linux-kernel - Re: [PATCH] soc: qcom: cmd-db: replace strscpy

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Message-Id: <20220627235248.43895C34115@smtp.kernel.org>
Date:   Mon, 27 Jun 2022 16:52:46 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Douglas Anderson <dianders@...omium.org>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] soc: qcom: cmd-db: replace strscpy_pad() with strncpy()

Quoting Douglas Anderson (2022-06-27 16:17:00)
> Commit ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with
> strscpy_pad()") breaks booting on my sc7280-herobrine-herobrine
> device. From printouts I see that at bootup the function is called
> with an id of "lnbclka2" which is 8 bytes big.
> 
> Previously all 8 bytes of this string were copied to the
> destination. Now only 7 bytes will be copied since strscpy_pad() saves
> a byte for '\0' termination.
> 
> We don't need the '\0' termination in the destination. Let's go back
> to strncpy(). According to the warning:
>   If a caller is using non-NUL-terminated strings, strncpy() can still
>   be used, but destinations should be marked with the __nonstring
>   attribute to avoid future compiler warnings.
> ...so we'll do that.
> 
> Fixes: ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with strscpy_pad()")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
>  drivers/soc/qcom/cmd-db.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
> index c5137c25d819..0aafe90277bc 100644
> --- a/drivers/soc/qcom/cmd-db.c
> +++ b/drivers/soc/qcom/cmd-db.c
> @@ -141,14 +141,14 @@ static int cmd_db_get_header(const char *id, const struct entry_header **eh,
>         const struct rsc_hdr *rsc_hdr;
>         const struct entry_header *ent;
>         int ret, i, j;
> -       u8 query[8];
> +       u8 query[8] __nonstring;

Since you're already here, can you change 8 to be sizeof(ent->id)? That
would directly tie the two lengths together so that one can't change and
then the carefully crafted strncpy() fails again.

>  
>         ret = cmd_db_ready();
>         if (ret)
>                 return ret;
>  
>         /* Pad out query string to same length as in DB */
> -       strscpy_pad(query, id, sizeof(query));
> +       strncpy(query, id, sizeof(query));