Re: [PATCH] Open Firmware device tree virtual filesystem

From: Mitch Bradley
Date: Sun Dec 31 2006 - 13:56:17 EST

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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