linux-kernel - Re: [PATCH 1/3] drivers: staging: wilc1000: Check for errors before kfree

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Message-ID: <20151002133911.GP7289@mwanda>
Date:	Fri, 2 Oct 2015 16:39:11 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Chandra S Gorentla <csgorentla@...il.com>
Cc:	gregkh@...uxfoundation.org, rachel.kim@...el.com,
	devel@...verdev.osuosl.org, chris.park@...el.com,
	linux-wireless@...r.kernel.org, johnny.kim@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] drivers: staging: wilc1000: Check for errors before
 kfree

On Fri, Oct 02, 2015 at 06:47:35PM +0530, Chandra S Gorentla wrote:
> During the clean-up of the function, it is need to check if
> errors occurred, not the memory pointer.
>

The bug here is that we have a use after free on the success path.  It
should have been mentioned in the changelog.

Anyway, this patch is buggy.  If result == -EFAULT then it will crash.
Also this patch is really ugly.  There is someone who is going to send a
correct fix (just add a return 0).

This driver usese "do everything" style error handling.  It is a bug
prone anti-pattern because doing everything is more complicated than
doing one thing.  You can easily see it is bug prone, because it made
you introduce a bug, right?

Instead the error handling should look like this:

	return 0;

err_free_msg:
	kfree(pstrMessage);

	return ret;

There are no error paths where we need to free "pstrMessage->pvBuffer"
but if we were to add one it would look like this:

	return 0;

err_pvbuffer:
	kfree(pstrMessage->pvBuffer);
err_msg:
	kfree(pstrMessage);

	return ret;

This is a minimal, uncomplicated, no indenting, no if statement way of
unwinding.

regards,
dan carpenter

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