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

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Message-ID: <20150907133332.GA539@swordfish>
Date:	Mon, 7 Sep 2015 22:33:32 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Luis Henriques <luis.henriques@...onical.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	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 (09/07/15 13:53), Luis Henriques 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>
> 

Oh, thanks. I don't mind if you will re-submit it; I just did minor
changes to our fix. Or I can handle it. I'm OK with either way. Btw,
did you hit that problem or you reviewed the code?

	-ss

> 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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