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

[Eric Biggers]

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.

- Eric