linux-kernel - Re: [patch] [bugfix] loop.c

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Message-ID: <Pine.LNX.4.64.0703240011420.29565@twin.jikos.cz>
Date:	Sat, 24 Mar 2007 00:18:10 +0100 (CET)
From:	Jiri Kosina <jikos@...os.cz>
To:	Michael Tokarev <mjt@....msk.ru>
cc:	Eric Dumazet <dada1@...mosbay.com>, Tomas M <tomas@...x.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] [bugfix] loop.c

On Fri, 23 Mar 2007, Michael Tokarev wrote:

> Speaking of which, I wonder...  Here, and in many other places.
> If some variable is marked as MODULE_PARAM (or whatever it is called 
> nowadays), used in module init routine, AND subsequently used for 
> various bound checks and loops...
[...]
> and so on.  Together with:
>   # modprobe foo n=10
>   # echo 20 > /sys/module/foo/parameters/n
> After that, we have 10 entries in mem[], and n is equal to 20, so the 
> for-loop above will be up to i=19.  Which will reference unallocated 
> memory.... Amd I dreaming?

This can be solved either by using module_param_call() in every module, 
and properly handling the "asynchronous" changes of module parameter, or 
by just disallowing the parameter from being tuned through sysfs 
completely (by setting the 'permissions' parameter of module_param() to 
zero ... which is what many drivers do anyway, I'd guess).

-- 
Jiri Kosina
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