Re: [PATCH v2] soc: qcom: cmd-db: replace strscpy_pad() with strncpy()

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 28/06/2022 02:18, Douglas Anderson wrote:
> 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.
> 
> While we're at it, let's change the query array to use
> "sizeof(ent->id)" so it can't possibly go out of sync with our later
> copy.
> 
> Fixes: ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with strscpy_pad()")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
> 
> ---
> 
> Changes in v2:
> - Size array with "sizeof(ent->id)"
> 
>  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..ffd2660b2890 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[sizeof(ent->id)] __nonstring;
>  
>  	ret = cmd_db_ready();
>  	if (ret)
>  		return ret;
>  
>  	/* Pad out query string to same length as in DB */

I would find useful a comment that length of the ID can be equal to
sizeof(query)... so no one will need to increment the counter of wasted
time on this. :)

But beside that, thanks for the fix:

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

> -	strscpy_pad(query, id, sizeof(query));
> +	strncpy(query, id, sizeof(query));
>  
>  	for (i = 0; i < MAX_SLV_ID; i++) {
>  		rsc_hdr = &cmd_db_header->header[i];


Best regards,
Krzysztof