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

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Date:   Wed, 8 Mar 2017 08:58:02 +0100
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Hannes Reinecke <hare@...e.de>, Jens Axboe <axboe@...com>,
        Nitin Gupta <ngupta@...are.org>,
        Christoph Hellwig <hch@....de>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        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

On 03/08/2017 06:11 AM, Minchan Kim wrote:
> And could you test this patch? It avoids split bio so no need new bio
> allocations and makes zram code simple.
> 
> From f778d7564d5cd772f25bb181329362c29548a257 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@...nel.org>
> Date: Wed, 8 Mar 2017 13:35:29 +0900
> Subject: [PATCH] fix
> 
> Not-yet-Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---

[...]

Yup, this works here.

I did a mkfs.xfs /dev/nvme0n1
dd if=/dev/urandom of=/test.bin bs=1M count=128
sha256sum test.bin
mount /dev/nvme0n1 /dir
mv test.bin /dir/
sha256sum /dir/test.bin

No panics and sha256sum of the 128MB test file still matches

Tested-by: Johannes Thumshirn <jthumshirn@...e.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>

Now that you removed the one page limit in zram_bvec_rw() you can also
add this hunk to remove the queue splitting:

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 85f4df8..27b168f6 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -868,8 +868,6 @@ static blk_qc_t zram_make_request(struct
request_queue *queue, struct bio *bio)
 {
        struct zram *zram = queue->queuedata;

-       blk_queue_split(queue, &bio, queue->bio_split);
-
        if (!valid_io_request(zram, bio->bi_iter.bi_sector,
                                        bio->bi_iter.bi_size)) {
                atomic64_inc(&zram->stats.invalid_io);

Byte,
	Johannes

-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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