linux-kernel - [PATCH 03/22] firmware: arm_scmi: Fix Base list protocols enumeration

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Date:   Wed, 30 Mar 2022 16:05:32 +0100
From:   Cristian Marussi <cristian.marussi@....com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     sudeep.holla@....com, james.quinlan@...adcom.com,
        Jonathan.Cameron@...wei.com, f.fainelli@...il.com,
        etienne.carriere@...aro.org, vincent.guittot@...aro.org,
        souvik.chakravarty@....com, cristian.marussi@....com
Subject: [PATCH 03/22] firmware: arm_scmi: Fix Base list protocols enumeration

While enumerating protocols implemented by the SCMI backend server 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.

Fixes: b6f20ff8bd9 ("firmware: arm_scmi: add common infrastructure and support for base protocol")
Signed-off-by: Cristian Marussi <cristian.marussi@....com>
---
 drivers/firmware/arm_scmi/base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/arm_scmi/base.c b/drivers/firmware/arm_scmi/base.c
index ebaef5d320af..f279146f8110 100644
--- 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;
 		}
-- 
2.32.0