Re: [PATCH] fsverity: Fix bpf_get_fsverity_digest() dynptr assumptions

[Kumar Kartikeya Dwivedi]

On Sat, 1 Aug 2026 at 22:18, Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
>
> On Sat, Aug 01, 2026 at 07:38:08PM +0200, Kumar Kartikeya Dwivedi wrote:
> > On Sat Aug 1, 2026 at 7:35 PM CEST, Kumar Kartikeya Dwivedi wrote:
> > > On Sat Aug 1, 2026 at 7:15 PM CEST, Eric Biggers wrote:
> > >> On Sat, Aug 01, 2026 at 06:52:45PM +0200, Kumar Kartikeya Dwivedi wrote:
> > >>> > Also correctly handle sizes over INT_MAX, which previously caused an
> > >>> > integer overflow and crash.  __bpf_dynptr_size() returns a u64.
> > >>> >
> > >>>
> > >>> I guess this occurs when using file dynptrs? Otherwise the size is capped to
> > >>> DYNPTR_SIZE_MASK.
> > >>
> > >> Yes, though it looks like __bpf_dynptr_data_rw() excludes file dynptrs.
> > >> So this particular issue might be unreachable.  Still seems like a good
> > >> idea to match the u64 type that __bpf_dynptr_size() returns though.
> > >>
> > >
> > > I don't see this in patchwork, so you might have to resend this with [PATCH
> > > bpf-next] subject again to trigger CI if you want this to go through bpf tree.
> > >
> >
> > Sorry, [PATCH bpf], rather.
>
> Sure I can do that.
>
> Would it be okay to also make this function return -EOVERFLOW if
> out_digest_sz is too small, similar to FS_IOC_MEASURE_VERITY, instead of
> silently truncating?  The silent truncation is a footgun.

Yeah, I think it makes sense. I will also ping Song to ack this on
Monday (or your new version).
Thanks

>
> - Eric