linux-kernel - Re: [PATCH] mtd: mtd_oobtest: fix verify errors due to incorrect use of prandom_bytes

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Date:	Wed, 22 Jan 2014 15:09:59 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Lothar Waßmann <LW@...O-electronics.de>
Cc:	linux-mtd@...ts.infradead.org,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
	Akinobu Mita <akinobu.mita@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Huang Shijie <b32955@...escale.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: mtd_oobtest: fix verify errors due to incorrect
 use of prandom_bytes_state()

Hi,

Is anyone taking care of this?

Lothar Waßmann wrote:
> When using prandom_bytes_state() it is critical to use the same block
> size in all invocations that are to produce the same random sequence.
> Otherwise the state of the PRNG will be out of sync if the blocksize
> is not divisible by 4.
> This leads to bogus verification errors in several tests which use
> different block sizes to initialize the buffer for writing and
> comparison.
> 
> Signed-off-by: Lothar Waßmann <LW@...O-electronics.de>
> ---
>  drivers/mtd/tests/oobtest.c |   14 ++++++++++++--
>  1 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/tests/oobtest.c b/drivers/mtd/tests/oobtest.c
> index 2e9e2d1..72c7359 100644
> --- a/drivers/mtd/tests/oobtest.c
> +++ b/drivers/mtd/tests/oobtest.c
> @@ -213,8 +213,15 @@ static int verify_eraseblock_in_one_go(int ebnum)
>  	int err = 0;
>  	loff_t addr = ebnum * mtd->erasesize;
>  	size_t len = mtd->ecclayout->oobavail * pgcnt;
> +	int i;
> +
> +	for (i = 0; i < pgcnt; i++)
> +		prandom_bytes_state(&rnd_state, &writebuf[i * use_len],
> +				use_len);
> +	if (len % use_len)
> +		prandom_bytes_state(&rnd_state, &writebuf[i * use_len],
> +				len % use_len);
>  
> -	prandom_bytes_state(&rnd_state, writebuf, len);
>  	ops.mode      = MTD_OPS_AUTO_OOB;
>  	ops.len       = 0;
>  	ops.retlen    = 0;
> @@ -594,7 +601,10 @@ static int __init mtd_oobtest_init(void)
>  		if (bbt[i] || bbt[i + 1])
>  			continue;
>  		prandom_bytes_state(&rnd_state, writebuf,
> -					mtd->ecclayout->oobavail * 2);
> +					mtd->ecclayout->oobavail);
> +		prandom_bytes_state(&rnd_state,
> +					writebuf + mtd->ecclayout->oobavail,
> +					mtd->ecclayout->oobavail);
>  		addr = (i + 1) * mtd->erasesize - mtd->writesize;
>  		ops.mode      = MTD_OPS_AUTO_OOB;
>  		ops.len       = 0;


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