netdev - Re: [PATCH] drivers/net/wimax/i2400m/fw.c fix possible double free

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Date:	Wed, 17 Mar 2010 15:10:41 -0700
From:	Inaky Perez-Gonzalez <inaky.perez-gonzalez@...el.com>
To:	Darren Jenkins <darrenrjenkins@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	linux-wimax <linux-wimax@...el.com>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
	"Kao, Cindy H" <cindy.h.kao@...el.com>,
	"Brandewie, Dirk J" <dirk.j.brandewie@...el.com>,
	"wimax@...uxwimax.org" <wimax@...uxwimax.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers/net/wimax/i2400m/fw.c fix possible double free

On Wed, 2010-03-17 at 05:40 -0700, Darren Jenkins wrote: 
> On Wed, Mar 17, 2010 at 8:14 AM, David Miller <davem@...emloft.net>
> wrote:
> 
> > Therefore the krealloc() failure handling in this driver should NULL
> > out i2400m->fw_hdrs and that will fix the double kfree problem as well
> > as trap any stray references.
> 
> Yes that is a much better Idea. Thanks for the advice. 
> It also fixes the i2400m_barker_db problem that I didn't notice before.
> 
> 
> Fix double free on krealloc() failure by zeroing pointer

If krealloc() fails to aallocate a new pointer, the old block is
unmodified, so by doing this you are leaking a buffer allocation.

I think this should be solved at the site where i2400m_zrealloc_2x() is
called, with a 

if (result < 0) {
kfree(i2400m->fw_hdrs);
i2400m->fw_hdrs = NULL;
goto error_zrealloc;
}

or any other better fix. I am hesitant of having zrealloc_2x free the
original pointer because it breaks the traditional semantics that come
along being called 'realloc' (realloc if successful, keep the original
if not).

Am I missing anything?


> coverity CID: 13455
> 
> Signed-off-by: Darren Jenkins <darrenrjenkins@...il.com>
> ---
>  drivers/net/wimax/i2400m/fw.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wimax/i2400m/fw.c b/drivers/net/wimax/i2400m/fw.c
> index 25c24f0..9f3b594 100644
> --- a/drivers/net/wimax/i2400m/fw.c
> +++ b/drivers/net/wimax/i2400m/fw.c
> @@ -232,8 +232,9 @@ int i2400m_zrealloc_2x(void **ptr, size_t *_count, size_t el_size,
>  		*_count = new_count;
>  		*ptr = nptr;
>  		return 0;
> -	} else
> -		return -ENOMEM;
> +	}
> +	*ptr = NULL;
> +	return -ENOMEM;
>  }
>  
> 



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