linux-kernel - Re: [PATCH 1/2] sysctl: add overflow detection to proc_get

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Date:   Sun, 14 Oct 2018 18:18:55 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Christian Brauner <christian@...uner.io>
Cc:     keescook@...omium.org, linux-kernel@...r.kernel.org,
        ebiederm@...ssion.com, mcgrof@...nel.org,
        akpm@...ux-foundation.org, joe.lawrence@...hat.com,
        longman@...hat.com
Subject: Re: [PATCH 1/2] sysctl: add overflow detection to proc_get_long()

On Sun, Oct 14, 2018 at 03:25:09PM +0200, Christian Brauner wrote:

> +static unsigned long sysctl_strtoul_lenient(const char *cp, char **endp,
> +					    unsigned int base, bool *overflow)
> +{
> +	unsigned long long result;
> +	unsigned int rv;
> +
> +	cp = _parse_integer_fixup_radix(cp, &base);
> +	rv = _parse_integer(cp, base, &result);
> +	if ((rv & KSTRTOX_OVERFLOW) ||
> +	    (result != (unsigned long long)(unsigned long)result))
> +		*overflow = true;
> +	else
> +		*overflow = false;

Yecchh...  First of all, the cast back to unsigned long long is completely
pointless.  What's more,
	if (expr)
		foo = true;
	else
		foo = flase;
is a fairly unidiomatic way to spell foo = expr;

And... is there anything that would really care if this "overflow" thing had
been replaced by simply returning ~0UL on such?  That would appear to be
a lot more natural API...