linux-kernel - Re: [PATCH 4/9] mtd: nand: qcom: fix null pointer access for erased buffer detection

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Message-ID: <d201308d57317ff7d37d7169d7985d76@codeaurora.org>
Date:   Thu, 12 Apr 2018 12:24:16 +0530
From:   Abhishek Sahu <absahu@...eaurora.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Archit Taneja <architt@...eaurora.org>,
        Richard Weinberger <richard@....at>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Andy Gross <andy.gross@...aro.org>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 4/9] mtd: nand: qcom: fix null pointer access for erased
 buffer detection

On 2018-04-10 14:42, Miquel Raynal wrote:
> Hi Abhishek,
> 
> On Wed,  4 Apr 2018 18:12:20 +0530, Abhishek Sahu
> <absahu@...eaurora.org> wrote:
> 
>> parse_read_errors can be called with only oob buf also in which
>> case data_buf will be NULL.  If data_buf is NULL, then don’t
>> treat this page as completely erased in case of ECC uncorrectable
>> error.
>> 
>> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
>> ---
>>  drivers/mtd/nand/qcom_nandc.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/mtd/nand/qcom_nandc.c 
>> b/drivers/mtd/nand/qcom_nandc.c
>> index 57c16a6..0ebcc55 100644
>> --- a/drivers/mtd/nand/qcom_nandc.c
>> +++ b/drivers/mtd/nand/qcom_nandc.c
>> @@ -1607,9 +1607,11 @@ static int parse_read_errors(struct 
>> qcom_nand_host *host, u8 *data_buf,
>>  			if (host->bch_enabled) {
>>  				erased = (erased_cw & ERASED_CW) == ERASED_CW ?
>>  					 true : false;
> 
> Why the parse_read_errors() function could not be called without
> data_buf when using BCH? Are you sure the situation can only happen
> without it?
> 

   host->bch_enabled case is different where controller itself tells
   regarding erased page in status register.

> Would the following apply here too, with a:
> 

  erased_chunk_check_and_fixup will be used only for 4 bit RS ECC
  code in which there is no support from HW for erased page detection
  and we need to check few data bytes value.

  Thanks,
  Abhishek

> if (!data_buf) {
>         erased = false;
> } else {
>         if (host->bch_enabled)
>                 ...
>         else
>                 ...
> }
> 
>> -			} else {
>> +			} else if (data_buf) {
>>  				erased = erased_chunk_check_and_fixup(data_buf,
>>  								      data_len);
>> +			} else {
>> +				erased = false;
>>  			}
>> 
>>  			if (erased) {
>> @@ -1652,7 +1654,8 @@ static int parse_read_errors(struct 
>> qcom_nand_host *host, u8 *data_buf,
>>  			max_bitflips = max(max_bitflips, stat);
>>  		}
>> 
>> -		data_buf += data_len;
>> +		if (data_buf)
>> +			data_buf += data_len;
>>  		if (oob_buf)
>>  			oob_buf += oob_len + ecc->bytes;
>>  	}
> 
> Thanks,
> Miquèl