[PATCH 2/3] firmware: arm_scmi: imx: Validate MISC control response size

[Sudeep Holla <sudeep.holla@kernel.org>]

scmi_imx_misc_ctrl_get() uses @num to report the number of
values returned by firmware, but it did not retain the caller's value
as the capacity of @val.

A response with more values than the caller allocated was copied into
@val unchecked. For example, the MQS regmap callback supplies storage
for one value. Retain the input capacity and reject responses exceeding
it before copying, then update @num only after a successful copy.

Document the in/out @num contract of the exported helper.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/bug/linux-6897b44a-57fb-4964-95f8-447d0ce526e4
Fixes: 61c9f03e22fc ("firmware: arm_scmi: Add initial support for i.MX MISC protocol")
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>
---
 .../firmware/arm_scmi/vendors/imx/imx-sm-misc.c  | 16 ++++++++++++----
 include/linux/firmware/imx/sm.h                  |  6 ++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/firmware/arm_scmi/vendors/imx/imx-sm-misc.c b/drivers/firmware/arm_scmi/vendors/imx/imx-sm-misc.c
index 0c708b2dd496..f00f7acba845 100644
--- a/drivers/firmware/arm_scmi/vendors/imx/imx-sm-misc.c
+++ b/drivers/firmware/arm_scmi/vendors/imx/imx-sm-misc.c
@@ -273,10 +273,16 @@ static int scmi_imx_misc_ctrl_get(const struct scmi_protocol_handle *ph,
 {
 	struct scmi_imx_misc_ctrl_get_out *out;
 	struct scmi_xfer *t;
+	u32 num_values, max_values;
 	int ret, i;
 	int max_msg_size = ph->hops->get_max_msg_size(ph);
 	int max_num = (max_msg_size - sizeof(*out)) / sizeof(__le32);
 
+	if (!num || !val || !*num)
+		return -EINVAL;
+
+	max_values = *num;
+
 	ret = scmi_imx_misc_ctrl_validate_id(ph, ctrl_id);
 	if (ret)
 		return ret;
@@ -290,16 +296,18 @@ static int scmi_imx_misc_ctrl_get(const struct scmi_protocol_handle *ph,
 	ret = ph->xops->do_xfer(ph, t);
 	if (!ret) {
 		out = t->rx.buf;
-		*num = le32_to_cpu(out->num);
+		num_values = le32_to_cpu(out->num);
 
-		if (*num >= max_num ||
-		    *num * sizeof(__le32) > t->rx.len - sizeof(__le32)) {
+		if (num_values > max_values || num_values >= max_num ||
+		    num_values * sizeof(__le32) > t->rx.len - sizeof(__le32)) {
 			ph->xops->xfer_put(ph, t);
 			return -EINVAL;
 		}
 
-		for (i = 0; i < *num; i++)
+		for (i = 0; i < num_values; i++)
 			val[i] = le32_to_cpu(out->val[i]);
+
+		*num = num_values;
 	}
 
 	ph->xops->xfer_put(ph, t);
diff --git a/include/linux/firmware/imx/sm.h b/include/linux/firmware/imx/sm.h
index ba5d93bd6158..0aec7da0ae78 100644
--- a/include/linux/firmware/imx/sm.h
+++ b/include/linux/firmware/imx/sm.h
@@ -29,6 +29,12 @@
 #define SCMI_IMX952_CTRL_BYPASS_AUDMIX	8U      /* WAKE AUDMIX */
 
 #if IS_ENABLED(CONFIG_IMX_SCMI_MISC_DRV)
+/**
+ * scmi_imx_misc_ctrl_get() - Read an i.MX MISC control
+ * @id: Control identifier
+ * @num: On entry, capacity of @val in words; on return, words read
+ * @val: Buffer for the control value
+ */
 int scmi_imx_misc_ctrl_get(u32 id, u32 *num, u32 *val);
 int scmi_imx_misc_ctrl_set(u32 id, u32 val);
 #else
-- 
2.43.0