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

[Cristian Marussi <cristian.marussi@arm.com>]

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);
+		if (calc_list_sz != real_list_sz) {
+			dev_err(dev,
+				"Malformed reply - real_sz:%zd  calc_sz:%u\n",
+				real_list_sz, calc_list_sz);
+			ret = -EPROTO;
+			break;
+		}
+
 		for (loop = 0; loop < loop_num_ret; loop++)
 			protocols_imp[tot_num_ret + loop] = *(list + loop);
 
-- 
2.32.0