Make use of the struct_size() helper to calculate the size of struct
fsverity_digest instead of an open-coded version, in order to get rid
of the warning by sparse.

Also, address the following sparse warning:
fs/verity/enable.c:205:28: warning: using sizeof on a flexible structure

Signed-off-by: Zhang Jianhua <chris.zjh@huawei.com>
---
v2:
- change the commit message from bugfix to cleanup

 fs/verity/enable.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/verity/enable.c b/fs/verity/enable.c
index f75d2c010f36..075dc0aa5416 100644
--- a/fs/verity/enable.c
+++ b/fs/verity/enable.c
@@ -201,7 +201,7 @@ static int enable_verity(struct file *filp,
 	const struct fsverity_operations *vops = inode->i_sb->s_vop;
 	struct merkle_tree_params params = { };
 	struct fsverity_descriptor *desc;
-	size_t desc_size = sizeof(*desc) + arg->sig_size;
+	size_t desc_size = struct_size(desc, signature, arg->sig_size);
 	struct fsverity_info *vi;
 	int err;
 
-- 
2.31.0

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

- Eric

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.

- Eric

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.

Johan

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