hv_utils: Add validation for untrusted Hyper-V values

For additional robustness in the face of Hyper-V errors or malicious
behavior, validate all values that originate from packets that Hyper-V
has sent to the guest in the host-to-guest ring buffer. Ensure that
invalid values cannot cause indexing off the end of the icversion_data
array in vmbus_prep_negotiate_resp().

Signed-off-by: Andres Beltran <lkmlabelt@gmail.com>
Co-developed-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by:  Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20201109100704.9152-1-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

1 files changed, 52 insertions, 37 deletions

diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
index 783779e4cc1a..2267bd4c3472 100644
--- a/drivers/hv/hv_snapshot.c
+++ b/drivers/hv/hv_snapshot.c
@@ -298,49 +298,64 @@ void hv_vss_onchannelcallback(void *context)
 	if (vss_transaction.state > HVUTIL_READY)
 		return;
 
-	vmbus_recvpacket(channel, recv_buffer, HV_HYP_PAGE_SIZE * 2, &recvlen,
-			 &requestid);
-
-	if (recvlen > 0) {
-		icmsghdrp = (struct icmsg_hdr *)&recv_buffer[
-			sizeof(struct vmbuspipe_hdr)];
-
-		if (icmsghdrp->icmsgtype == ICMSGTYPE_NEGOTIATE) {
-			if (vmbus_prep_negotiate_resp(icmsghdrp,
-				 recv_buffer, fw_versions, FW_VER_COUNT,
-				 vss_versions, VSS_VER_COUNT,
-				 NULL, &vss_srv_version)) {
-
-				pr_info("VSS IC version %d.%d\n",
-					vss_srv_version >> 16,
-					vss_srv_version & 0xFFFF);
-			}
-		} else {
-			vss_msg = (struct hv_vss_msg *)&recv_buffer[
-				sizeof(struct vmbuspipe_hdr) +
-				sizeof(struct icmsg_hdr)];
-
-			/*
-			 * Stash away this global state for completing the
-			 * transaction; note transactions are serialized.
-			 */
-
-			vss_transaction.recv_len = recvlen;
-			vss_transaction.recv_req_id = requestid;
-			vss_transaction.msg = (struct hv_vss_msg *)vss_msg;
-
-			schedule_work(&vss_handle_request_work);
+	if (vmbus_recvpacket(channel, recv_buffer, HV_HYP_PAGE_SIZE * 2, &recvlen, &requestid)) {
+		pr_err_ratelimited("VSS request received. Could not read into recv buf\n");
+		return;
+	}
+
+	if (!recvlen)
+		return;
+
+	/* Ensure recvlen is big enough to read header data */
+	if (recvlen < ICMSG_HDR) {
+		pr_err_ratelimited("VSS request received. Packet length too small: %d\n",
+				   recvlen);
+		return;
+	}
+
+	icmsghdrp = (struct icmsg_hdr *)&recv_buffer[sizeof(struct vmbuspipe_hdr)];
+
+	if (icmsghdrp->icmsgtype == ICMSGTYPE_NEGOTIATE) {
+		if (vmbus_prep_negotiate_resp(icmsghdrp,
+				recv_buffer, recvlen,
+				fw_versions, FW_VER_COUNT,
+				vss_versions, VSS_VER_COUNT,
+				NULL, &vss_srv_version)) {
+
+			pr_info("VSS IC version %d.%d\n",
+				vss_srv_version >> 16,
+				vss_srv_version & 0xFFFF);
+		}
+	} else if (icmsghdrp->icmsgtype == ICMSGTYPE_VSS) {
+		/* Ensure recvlen is big enough to contain hv_vss_msg */
+		if (recvlen < ICMSG_HDR + sizeof(struct hv_vss_msg)) {
+			pr_err_ratelimited("Invalid VSS msg. Packet length too small: %u\n",
+					   recvlen);
 			return;
 		}
+		vss_msg = (struct hv_vss_msg *)&recv_buffer[ICMSG_HDR];
+
+		/*
+		 * Stash away this global state for completing the
+		 * transaction; note transactions are serialized.
+		 */
 
-		icmsghdrp->icflags = ICMSGHDRFLAG_TRANSACTION
-			| ICMSGHDRFLAG_RESPONSE;
+		vss_transaction.recv_len = recvlen;
+		vss_transaction.recv_req_id = requestid;
+		vss_transaction.msg = (struct hv_vss_msg *)vss_msg;
 
-		vmbus_sendpacket(channel, recv_buffer,
-				       recvlen, requestid,
-				       VM_PKT_DATA_INBAND, 0);
+		schedule_work(&vss_handle_request_work);
+		return;
+	} else {
+		pr_err_ratelimited("VSS request received. Invalid msg type: %d\n",
+				   icmsghdrp->icmsgtype);
+		return;
 	}
 
+	icmsghdrp->icflags = ICMSGHDRFLAG_TRANSACTION |
+		ICMSGHDRFLAG_RESPONSE;
+	vmbus_sendpacket(channel, recv_buffer, recvlen, requestid,
+			 VM_PKT_DATA_INBAND, 0);
 }
 
 static void vss_on_reset(void)