybe? Another option would be to minimize the probability
> We allocate new arrays in update_effective_progs() under assumption
> that we might need to grow the array because we use
> update_effective_progs() for attachment. But for detachment we know
> that we definitely don't need to increase the size, we need to remove
> existing element only, thus shrinking the size.
>
> Normally we'd reallocate the array to shrink it (and that's why we use
> update_effective_progs() and allocate memory), but we can also have a
> fallback path for detachment only to reuse existing effective arrays
> and just shift all the elements to the right from the element that's
> being removed. We'll leave NULL at the end, but that's much better
> than error out. Subsequent attachment or detachment will attempt to
> properly size and reallocate everything.
>
> So I think that should be the fix, if you'd be willing to work on it.

That makes it much easier then. I will change it so that there is no
alloc needed on the detach path. Thanks for the clarification.

--
Thanks,
Tadeusz