firmware: arm_scmi: Fix list protocols enumeration in the base protocol

[ Upstream commit 8009120e0354a67068e920eb10dce532391361d0 ]

While enumerating protocols implemented by the SCMI platform using
BASE_DISCOVER_LIST_PROTOCOLS, the number of returned protocols is
currently validated in an improper way since the check employs a sum
between unsigned integers that could overflow and cause the check itself
to be silently bypassed if the returned value 'loop_num_ret' is big
enough.

Fix the validation avoiding the addition.

Link: https://lore.kernel.org/r/20220330150551.2573938-4-cristian.marussi@arm.com
Fixes: b6f20ff8bd94 ("firmware: arm_scmi: add common infrastructure and support for base protocol")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/firmware/arm_scmi/base.c b/drivers/firmware/arm_scmi/base.c
index f521933..3fe172c 100644 (file)
--- a/drivers/firmware/arm_scmi/base.c
+++ b/drivers/firmware/arm_scmi/base.c
@@ -197,7 +197,7 @@ scmi_base_implementation_list_get(const struct scmi_protocol_handle *ph,
                        break;
 
                loop_num_ret = le32_to_cpu(*num_ret);
-               if (tot_num_ret + loop_num_ret > MAX_PROTOCOLS_IMP) {
+               if (loop_num_ret > MAX_PROTOCOLS_IMP - tot_num_ret) {
                        dev_err(dev, "No. of Protocol > MAX_PROTOCOLS_IMP");
                        break;
                }