linux-kernel - Re: [PATCH 2/7] mtd: spi-nor: fix iteration over smpt array

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Date:   Thu, 8 Nov 2018 13:50:38 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     <Tudor.Ambarus@...rochip.com>
Cc:     <marek.vasut@...il.com>, <dwmw2@...radead.org>,
        <computersforpeace@...il.com>, <richard@....at>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <yogeshnarayan.gaur@....com>, <cyrille.pitchen@...ev4u.fr>
Subject: Re: [PATCH 2/7] mtd: spi-nor: fix iteration over smpt array

On Thu, 8 Nov 2018 11:07:09 +0000
<Tudor.Ambarus@...rochip.com> wrote:

> Iterate over smpt array using its starting address and length
> instead of the blindly iterations that used data found in the array.

		 ^blind

> 
> This prevents possible memory accesses outside of the smpt array
> boundaries in case software, or manufacturers, misrepresent smpt
> array fields.
> 
> Suggested-by: Boris Brezillon <boris.brezillon@...tlin.com>
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>

I think we should consider this patch as a fix. Would you mind adding a
Fixes tag?

> ---
>  drivers/mtd/spi-nor/spi-nor.c | 39 +++++++++++++++++++++++++++++----------
>  1 file changed, 29 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 2cdf96013689..59dcedb08691 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -2860,12 +2860,15 @@ static u8 spi_nor_smpt_read_dummy(const struct spi_nor *nor, const u32 settings)
>   * spi_nor_get_map_in_use() - get the configuration map in use
>   * @nor:	pointer to a 'struct spi_nor'
>   * @smpt:	pointer to the sector map parameter table
> + * @smpt_len:	sector map parameter table length
>   */
> -static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt)
> +static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt,
> +					 u8 smpt_len)
>  {
>  	const u32 *ret = NULL;
> -	u32 i, addr;
> +	u32 addr;
>  	int err;
> +	u8 i;
>  	u8 addr_width, read_opcode, read_dummy;
>  	u8 read_data_mask, data_byte, map_id;
>  
> @@ -2874,9 +2877,10 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt)
>  	read_opcode = nor->read_opcode;
>  
>  	map_id = 0;
> -	i = 0;
>  	/* Determine if there are any optional Detection Command Descriptors */
> -	while (!(smpt[i] & SMPT_DESC_TYPE_MAP)) {
> +	for (i = 0; i < smpt_len; i += 2) {
> +		if (smpt[i] & SMPT_DESC_TYPE_MAP)
> +			break;

nit: add a blank line here.

>  		read_data_mask = SMPT_CMD_READ_DATA(smpt[i]);
>  		nor->addr_width = spi_nor_smpt_addr_width(nor, smpt[i]);
>  		nor->read_dummy = spi_nor_smpt_read_dummy(nor, smpt[i]);
> @@ -2892,18 +2896,33 @@ static const u32 *spi_nor_get_map_in_use(struct spi_nor *nor, const u32 *smpt)
>  		 * Configuration that is currently in use.
>  		 */
>  		map_id = map_id << 1 | !!(data_byte & read_data_mask);
> -		i = i + 2;
>  	}
>  
> -	/* Find the matching configuration map */
> -	while (SMPT_MAP_ID(smpt[i]) != map_id) {
> +	/*
> +	 * If command descriptors are provided, they always precede map
> +	 * descriptors in the table. There is no need to start the iteration
> +	 * over smpt array all over again.
> +	 *
> +	 * Find the matching configuration map.
> +	 */
> +	while (i < smpt_len) {
> +		if (SMPT_MAP_ID(smpt[i]) == map_id) {
> +			ret = smpt + i;
> +			break;
> +		}
> +
> +		/*
> +		 * If there are no more configuration map descriptors and no
> +		 * configuration ID matched the configuration identifier, the
> +		 * sector address map is unknown.
> +		 */
>  		if (smpt[i] & SMPT_DESC_END)
> -			goto out;
> +			break;
> +
>  		/* increment the table index to the next map */
>  		i += SMPT_MAP_REGION_COUNT(smpt[i]) + 1;
>  	}
>  
> -	ret = smpt + i;
>  	/* fall through */
>  out:
>  	nor->addr_width = addr_width;
> @@ -3025,7 +3044,7 @@ static int spi_nor_parse_smpt(struct spi_nor *nor,
>  	for (i = 0; i < smpt_header->length; i++)
>  		smpt[i] = le32_to_cpu(smpt[i]);
>  
> -	sector_map = spi_nor_get_map_in_use(nor, smpt);
> +	sector_map = spi_nor_get_map_in_use(nor, smpt, smpt_header->length);
>  	if (!sector_map) {
>  		ret = -EINVAL;
>  		goto out;