linux-kernel - Re: [PATCH 1/6] lib/cmdline.c: Add backslash support to kernel commandline parsing.

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Date:   Fri, 15 Sep 2017 18:14:09 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Michal Suchanek <msuchanek@...e.de>
Cc:     Jonathan Corbet <corbet@....net>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jani Nikula <jani.nikula@...el.com>,
        Kamlakant Patel <kamlakant.patel@...adcom.com>,
        Bamvor Jian Zhang <bamvor.zhangjian@...aro.org>,
        Tamara Diaconita <diaconitatamara@...il.com>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Baoquan He <bhe@...hat.com>,
        Ilya Matveychikov <matvejchikov@...il.com>,
        Ingo Molnar <mingo@...nel.org>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/6] lib/cmdline.c: Add backslash support to kernel
 commandline parsing.

On Fri, Sep 15, 2017 at 07:02:46PM +0200, Michal Suchanek wrote:

>  	for (i = 0; args[i]; i++) {
> -		if (isspace(args[i]) && !in_quote)
> +		if (isspace(args[i]) && !in_quote && !backslash)
>  			break;
> -		if (equals == 0) {
> -			if (args[i] == '=')
> -				equals = i;
> +
> +		if ((equals == 0) && (args[i] == '='))
> +			equals = i;
> +
> +		if (!backslash) {
> +			if ((args[i] == '"') || (args[i] == '\\')) {
> +				if (args[i] == '"')
> +					in_quote = !in_quote;
> +				if (args[i] == '\\')
> +					backslash = 1;
> +
> +				memmove(args + 1, args, i);
> +				args++;
> +				i--;
> +			}
> +		} else {
> +			backslash = 0;
>  		}
> -		if (args[i] == '"')
> -			in_quote = !in_quote;
>  	}

... and that makes for Unidiomatic Work With Strings Award for this September.
Using memmove() for string rewrite is almost always bad taste; in this case
it's also (as usual) broken.