linux-hardening - Re: [RESEND PATCH] mux: Convert mux_control_ops to a flex array member in mux

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Message-ID: <65DBE926-C9B0-4394-ACD8-D3C71AABD064@oracle.com>
Date: Wed, 5 Mar 2025 17:31:13 +0000
From: Qing Zhao <qing.zhao@...cle.com>
To: Kees Cook <kees@...nel.org>
CC: Thorsten Blum <thorsten.blum@...ux.dev>, Bill Wendling <morbo@...gle.com>,
        Peter Rosin <peda@...ntia.se>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: Re: [RESEND PATCH] mux: Convert mux_control_ops to a flex array
 member in mux_chip



> On Mar 4, 2025, at 23:57, Kees Cook <kees@...nel.org> wrote:
> 
> #include <stdlib.h>
> #include <stdio.h>
> 
> struct foo {
>    int count;
>    int array[] __attribute__((__counted_by__(count)));
> };
> 
> int main(int argc, char *argv[]) {
>    int num_elems = 2 + argc;
> 
>    struct foo *p = malloc(sizeof(*p) + num_elems * sizeof(*p->array) + sizeof(int));
>    p->count = num_elems;
> 
>    // this correctly trips sanitizer:
>    int val = p->array[num_elems];
>    printf("%d\n", val);
> 
>    // this does not?!
>    int *valp = &p->array[num_elems];
>    printf("%p %d\n", valp, *valp);
> 
>    return 0;
> }