linux-kernel - Re: [PATCH] zram: set physical queue limits to avoid array out of bounds accesses

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Date:   Tue, 7 Mar 2017 14:22:42 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Johannes Thumshirn <jthumshirn@...e.de>
Cc:     Jens Axboe <axboe@...com>, Nitin Gupta <ngupta@...are.org>,
        Christoph Hellwig <hch@....de>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Hannes Reinecke <hare@...e.de>, yizhan@...hat.com,
        Linux Block Layer Mailinglist <linux-block@...r.kernel.org>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] zram: set physical queue limits to avoid array out of
 bounds accesses

Hello Johannes,

On Mon, Mar 06, 2017 at 11:23:35AM +0100, Johannes Thumshirn wrote:
> zram can handle at most SECTORS_PER_PAGE sectors in a bio's bvec. When using
> the NVMe over Fabrics loopback target which potentially sends a huge bulk of
> pages attached to the bio's bvec this results in a kernel panic because of
> array out of bounds accesses in zram_decompress_page().

First of all, thanks for the report and fix up!
Unfortunately, I'm not familiar with that interface of block layer.

It seems this is a material for stable so I want to understand it clear.
Could you say more specific things to educate me?

What scenario/When/How it is problem?  It will help for me to understand!

Thanks.

> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> ---
>  drivers/block/zram/zram_drv.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index e27d89a..dceb5ed 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1189,6 +1189,8 @@ static int zram_add(void)
>  	blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
>  	blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);
>  	zram->disk->queue->limits.discard_granularity = PAGE_SIZE;
> +	zram->disk->queue->limits.max_sectors = SECTORS_PER_PAGE;
> +	zram->disk->queue->limits.chunk_sectors = 0;
>  	blk_queue_max_discard_sectors(zram->disk->queue, UINT_MAX);
>  	/*
>  	 * zram_bio_discard() will clear all logical blocks if logical block
> -- 
> 1.8.5.6
>