linux-kernel - Re: [PATCH] zram: pass down the bvec we need to read into in the work struct

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Date:   Wed, 10 Apr 2019 15:43:50 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        stable@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] zram: pass down the bvec we need to read into in the
 work struct

Adding more Cc and stable (i thought this was 5.1 addition). Note that
without this patch on arch/kernel where PAGE_SIZE != 4096 userspace
could read random memory through a zram block device (thought userspace
probably would have no control on the address being read).

On Mon, Apr 08, 2019 at 02:32:19PM -0400, jglisse@...hat.com wrote:
> From: Jérôme Glisse <jglisse@...hat.com>
> 
> When scheduling work item to read page we need to pass down the proper
> bvec struct which point to the page to read into. Before this patch it
> uses randomly initialized bvec (only if PAGE_SIZE != 4096) which is
> wrong.
> 
> Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Nitin Gupta <ngupta@...are.org>
> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
> Cc: linux-kernel@...r.kernel.org
> ---
>  drivers/block/zram/zram_drv.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 399cad7daae7..d58a359a6622 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -774,18 +774,18 @@ struct zram_work {
>  	struct zram *zram;
>  	unsigned long entry;
>  	struct bio *bio;
> +	struct bio_vec bvec;
>  };
>  
>  #if PAGE_SIZE != 4096
>  static void zram_sync_read(struct work_struct *work)
>  {
> -	struct bio_vec bvec;
>  	struct zram_work *zw = container_of(work, struct zram_work, work);
>  	struct zram *zram = zw->zram;
>  	unsigned long entry = zw->entry;
>  	struct bio *bio = zw->bio;
>  
> -	read_from_bdev_async(zram, &bvec, entry, bio);
> +	read_from_bdev_async(zram, &zw->bvec, entry, bio);
>  }
>  
>  /*
> @@ -798,6 +798,7 @@ static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
>  {
>  	struct zram_work work;
>  
> +	work.bvec = *bvec;
>  	work.zram = zram;
>  	work.entry = entry;
>  	work.bio = bio;
> -- 
> 2.20.1
>