BACKPORT: memshare: Prevent possible integer overflow

Prevent possible integer overflow by sanitizing the alloc request
size coming from the client against allottable amount of memory.

Change-Id: I74cb0f7b0808f20299586969fd5c810d44c3e576
Signed-off-by: Manoj Prabhu B <quic_bmanoj@quicinc.com>
Signed-off-by: Michael Bestas <mkbestas@lineageos.org>

Author: quic-bmanoj

drivers/soc/qcom/memshare/msm_memshare.c

@@ -563,8 +563,12 @@ static int handle_alloc_generic_req(void *req_h, void *req, void *conn_h)
 		return -EINVAL;
 	}
 
-	if (!memblock[client_id].allotted) {
-		if (alloc_req->client_id == 1 && alloc_req->num_bytes > 0)
+	if (!memblock[client_id].allotted && alloc_req->num_bytes > 0) {
+
+		if (alloc_req->num_bytes > memblock[client_id].size)
+			alloc_req->num_bytes = memblock[client_id].size;
+
+		if (alloc_req->client_id == 1)
 			size = alloc_req->num_bytes + MEMSHARE_GUARD_BYTES;
 		else
 			size = alloc_req->num_bytes;