netdev - Re: net: Zeroing the structure ethtool_wolinfo in ethtool_get

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Date:   Tue, 23 Aug 2016 08:36:59 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Luis Henriques <luis.henriques@...onical.com>,
        Avijit Kanti Das <avijitnsec@...eaurora.org>,
        "David S . Miller" <davem@...emloft.net>,
        Ben Hutchings <ben@...adent.org.uk>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: net: Zeroing the structure ethtool_wolinfo in ethtool_get_wol()

On Tue, 2016-08-23 at 08:05 -0700, Joe Perches wrote:

> A compiler does not have a standards based requirement to
> initialize arbitrary padding bytes.
> 
> I believe gcc always does zero all padding anyway.

I would not worry for kernel code, because the amount of scrutiny there
will be enough to 'fix potential bugs' [1], but a lot of user land code
would suffer from various bugs as well that might sit there forever.

[1] Also, most call sites in the kernel are using same call stack, so
the offset of '1-7 leaked bytes' vs kernel stack is constant, making
exploits quite challenging.

Even if the current standards are lazy (are they, I did not check ?),
security needs would call for a sane compiler behavior and changing the
standards accordingly.