linux-hardening - Re: [PATCH 54/64] ipv6: Use struct_group() to zero rt6

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Date:   Thu, 29 Jul 2021 11:58:50 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-hardening@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH 54/64] ipv6: Use struct_group() to zero rt6_info

On Tue, 27 Jul 2021 13:58:45 -0700 Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memset(), avoid intentionally writing across
> neighboring fields.
> 
> Add struct_group() to mark region of struct rt6_info that should be
> initialized to zero.

memset_after() ?

> diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
> index 15b7fbe6b15c..9816e7444918 100644
> --- a/include/net/ip6_fib.h
> +++ b/include/net/ip6_fib.h
> @@ -205,20 +205,22 @@ struct fib6_info {
>  
>  struct rt6_info {
>  	struct dst_entry		dst;
> -	struct fib6_info __rcu		*from;
> -	int				sernum;
> -
> -	struct rt6key			rt6i_dst;
> -	struct rt6key			rt6i_src;
> -	struct in6_addr			rt6i_gateway;
> -	struct inet6_dev		*rt6i_idev;
> -	u32				rt6i_flags;
> -
> -	struct list_head		rt6i_uncached;
> -	struct uncached_list		*rt6i_uncached_list;
> -
> -	/* more non-fragment space at head required */
> -	unsigned short			rt6i_nfheader_len;
> +	struct_group(init,
> +		struct fib6_info __rcu		*from;
> +		int				sernum;
> +
> +		struct rt6key			rt6i_dst;
> +		struct rt6key			rt6i_src;
> +		struct in6_addr			rt6i_gateway;
> +		struct inet6_dev		*rt6i_idev;
> +		u32				rt6i_flags;
> +
> +		struct list_head		rt6i_uncached;
> +		struct uncached_list		*rt6i_uncached_list;
> +
> +		/* more non-fragment space at head required */
> +		unsigned short			rt6i_nfheader_len;
> +	);
>  };
>  
>  struct fib6_result {
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 6b8051106aba..bbcc605bab57 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -327,9 +327,7 @@ static const struct rt6_info ip6_blk_hole_entry_template = {
>  
>  static void rt6_info_init(struct rt6_info *rt)
>  {
> -	struct dst_entry *dst = &rt->dst;
> -
> -	memset(dst + 1, 0, sizeof(*rt) - sizeof(*dst));
> +	memset(&rt->init, 0, sizeof(rt->init));
>  	INIT_LIST_HEAD(&rt->rt6i_uncached);
>  }
>