Re: [PATCH -next v2] fs-verity: Use struct_size() helper in enable_verity()

Eric Biggers
2022-05-19T16:57:23Z

On Thu, May 19, 2022 at 01:24:45PM +0200, Johan Hovold wrote:
> On Wed, May 18, 2022 at 08:17:59PM -0700, Eric Biggers wrote:
> > On Wed, May 18, 2022 at 08:06:04PM -0700, Eric Biggers wrote:
> > > On Thu, May 19, 2022 at 10:24:50AM +0800, Zhang Jianhua wrote:
> > > > Also, address the following sparse warning:
> > > > fs/verity/enable.c:205:28: warning: using sizeof on a flexible structure
> > >
> > > How can I reproduce this warning? I am using the latest version of sparse, and
> > > I don't see any of these warnings you're reporting.
> > >
> > > $ sparse --version
> > > v0.6.4
> > > $ make C=2 fs/verity/
> > > CHECK scripts/mod/empty.c
> > > CALL scripts/checksyscalls.sh
> > > CALL scripts/atomic/check-atomics.sh
> > > DESCEND objtool
> > > CHECK fs/verity/enable.c
> > > CHECK fs/verity/hash_algs.c
> > > CHECK fs/verity/init.c
> > > CHECK fs/verity/measure.c
> > > CHECK fs/verity/open.c
> > > CHECK fs/verity/read_metadata.c
> > > CHECK fs/verity/verify.c
> > > CHECK fs/verity/signature.c
> > >
> >
> > 'make C=2 CHECK="sparse -Wflexible-array-sizeof"' does the trick. However, it
> > produces a *lot* of warnings all over the place.
> >
> > Unless there is an effort to actually address all of these so that this warning
> > can be enabled by default, I don't see the poinnt in addressing these just for
> > the warnings sake. The change to fsverity_ioctl_measure() is definitely just
> > for the warning's sake, so I don't really want to do that one. The change to
> > enable_verity() is a bit less useless, so I could still take that one.
>
> Importantly, struct_size() still relies on sizeof() so this has zero
> effect on those sparse warnings.
>

Yeah, you're right. In fact struct_size() generates two warnings, whereas
directly writing sizeof only generates 1! So clearly sparse's
-Wflexible-array-sizeof warning is useless as-is.

I'm still keeping this patch, but I updated the commit message to not claim that
it addresses a sparse warning. Now it's just:

fs-verity: Use struct_size() helper in enable_verity()

Follow the best practice for allocating a variable-sized structure.

- Eric