linux-kernel - Re: [PATCH] zram: fix possible use after free in zcomp

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Message-ID: <20150907125343.GG10075@ares>
Date:	Mon, 7 Sep 2015 13:53:43 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zram: fix possible use after free in zcomp_create()

On Mon, Sep 07, 2015 at 08:11:48PM +0900, Sergey Senozhatsky wrote:
> On (09/07/15 11:33), Luis Henriques wrote:
> > zcomp_create() verifies the success of zcomp_strm_{multi,siggle}_create()
> > through comp->stream, which can potentially be pointing to memory that was
> > freed if these functions returned an error.
> > 
> 
> good catch.
> 
> we probably better start checking the zcomp_strm_multi_create()/
> zcomp_strm_single_create() status in zcomp_create(); that's much
> more obvious and that's why we return it in the first place.
> 
> what do you think?
>

Yep, that's probably a better solution.

Acked-by: Luis Henriques <luis.henriques@...onical.com>

Cheers,
--
Luís

> ---
> 
>  drivers/block/zram/zcomp.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> index 3456d5a..16bbc8c 100644
> --- a/drivers/block/zram/zcomp.c
> +++ b/drivers/block/zram/zcomp.c
> @@ -360,6 +360,7 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
>  {
>  	struct zcomp *comp;
>  	struct zcomp_backend *backend;
> +	int ret;
>  
>  	backend = find_backend(compress);
>  	if (!backend)
> @@ -371,10 +372,10 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
>  
>  	comp->backend = backend;
>  	if (max_strm > 1)
> -		zcomp_strm_multi_create(comp, max_strm);
> +		ret = zcomp_strm_multi_create(comp, max_strm);
>  	else
> -		zcomp_strm_single_create(comp);
> -	if (!comp->stream) {
> +		ret = zcomp_strm_single_create(comp);
> +	if (ret != 0) {
>  		kfree(comp);
>  		return ERR_PTR(-ENOMEM);
>  	}
> 
--
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