[PATCH v2] ovl: Replace offsetof() with struct_size() in ovl_stack_free()

[Thorsten Blum <thorsten.blum@linux.dev>]

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>
---
Changes in v2:
- Add missing include
- Link to v1: https://lore.kernel.org/lkml/20250503103415.281123-2-thorsten.blum@linux.dev/
---
 fs/overlayfs/util.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 0819c739cc2f..e33d2257c642 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -15,6 +15,7 @@
 #include <linux/uuid.h>
 #include <linux/namei.h>
 #include <linux/ratelimit.h>
+#include <linux/overflow.h>
 #include "overlayfs.h"
 
 /* Get write access to upper mnt - may fail if upper sb was remounted ro */
@@ -145,9 +146,9 @@ void ovl_stack_free(struct ovl_path *stack, unsigned int n)
 
 struct ovl_entry *ovl_alloc_entry(unsigned int numlower)
 {
-	size_t size = offsetof(struct ovl_entry, __lowerstack[numlower]);
-	struct ovl_entry *oe = kzalloc(size, GFP_KERNEL);
+	struct ovl_entry *oe;
 
+	oe = kzalloc(struct_size(oe, __lowerstack, numlower), GFP_KERNEL);
 	if (oe)
 		oe->__numlower = numlower;
 
-- 
2.49.0