Subject: Re: [PATCH 01/64] media: omap3isp: Extract struct group for memcpy() region

From: Kees Cook <[email-masked]>
Date: Fri, 30 Jul 2021 09:44:00 -0700

On Fri, Jul 30, 2021 at 12:00:54PM +0300, Dan Carpenter wrote:
> On Fri, Jul 30, 2021 at 10:38:45AM +0200, David Sterba wrote:
> > Then is explicit memset the only reliable way accross all compiler
> > flavors and supported versions?
> > 
> 
> The = { } initializer works.  It's only when you start partially
> initializing the struct that it doesn't initialize holes.

No, partial works. It's when you _fully_ initialize the struct where the
padding doesn't get initialized. *sob*

struct foo {
	u8 flag;
	/* padding */
	void *ptr;
};

These are fine:

struct foo ok1 = { };
struct foo ok2 = { .flag = 7 };
struct foo ok3 = { .ptr = NULL };

This is not:

struct foo bad = { .flag = 7, .ptr = NULL };

(But, of course, it depends on padding size, compiler version, and
architecture. i.e. things remain unreliable.)

-- 
Kees Cook