linux-kernel - Re: [PATCH RFC] brcmfmac: sanitize DMI strings v2

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Date:   Mon, 06 May 2019 15:29:21 +0300
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Victor Bravo <1905@...blk.com>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Arend Van Spriel <arend.vanspriel@...adcom.com>,
        Franky Lin <franky.lin@...adcom.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Chi-Hsien Lin <chi-hsien.lin@...ress.com>,
        Wright Feng <wright.feng@...ress.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org,
        brcm80211-dev-list.pdl@...adcom.com,
        brcm80211-dev-list@...ress.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] brcmfmac: sanitize DMI strings v2

Victor Bravo <1905@...blk.com> writes:

> On Mon, May 06, 2019 at 11:42:06AM +0300, Kalle Valo wrote:
>> Hans de Goede <hdegoede@...hat.com> writes:
>> 
>> >> @@ -99,6 +107,15 @@ static const struct dmi_system_id dmi_platform_data[] = {
>> >>   	{}
>> >>   };
>> >>   +void brcmf_dmi_sanitize(char *dst, const unsigned char *allowed,
>> >> char safe)
>> >> +{
>> >> +	while (*dst) {
>> >> +		if ((*dst < 0) || !(allowed[*dst / 8] & (1 << (*dst % 8))))
>> >
>> > At a first look I have no clue what this code is doing and I honestly do not feel
>> > like figuring it out, this is clever, but IMHO not readable.
>> >
>> > Please just write this as if (*dst < 0x21 || (*dst > foo && < bar) || etc,
>> > so that a human can actually see in one look what the code is doing.
>> 
>> Is there an existing function for sanitising filenames so that we don't
>> need to reinvent the wheel, maybe something like isalnum()?
>
> I would definitely prefer to use existing function, but I didn't find
> any suitable one. Suggestions are welcome.

I didn't find anything either, but hopefully someone knows.

> As for implementation details, the one I posted was optimized for both
> speed and size, and at least in my opinion this bit array driven
> parametric implementation is exactly what is needed here (using a string
> of allowed characters with strchr-style lookups would bring much worse
> complexity, and checking the characters using series of hardcoded if
> conditions could quickly grow to more than those 16 bytes used by the
> array).

But is this really something which should be optimised? This is driver
initialisation, not in some hot path, right? Can you even measure the
difference?

-- 
Kalle Valo