linux-kernel - Re: [PATCH] Open Firmware device tree virtual filesystem

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Date:	Sun, 31 Dec 2006 08:55:28 -1000
From:	Mitch Bradley <wmb@...mworks.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	"OLPC Developer's List" <devel@...top.org>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	Jim Gettys <jg@...top.org>
Subject: Re: [PATCH] Open Firmware device tree virtual filesystem

I made all the changes Pekka suggested, except:

> +               security = strncmp(propname, "security-", 9) == 0;
>> +               len = 0;
>
> Redundant assignment, no?
>
>> +               if (!security)
>> +                       (void)callofw("getproplen", 2, 1, node, 
>> propname, &len);
>
That assignment turns out not to be redundant.  If a security variable 
is recognized, you want the length to be 0 so as not to expose the 
password.  In that case the following "getproplen" call won't be executed.

That logic was adapted from the existing file fs/proc/devtree.c .  It 
turns out that the code there has a bug: You really want to look for 
just "security-password" ; there is no need to, and good reasons not to, 
suppress the length of "security-mode" and "security-#badlogins".  (Good 
OFW implementations won't leak the password length anyway, so check is 
only needed as a workaround).

I have rewritten the code for clarity and correctness thusly:

        if (strcmp(propname, "security-password") == 0) {
            len = 0;        /* Don't leak password length */
        } else {
            callofw("getproplen", 2, 1, node, propname, &len);
        }



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