qseecom: Validate the incoming length from user space

Check if there is no integer overflow before using req_len and
resp_len (received from user space). If an overflow is detected
then exit the operation.

Change-Id: I0459a6992bb3b280db42be63a275c55fa6105b1c
Signed-off-by: Hariprasad Dhalinarasimha <hnamgund@codeaurora.org>
diff --git a/drivers/misc/qseecom.c b/drivers/misc/qseecom.c
index ac67c9d..d1fc8e4 100644
--- a/drivers/misc/qseecom.c
+++ b/drivers/misc/qseecom.c
@@ -1014,6 +1014,11 @@
 		return -EINVAL;
 	}
 
+	if (req->cmd_req_len > UINT_MAX - req->resp_len) {
+		pr_err("Integer overflow detected in req_len & rsp_len, exiting now\n");
+		return -EINVAL;
+	}
+
 	reqd_len_sb_in = req->cmd_req_len + req->resp_len;
 	if (reqd_len_sb_in > data->client.sb_length) {
 		pr_debug("Not enough memory to fit cmd_buf and "