linux-hardening - Re: [PATCH RFC 1/3] powerpc/ps3: refactor strncpy usage attempt 1

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Date:   Mon, 14 Aug 2023 22:28:36 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Justin Stitt <justinstitt@...gle.com>,
        Geoff Levand <geoff@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Justin Stitt <justinstitt@...gle.com>
Subject: Re: [PATCH RFC 1/3] powerpc/ps3: refactor strncpy usage attempt 1

Justin Stitt <justinstitt@...gle.com> writes:
> This approach simply replicates the implementation of `make_field` which
> means we drop `strncpy` for `memcpy`.
>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
>  arch/powerpc/platforms/ps3/repository.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/platforms/ps3/repository.c b/arch/powerpc/platforms/ps3/repository.c
> index 205763061a2d..1abe33fbe529 100644
> --- a/arch/powerpc/platforms/ps3/repository.c
> +++ b/arch/powerpc/platforms/ps3/repository.c
> @@ -73,9 +73,9 @@ static void _dump_node(unsigned int lpar_id, u64 n1, u64 n2, u64 n3, u64 n4,
>  
>  static u64 make_first_field(const char *text, u64 index)
>  {
> -	u64 n;
> +	u64 n = 0;
>  
> -	strncpy((char *)&n, text, 8);
> +	memcpy((char *)&n, text, strnlen(text, sizeof(n)));
>  	return PS3_VENDOR_ID_NONE + (n >> 32) + index;
>  }

I guess it's a slight improvement, because people generally know
memcpy's behaviour better than strncpy.

The change log should be a bit more verbose and mention that the result
is the same, including the NULL padding done my strncpy().

cheers