exec: Fix incorrect type for ret

In the setup_arg_pages(), ret is declared as an unsigned long.
The ret might take a negative value. Therefore, its type should
be changed to int.

Signed-off-by: Xichao Zhao <zhao.xichao@vivo.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20250825073609.219855-1-zhao.xichao@vivo.com
Signed-off-by: Kees Cook <kees@kernel.org>

Author: Xichao Zhao

fs/exec.c

@@ -599,7 +599,7 @@ int setup_arg_pages(struct linux_binprm *bprm,
 		    unsigned long stack_top,
 		    int executable_stack)
 {
-	unsigned long ret;
+	int ret;
 	unsigned long stack_shift;
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma = bprm->vma;