linux-hardening - Re: [RFC][PATCH v3 1/3] Fix unefficient call to memset before memcpu in nla

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Message-ID: <202010211646.28D4C5642@keescook>
Date:   Wed, 21 Oct 2020 16:46:23 -0700
From:   Kees Cook <keescook@...omium.org>
To:     laniel_francis@...vacyrequired.com
Cc:     linux-hardening@...r.kernel.org, netdev@...r.kernel.org,
        davem@...emloft.net, kuba@...nel.org
Subject: Re: [RFC][PATCH v3 1/3] Fix unefficient call to memset before memcpu
 in nla_strlcpy.

On Tue, Oct 20, 2020 at 06:47:05PM +0200, laniel_francis@...vacyrequired.com wrote:
> From: Francis Laniel <laniel_francis@...vacyrequired.com>
> 
> Before this commit, nla_strlcpy first memseted dst to 0 then wrote src into it.
> This is inefficient because bytes whom number is less than src length are written
> twice.
> 
> This patch solves this issue by first writing src into dst then fill dst with
> 0's.
> Note that, in the case where src length is higher than dst, only 0 is written.
> Otherwise there are as many 0's written to fill dst.
> 
> For example, if src is "foo\0" and dst is 5 bytes long, the result will be:
> 1. "fooGG" after memcpy (G means garbage).
> 2. "foo\0\0" after memset.
> 
> Signed-off-by: Francis Laniel <laniel_francis@...vacyrequired.com>

Looks good! (If there are future versions of this series, I think you
can drop the RFC part...)

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook