Re: [PATCH v2 4/4] HID: i2c-hid: fix i2c_hid_get_raw_report count mismatches

Jean Delvare
2012-12-05T19:59:26Z

On Wed, 5 Dec 2012 15:02:56 +0100, Benjamin Tissoires wrote:
> The previous memcpy implementation relied on the size advertized by the
> device. There were no guarantees that buf was big enough.
>
> Some gymnastic is also required with the +2/-2 to take into account
> the first 2 bytes of the returned buffer where the total returned
> length is supplied by the device.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
> ---
> drivers/hid/i2c-hid/i2c-hid.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
> index c6630d4..ce01d59 100644
> --- a/drivers/hid/i2c-hid/i2c-hid.c
> +++ b/drivers/hid/i2c-hid/i2c-hid.c
> @@ -502,23 +502,31 @@ static int i2c_hid_get_raw_report(struct hid_device *hid,
> {
> struct i2c_client *client = hid->driver_data;
> struct i2c_hid *ihid = i2c_get_clientdata(client);
> + size_t ret_count, ask_count;
> int ret;
>
> if (report_type == HID_OUTPUT_REPORT)
> return -EINVAL;
>
> - if (count > ihid->bufsize)
> - count = ihid->bufsize;
> + /* +2 bytes to include the size of the reply in the query buffer */
> + ask_count = min(count + 2, (size_t)ihid->bufsize);
>
> ret = i2c_hid_get_report(client,
> report_type == HID_FEATURE_REPORT ? 0x03 : 0x01,
> - report_number, ihid->inbuf, count);
> + report_number, ihid->inbuf, ask_count);
>
> if (ret < 0)
> return ret;
>
> - count = ihid->inbuf[0] | (ihid->inbuf[1] << 8);
> + ret_count = ihid->inbuf[0] | (ihid->inbuf[1] << 8);
>
> + if (!ret_count)

I'd make this (ret_count <= 2), as this would let you call memcpy with a
null or even negative length.

Other than that, the new code looks OK and safe.

> + return 0;
> +
> + ret_count = min(ret_count, ask_count);
> +
> + /* The query buffer contains the size, dropping it in the reply */
> + count = min(count, ret_count - 2);
> memcpy(buf, ihid->inbuf + 2, count);
>
> return count;

--
Jean Delvare