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

[Zhang Jianhua]

Make use of the struct_size() to calculate the size of struct
fsverity_digest instead of an open-coded version, in order to
get rid of the sparse warnings about flexible structure.

As reported by sparse:
fs/verity/measure.c:48:9: warning: using sizeof on a flexible structure
fs/verity/measure.c:52:38: warning: using sizeof on a flexible structure

Signed-off-by: Zhang Jianhua <chris.zjh@xxxxxxxxxx>
---
v2:
- change the commit message from bugfix to cleanup
 fs/verity/measure.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/verity/measure.c b/fs/verity/measure.c
index e99c00350c28..4a388116d0de 100644
--- a/fs/verity/measure.c
+++ b/fs/verity/measure.c
@@ -27,6 +27,7 @@ int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
 	const struct fsverity_info *vi;
 	const struct fsverity_hash_alg *hash_alg;
 	struct fsverity_digest arg;
+	size_t arg_size = struct_size(&arg, digest, 0);
 
 	vi = fsverity_get_info(inode);
 	if (!vi)
@@ -44,11 +45,11 @@ int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
 	if (arg.digest_size < hash_alg->digest_size)
 		return -EOVERFLOW;
 
-	memset(&arg, 0, sizeof(arg));
+	memset(&arg, 0, arg_size);
 	arg.digest_algorithm = hash_alg - fsverity_hash_algs;
 	arg.digest_size = hash_alg->digest_size;
 
-	if (copy_to_user(uarg, &arg, sizeof(arg)))
+	if (copy_to_user(uarg, &arg, arg_size))
 		return -EFAULT;
 
 	if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size))
-- 
2.31.0