linux-kernel - Re: [PATCH] usermodehelper: Fix -ENOMEM return logic

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Date:	Mon, 25 Feb 2013 15:05:14 +0000
From:	David Howells <dhowells@...hat.com>
To:	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	James Morris <james.l.morris@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] usermodehelper: Fix -ENOMEM return logic


Lucas De Marchi <lucas.demarchi@...fusion.mobi> wrote:

> Callers of call_usermodehelper_fns() should check the return value and
> free themselves the data passed if the return is -ENOMEM. This is
> because the subprocess_info is allocated in this function, and if the
> allocation fail, the cleanup function cannot be called.
> 
> However call_usermodehelper_exec() may also return -ENOMEM, in which
> case the cleanup function is called. This means that if the caller
> checked the return code, it was risking running the cleanup twice (like
> kernel/sys.c:orderly_poweroff()) and if not, a leak could happen.
> 
> This patch fixes both call_usermodehelper_fns() to never call the
> cleanup function in case retval == -ENOMEM and also the callers to
> actually check the return value of this function.

I suspect it's probably better to always call the cleanup function from
call_usermodehelper_fns() rather than have the cleanup done by the caller in
some circumstances and not others - would it make sense to change the cleanup
function to take the pointer to the caller data rather than to take the
subprocess_info struct?

David
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