Subject: Re: [RFC PATCH net-next 7/9] ethtool: cmis_cdb: Add a layer for supporting CDB commands

From: Simon Horman <[email-masked]>
Date: Mon, 22 Jan 2024 10:31:00 +0000

On Mon, Jan 22, 2024 at 10:45:28AM +0200, Danielle Ratson wrote:

...

> +/**
> + * struct ethtool_cmis_cdb_request - CDB commands request fields as decribed in
> + *				the CMIS standard
> + * @id: Command ID.
> + * @epl_len: EPL memory length.
> + * @lpl_len: LPL memory length.
> + * @chk_code: Check code for the previous field and the payload.
> + * @resv1: Added to match the CMIS standard request continuity.
> + * @resv2: Added to match the CMIS standard request continuity.
> + * @payload: Payload for the CDB commands.
> + */
> +struct ethtool_cmis_cdb_request {
> +	__be16 id;
> +	struct_group(body,
> +		u16 epl_len;
> +		u8 lpl_len;
> +		u8 chk_code;
> +		u8 resv1;
> +		u8 resv2;
> +		u8 payload[ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH];
> +	);
> +};
> +
> +#define CDB_F_COMPLETION_VALID		BIT(0)
> +#define CDB_F_STATUS_VALID		BIT(1)
> +
> +/**
> + * struct ethtool_cmis_cdb_cmd_args - CDB commands execution arguments
> + * @req: CDB command fields as described in the CMIS standard.
> + * @max_duration: Maximum duration time for command completion in msec.
> + * @read_write_len_ext: Allowable additional number of byte octets to the LPL
> + *			in a READ or a WRITE commands.
> + * @rpl_exp_len: Expected reply length in bytes.
> + * @flags: Validation flags for CDB commands.
> + */
> +struct ethtool_cmis_cdb_cmd_args {
> +	struct ethtool_cmis_cdb_request req;
> +	u16				max_duration;
> +	u8				read_write_len_ext;
> +	u8                              rpl_exp_len;
> +	u8				flags;
> +};

...

> +int ethtool_cmis_page_init(struct ethtool_module_eeprom *page_data,
> +			   u8 page, u32 offset, u32 length)
> +{
> +	page_data->page = page;
> +	page_data->offset = offset;
> +	page_data->length = length;
> +	page_data->i2c_address = ETHTOOL_CMIS_CDB_PAGE_I2C_ADDR;
> +	page_data->data = kmalloc(page_data->length, GFP_KERNEL);
> +	if (!page_data->data)
> +		return -ENOMEM;
> +
> +	return 0;
> +}

...

> +static int
> +__ethtool_cmis_cdb_execute_cmd(struct net_device *dev,
> +			       struct ethtool_module_eeprom *page_data,
> +			       u32 offset, u32 length, void *data)
> +{
> +	const struct ethtool_ops *ops = dev->ethtool_ops;
> +	struct netlink_ext_ack extack = {};
> +	int err;
> +
> +	page_data->offset = offset;
> +	page_data->length = length;
> +
> +	memset(page_data->data, 0, ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH);
> +	memcpy(page_data->data, data, page_data->length);
> +
> +	err = ops->set_module_eeprom_by_page(dev, page_data, &extack);
> +	if (err < 0) {
> +		if (extack._msg)
> +			netdev_err(dev, "%s\n", extack._msg);
> +	}
> +
> +	return err;
> +}

...

> +int ethtool_cmis_cdb_execute_cmd(struct net_device *dev,
> +				 struct ethtool_cmis_cdb_cmd_args *args)
> +{
> +	struct ethtool_module_eeprom page_data = {};
> +	u32 offset;
> +	int err;
> +
> +	args->req.chk_code =
> +		cmis_cdb_calc_checksum(&args->req, sizeof(args->req));
> +
> +	if (args->req.lpl_len > args->read_write_len_ext) {
> +		ethnl_module_fw_flash_ntf_err(dev,
> +					      "LPL length is longer than CDB read write length extension allows");
> +		return -EINVAL;
> +	}
> +
> +	err = ethtool_cmis_page_init(&page_data, ETHTOOL_CMIS_CDB_CMD_PAGE, 0,
> +				     ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH);

ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH is passed as the length argument
of ethtool_cmis_page_init, which will allocate that many
bytes for page_data->data.

> +	if (err < 0)
> +		return err;
> +
> +	/* According to the CMIS standard, there are two options to trigger the
> +	 * CDB commands. The default option is triggering the command by writing
> +	 * the CMDID bytes. Therefore, the command will be split to 2 calls:
> +	 * First, with everything except the CMDID field and then the CMDID
> +	 * field.
> +	 */
> +	offset = CMIS_CDB_CMD_ID_OFFSET +
> +		offsetof(struct ethtool_cmis_cdb_request, body);
> +	err = __ethtool_cmis_cdb_execute_cmd(dev, &page_data, offset,
> +					     sizeof(args->req.body),
> +					     &args->req.body);

Hi Danielle,

However, here sizeof(args->req.body) is passed as the length
argument of __ethtool_cmis_cdb_execute_cmd() which will:

1. Zero ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH bytes of page_data->data
2. Copy sizeof(args->req.body) bytes into page_data->data

args->req.body includes several fields, one of which is
ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH bytes long. So,
args->req.body > ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH
and it seems that step 2 above causes a buffer overrun.

Flagged by clang-17 W=1 build

 In file included from net/ethtool/cmis_cdb.c:3:
 In file included from ./include/linux/ethtool.h:16:
 In file included from ./include/linux/bitmap.h:12:
 In file included from ./include/linux/string.h:295:
 ./include/linux/fortify-string.h:579:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
   579 |                         __write_overflow_field(p_size_field, size);
       |                         ^
 ./include/linux/fortify-string.h:579:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
 ./include/linux/fortify-string.h:579:4: error: call to '__write_overflow_field' declared with 'warning' attribute: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]

> +	if (err < 0)
> +		goto out;
> +
> +	offset = CMIS_CDB_CMD_ID_OFFSET +
> +		offsetof(struct ethtool_cmis_cdb_request, id);
> +	err = __ethtool_cmis_cdb_execute_cmd(dev, &page_data, offset,
> +					     sizeof(args->req.id),
> +					     &args->req.id);
> +	if (err < 0)
> +		goto out;
> +
> +	err = cmis_cdb_wait_for_completion(dev, args);
> +	if (err < 0)
> +		goto out;
> +
> +	err = cmis_cdb_wait_for_status(dev, args);
> +	if (err < 0)
> +		goto out;
> +
> +	err = cmis_cdb_process_reply(dev, &page_data, args);
> +
> +out:
> +	ethtool_cmis_page_fini(&page_data);
> +	return err;
> +}

...