linux-kernel - Re: [PATCH] mmc: mmc_spi: fix snprintf() output buffer size

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Message-ID: <ab1180ff-b435-46c8-82a8-66fea41db110@wanadoo.fr>
Date: Mon, 7 Oct 2024 20:09:14 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Bartosz Golaszewski <brgl@...ev.pl>, Ulf Hansson <ulf.hansson@...aro.org>
Cc: linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] mmc: mmc_spi: fix snprintf() output buffer size

Le 07/10/2024 à 13:45, Bartosz Golaszewski a écrit :
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> GCC 13 complains about the truncated output of snprintf():
> 
> drivers/mmc/host/mmc_spi.c: In function ‘mmc_spi_response_get’:
> drivers/mmc/host/mmc_spi.c:227:64: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
>    227 |         snprintf(tag, sizeof(tag), "  ... CMD%d response SPI_%s",
>        |                                                                ^
> drivers/mmc/host/mmc_spi.c:227:9: note: ‘snprintf’ output between 26 and 43 bytes into a destination of size 32
>    227 |         snprintf(tag, sizeof(tag), "  ... CMD%d response SPI_%s",
>        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    228 |                 cmd->opcode, maptype(cmd));
> 
> Increase the size of the target buffer.
> 
> Fixes: 15a0580ced08 ("mmc_spi host driver")
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> ---
>   drivers/mmc/host/mmc_spi.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
> index 8fee7052f2ef..fa1d1a1b3142 100644
> --- a/drivers/mmc/host/mmc_spi.c
> +++ b/drivers/mmc/host/mmc_spi.c
> @@ -222,7 +222,7 @@ static int mmc_spi_response_get(struct mmc_spi_host *host,
>   	u8 	leftover = 0;
>   	unsigned short rotator;
>   	int 	i;
> -	char	tag[32];
> +	char	tag[43];
>   
>   	snprintf(tag, sizeof(tag), "  ... CMD%d response SPI_%s",
>   		cmd->opcode, maptype(cmd));

'tag' is only used in a dev_dbg() at the end of the function.

Maybe "  ... CMD%d response SPI_%s" could me moved directly within the 
dev_dbg(). This would save a few bytes on the stack, save a snprintf() 
in the normal path and fix the warning without the need of magic number.

just my 2c.

CJ