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

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

[Jerome Glisse]

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@redhat.com wrote:
> From: Jérôme Glisse <jglisse@redhat.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@redhat.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> Cc: linux-kernel@vger.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
> 

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

[Andrew Morton]

On Wed, 10 Apr 2019 15:43:50 -0400 Jerome Glisse <jglisse@redhat.com> wrote:

> 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).

Looks good to me.

Minchan & Sergey, can you please review?


From: Jérôme Glisse <jglisse@redhat.com>
Subject: zram: pass down the bvec we need to read into in the work struct

When scheduling work item to read page we need to pass down the proper
bvec struct which points to the page to read into.  Before this patch it
uses a randomly initialized bvec (only if PAGE_SIZE != 4096) which is
wrong.

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).

Link: http://lkml.kernel.org/r/20190408183219.26377-1-jglisse@redhat.com
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/block/zram/zram_drv.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/block/zram/zram_drv.c~zram-pass-down-the-bvec-we-need-to-read-into-in-the-work-struct
+++ a/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 zr
 {
 	struct zram_work work;
 
+	work.bvec = *bvec;
 	work.zram = zram;
 	work.entry = entry;
 	work.bio = bio;
_

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

[Sergey Senozhatsky]

On (04/16/19 16:53), Andrew Morton wrote:
> > 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).
> 
> Looks good to me.
> 
> Minchan & Sergey, can you please review?

Sorry.

Looks OK to me.

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

	-ss