Re: [RESEND PATCH v2] params: Annotate struct module_param_attrs with __counted_by()

[Kees Cook <kees@kernel.org>]

On Mon, Sep 16, 2024 at 02:45:47AM -0700, Bill Wendling wrote:
> The 4294967295 simply means "I don't know." There's probably a bug in
> the size calculation. I'll look into it.

I was able to build a minimized PoC, if that's helpful:

https://godbolt.org/z/qohGd5xh1


#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

struct variable {
        int a;
        int b;
        int length;
        short array[] __attribute__((counted_by(length)));
};

struct bucket {
        int a;
        struct variable *growable;
        int b;
};

int main(int argc, char *argv[])
{
        struct bucket *p;
        struct variable *v;

        p = malloc(sizeof(*p));
        v = malloc(sizeof(*p->growable) + sizeof(*p->growable->array) * 32);
        v->length = 32;


        printf("%zu\n", __builtin_dynamic_object_size(v->array, 1));

        p->growable = v;
        printf("%zu\n", __builtin_dynamic_object_size(p->growable->array, 1));

        return 0;
}


GCC shows 64 64, but Clang shows 64 0.

-- 
Kees Cook