linux-kernel - Re: [PATCH v2 1/7] netfilter: ipset: refactor deprecated strncpy

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Message-ID: <202308101206.35C628E5@keescook>
Date:   Thu, 10 Aug 2023 12:07:39 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jan Engelhardt <jengelh@...i.de>
Cc:     Justin Stitt <justinstitt@...gle.com>,
        Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-hardening@...r.kernel.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/7] netfilter: ipset: refactor deprecated strncpy

On Wed, Aug 09, 2023 at 11:54:48PM +0200, Jan Engelhardt wrote:
> 
> On Wednesday 2023-08-09 23:40, Justin Stitt wrote:
> >On Wed, Aug 9, 2023 at 1:19 PM Florian Westphal <fw@...len.de> wrote:
> >>
> >> Justin Stitt <justinstitt@...gle.com> wrote:
> >> > Use `strscpy_pad` instead of `strncpy`.
> >>
> >> I don't think that any of these need zero-padding.
> >It's a more consistent change with the rest of the series and I don't
> >believe it has much different behavior to `strncpy` (other than
> >NUL-termination) as that will continue to pad to `n` as well.
> >
> >Do you think the `_pad` for 1/7, 6/7 and 7/7 should be changed back to
> >`strscpy` in a v3? I really am shooting in the dark as it is quite
> >hard to tell whether or not a buffer is expected to be NUL-padded or
> >not.
> 
> I don't recall either NF userspace or kernelspace code doing memcmp
> with name-like fields, so padding should not be strictly needed.

My only concern with padding is just to make sure any buffers copied to
userspace have been zeroed. I would need to take a close look at how
buffers are passed around here to know for sure...

-- 
Kees Cook