Subject: Re: [RFC PATCH v3 17/19] samples/landlock: Replace atoi() with strtoull() in populate_ruleset_net()

From: "Günther Noack" <[email-masked]>
Date: Fri, 27 Sep 2024 17:12:50 +0200

On Wed, Sep 04, 2024 at 06:48:22PM +0800, Mikhail Ivanov wrote:
> Add str2num() helper and replace atoi() with it. atoi() does not provide
> overflow checks, checks of invalid characters in a string and it is
> recommended to use strtol-like functions (Cf. atoi() manpage).
> 
> Signed-off-by: Mikhail Ivanov <[email-masked]>
> ---
>  samples/landlock/sandboxer.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> index e8223c3e781a..d4dba9e4ce89 100644
> --- a/samples/landlock/sandboxer.c
> +++ b/samples/landlock/sandboxer.c
> @@ -150,6 +150,26 @@ static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
>  	return ret;
>  }
>  
> +static int str2num(const char *numstr, unsigned long long *num_dst)
> +{
> +	char *endptr = NULL;
> +	int err = 1;
> +	unsigned long long num;
> +
> +	errno = 0;
> +	num = strtoull(numstr, &endptr, 0);
> +	if (errno != 0)
> +		goto out;
> +
> +	if (*endptr != '\0')
> +		goto out;
> +
> +	*num_dst = num;
> +	err = 0;
> +out:
> +	return err;
> +}

I believe if numstr is the empty string, str2num would return success and set
num_dst to 0, which looks unintentional to me.

Do we not have a better helper for this that we can link from here?

> +
>  static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
>  				const __u64 allowed_access)
>  {
> @@ -168,7 +188,12 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
>  
>  	env_port_name_next = env_port_name;
>  	while ((strport = strsep(&env_port_name_next, ENV_DELIMITER))) {
> -		net_port.port = atoi(strport);
> +		if (str2num(strport, &net_port.port)) {
> +			fprintf(stderr,
> +				"Failed to convert \"%s\" into a number\n",
> +				strport);
> +			goto out_free_name;
> +		}
>  		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT,
>  				      &net_port, 0)) {
>  			fprintf(stderr,
> -- 
> 2.34.1
>