linux-hardening - Re: [PATCH] firmware: tegra: bpmp: refactor deprecated strncpy

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Date:   Thu, 14 Sep 2023 21:00:57 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] firmware: tegra: bpmp: refactor deprecated strncpy

On Wed, Sep 13, 2023 at 07:38:44PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> It seems like the filename stored at `namevirt` is expected to be
> NUL-terminated.

This took me a bit to establish, but yes: buf[256] is used to store
filename, so it'll always be %NUL-terminated with the 256 bytes, which
is the same size used to allocate virtname, which means it will always
be %NUL-terminated.

> 
> A suitable replacement is `strscpy_pad` due to the fact that it
> guarantees NUL-termination on the destination buffer whilst maintaining
> the NUL-padding behavior that strncpy provides.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

This one looks weird because namevirt seems unused, but I assume there's
some kind of DMA side-effect happening somewhere?

But, yes, after digging around here, I think this all looks right.

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

-- 
Kees Cook