[Skiboot] [PATCH] Fix FTBFS with -Werror=format-overflow

[Andrew Donnellan]

On 26/01/18 00:14, Frédéric Bonnard wrote:
> i2c.c fails to compile with gcc7 and -Werror=format-overflow used in
> Debian Unstable and Ubuntu 18.04 :
> 
> i2c.c: In function ‘i2c_init’:
> i2c.c:211:15: error: ‘%s’ directive writing up to 255 bytes into a
> region of size 236 [-Werror=format-overflow=]
> 
> We just make sure we never write more than what the destination can
> store.
> 
> Signed-off-by: Frédéric Bonnard <frediz at linux.vnet.ibm.com>
> ---
>   external/opal-prd/i2c.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/external/opal-prd/i2c.c b/external/opal-prd/i2c.c
> index ba4b3c85..dca303e4 100644
> --- a/external/opal-prd/i2c.c
> +++ b/external/opal-prd/i2c.c
> @@ -234,7 +234,13 @@ void i2c_init(void)
>   			continue;
>   
>   		/* Get bus name */
> -		sprintf(dpath, SYSFS "/class/i2c-dev/%s/name", devent->d_name);
> +		if (snprintf(dpath, NAME_MAX, SYSFS "/class/i2c-dev/%s/name",
> +					devent->d_name) < 0 ) {

If the string is too long, snprintf() will truncate and return number of 
bytes written, not a negative error code.

> +			pr_log(LOG_ERR, "I2C: bus name longer than NAME_MAX : "

Strictly speaking, the bus name doesn't have to be longer than NAME_MAX, 
it's the entire path.

I suspect that dpath should actually be of length PATH_MAX...


Andrew

> +					SYSFS "/class/i2c-dev/%s/name",
> +					devent->d_name);
> +			return;
> +		}
>   		f = fopen(dpath, "r");
>   		if (!f) {
>   			pr_log(LOG_NOTICE, "I2C: Can't open %s: %m, skipping.",
> 

-- 
Andrew Donnellan              OzLabs, ADL Canberra
andrew.donnellan at au1.ibm.com  IBM Australia Limited