ovl: Replace offsetof() with struct_size() in ovl_cache_entry_new()

Compared to offsetof(), struct_size() provides additional compile-time
checks for structs with flexible arrays (e.g., __must_be_array()).

No functional changes intended.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: toblux

fs/overlayfs/readdir.c

@@ -13,6 +13,7 @@
 #include <linux/security.h>
 #include <linux/cred.h>
 #include <linux/ratelimit.h>
+#include <linux/overflow.h>
 #include "overlayfs.h"
 
 struct ovl_cache_entry {
@@ -147,9 +148,8 @@ static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
 						   u64 ino, unsigned int d_type)
 {
 	struct ovl_cache_entry *p;
-	size_t size = offsetof(struct ovl_cache_entry, name[len + 1]);
 
-	p = kmalloc(size, GFP_KERNEL);
+	p = kmalloc(struct_size(p, name, len + 1), GFP_KERNEL);
 	if (!p)
 		return NULL;