linux-kernel - Re: [PATCH] hw_random: free rng

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Date:	Sun, 17 Mar 2013 02:14:52 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Satoru Takeuchi <satoru.takeuchi@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Aurelien Jarno <aurelien@...el32.net>,
	Matt Mackall <mpm@...enic.com>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH] hw_random: free rng_buffer at module exit

On Fri, 2013-03-15 at 15:35 +1030, Rusty Russell wrote:
> Satoru Takeuchi <satoru.takeuchi@...il.com> writes:
> > At Thu, 14 Mar 2013 17:11:21 +1030,
> > Rusty Russell wrote:
> >> 
> >> Satoru Takeuchi <satoru.takeuchi@...il.com> writes:
> >> > Hi Rusty,
> >> >
> >> > At Tue, 12 Mar 2013 15:43:33 -0700,
> >> > Greg Kroah-Hartman wrote:
> >> >> @@ -307,6 +312,14 @@ int hwrng_register(struct hwrng *rng)
> >> >>  
> >> >>  	mutex_lock(&rng_mutex);
> >> >>  
> >> >> +	/* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
> >> >> +	err = -ENOMEM;
> >> >> +	if (!rng_buffer) {
> >> >> +		rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
> >> >
> >> > rng_buffer is now kmalloc-ed, but not kfree-ed. Shoudn't it be kfree-ed
> >> > at hwrng_unregister()? If my suspect is correct, the same problem is
> >> > in 3.8.3-rc1 and 3.0.69-rc1. I'm OK to make a patch, but it'll be after
> >> > some hours.
> >> >
> >> > Corecct me if I'm wrong.
> >> 
> >> Yes, it would be nice to free it, but it really makes sense to free it
> >> in module_cleanup() (which would have to be written, as the module
> >> currently doesn't have one).
> >> 
> >> Cheers,
> >> Rusty.
> >
> > From: Satoru Takeuchi <satoru.takeuchi@...il.com>
> >
> > rng-core module allocates rng_buffer by kmalloc() since commit
> > f7f154f1246ccc5a0a7e9ce50932627d60a0c878. But this buffer won't be
> > freed and there is a memory leak possibility at module exit.
> >
> > Signed-off-by: Satoru Takeuchi <satoru.takeuchi@...il.com>
> > Cc: Rusty Russell <rusty@...tcorp.com.au>
> > Cc: Matt Mackall <mpm@...enic.com>
> > Cc: Herbert Xu <herbert@...dor.apana.org.au>
> > Cc: Aurelien Jarno <aurelien@...el32.net>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: stable@...r.kernel.org
> 
> Cc: stable might be overkill, but I've tested it and put it in my patch
> queue, and will push it to Linus once it's survived linux-next.

If the module cannot be removed currently, it does not leak.  Making it
removable is a feature addition and I think you're right that it's not
suitable for stable.

Ben.

-- 
Ben Hutchings
Usenet is essentially a HUGE group of people passing notes in class.
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