Re: [PATCH 04/22] firmware: arm_scmi: Validate BASE_DISCOVER_LIST_PROTOCOLS reply

Sudeep Holla
2022-04-28T10:19:49Z

On Wed, Mar 30, 2022 at 04:05:33PM +0100, Cristian Marussi wrote:
> Do not blindly trust SCMI backend server reply about list of implemented
> protocols, instead validate the reported length of the list of protocols
> against the real payload size of the message reply.
>
> Fixes: b6f20ff8bd9 ("firmware: arm_scmi: add common infrastructure and support for base protocol")
> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> ---
> drivers/firmware/arm_scmi/base.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/drivers/firmware/arm_scmi/base.c b/drivers/firmware/arm_scmi/base.c
> index f279146f8110..c1165d1282ef 100644
> --- a/drivers/firmware/arm_scmi/base.c
> +++ b/drivers/firmware/arm_scmi/base.c
> @@ -189,6 +189,9 @@ scmi_base_implementation_list_get(const struct scmi_protocol_handle *ph,
> list = t->rx.buf + sizeof(*num_ret);
>
> do {
> + size_t real_list_sz;
> + u32 calc_list_sz;
> +
> /* Set the number of protocols to be skipped/already read */
> *num_skip = cpu_to_le32(tot_num_ret);
>
> @@ -202,6 +205,24 @@ scmi_base_implementation_list_get(const struct scmi_protocol_handle *ph,
> break;
> }
>
> + if (t->rx.len < (sizeof(u32) * 2)) {
> + dev_err(dev, "Truncated reply - rx.len:%zd\n",
> + t->rx.len);
> + ret = -EPROTO;
> + break;
> + }
> +
> + real_list_sz = t->rx.len - sizeof(u32);
> + calc_list_sz = ((loop_num_ret / sizeof(u32)) +
> + !!(loop_num_ret % sizeof(u32))) * sizeof(u32);

Any reason this can't be (loop_num_ret - 1) / sizeof(u32) + 1 ?

--
Regards,
Sudeep