linux-kernel - Re: [PATCH v3] zram: fix possible use after free in zcomp

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Date:	Tue, 8 Sep 2015 19:27:11 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Luis Henriques <luis.henriques@...onical.com>,
	Minchan Kim <minchan@...nel.org>, linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH v3] zram: fix possible use after free in zcomp_create()

On (09/08/15 18:56), Sergey Senozhatsky wrote:
> On (09/08/15 10:39), 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.
> > 
> > While at it, replace a 'ERR_PTR(-ENOMEM)' by a more generic
> > 'ERR_PTR(error)' as in the future zcomp_strm_{multi,siggle}_create() could
> > return other error codes.  Function documentation updated accordingly.
> > 

Oh...forgot to Cc Andrew
Andrew, please disregard V2 of this patch.

V3
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

	-ss

> > ---
> > 
> > Changes since v2:
> >  * Renamed local variable 'ret' to 'error'
> >  * Usage of 'ERR_PTR(error)' to accommodate future error codes returned by
> >    zcomp_strm_{multi,siggle}_create
> >  (all suggested by Minchan)
> > 
> > Changes since v1:
> >  * Check zcomp_strm_{multi,siggle}_create() return code instead
> >    comp->stream (suggested by Sergey)
> > 
> > drivers/block/zram/zcomp.c | 12 +++++++-----
> >  1 file changed, 7 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> > index 965d1afb0eaa..5cb13ca3a3ac 100644
> > --- a/drivers/block/zram/zcomp.c
> > +++ b/drivers/block/zram/zcomp.c
> > @@ -330,12 +330,14 @@ void zcomp_destroy(struct zcomp *comp)
> >   * allocate new zcomp and initialize it. return compressing
> >   * backend pointer or ERR_PTR if things went bad. ERR_PTR(-EINVAL)
> >   * if requested algorithm is not supported, ERR_PTR(-ENOMEM) in
> > - * case of allocation error.
> > + * case of allocation error, or any other error potentially
> > + * returned by functions zcomp_strm_{multi,single}_create.
> >   */
> >  struct zcomp *zcomp_create(const char *compress, int max_strm)
> >  {
> >  	struct zcomp *comp;
> >  	struct zcomp_backend *backend;
> > +	int error;
> >  
> >  	backend = find_backend(compress);
> >  	if (!backend)
> > @@ -347,12 +349,12 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
> >  
> >  	comp->backend = backend;
> >  	if (max_strm > 1)
> > -		zcomp_strm_multi_create(comp, max_strm);
> > +		error = zcomp_strm_multi_create(comp, max_strm);
> >  	else
> > -		zcomp_strm_single_create(comp);
> > -	if (!comp->stream) {
> > +		error = zcomp_strm_single_create(comp);
> > +	if (error) {
> >  		kfree(comp);
> > -		return ERR_PTR(-ENOMEM);
> > +		return ERR_PTR(error);
> >  	}
> >  	return comp;
> >  }
> > 
> 
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