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SubjectRe: [PATCH] mtd: mtd_oobtest: fix verify errors due to incorrect use of prandom_bytes_state()
From
2014/1/22 Lothar Waßmann <LW@karo-electronics.de>:
> 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@KARO-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;

I would rather fix the use of prandom_bytes_state() in write_eraseblock()
than fix in verify_eraseblock_in_one_go().

>> @@ -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;

The same goes for this. I would rather fix prandom_bytes_state() when
writing OOBs.
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