Re: [PATCH 1/2] sysctl: add overflow detection to proc_get_long()

From: Al Viro <viro@ZenIV.linux.org.uk>
To: Christian Brauner <christian@brauner.io>
Cc: keescook@chromium.org, linux-kernel@vger.kernel.org,
	ebiederm@xmission.com, mcgrof@kernel.org,
	akpm@linux-foundation.org, joe.lawrence@redhat.com,
	longman@redhat.com
Subject: Re: [PATCH 1/2] sysctl: add overflow detection to proc_get_long()
Date: Sun, 14 Oct 2018 18:18:55 +0100	[thread overview]
Message-ID: <20181014171855.GW32577@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20181014132510.25943-2-christian@brauner.io>

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been replaced by simply returning ~0UL on such?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...