[RFC PATCH] scsi: storvsc: Fix validation for unsolicited incoming packets

["Andrea Parri (Microsoft)" <parri.andrea@gmail.com>]

The validation on the length of incoming packets performed in
storvsc_on_channel_callback() does not apply to "unsolicited"
packets with ID of 0 sent by Hyper-V.  Adjust the validation
by handling such unsolicited packets separately.

Fixes: 91b1b640b834b2 ("scsi: storvsc: Validate length of incoming packet in storvsc_on_channel_callback()")
Reported-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
---
The (new) bound, VSTOR_MIN_UNSOL_PKT_SIZE, was "empirically
derived" based on testing and code auditing.  This explains
the RFC tag...

 drivers/scsi/storvsc_drv.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index ebbbc1299c625..a9bbcbbfb54ee 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -292,6 +292,9 @@ struct vmstorage_protocol_version {
 #define STORAGE_CHANNEL_REMOVABLE_FLAG		0x1
 #define STORAGE_CHANNEL_EMULATED_IDE_FLAG	0x2
 
+/* Lower bound on the size of unsolicited packets with ID of 0 */
+#define VSTOR_MIN_UNSOL_PKT_SIZE		48
+
 struct vstor_packet {
 	/* Requested operation type */
 	enum vstor_packet_operation operation;
@@ -1285,11 +1288,13 @@ static void storvsc_on_channel_callback(void *context)
 	foreach_vmbus_pkt(desc, channel) {
 		struct vstor_packet *packet = hv_pkt_data(desc);
 		struct storvsc_cmd_request *request = NULL;
+		u32 pktlen = hv_pkt_datalen(desc);
 		u64 rqst_id = desc->trans_id;
 
-		if (hv_pkt_datalen(desc) < sizeof(struct vstor_packet) -
+		/* Unsolicited packets with ID of 0 are validated separately below */
+		if (rqst_id != 0 && pktlen < sizeof(struct vstor_packet) -
 				stor_device->vmscsi_size_delta) {
-			dev_err(&device->device, "Invalid packet len\n");
+			dev_err(&device->device, "Invalid packet: length=%u\n", pktlen);
 			continue;
 		}
 
@@ -1298,8 +1303,14 @@ static void storvsc_on_channel_callback(void *context)
 		} else if (rqst_id == VMBUS_RQST_RESET) {
 			request = &stor_device->reset_request;
 		} else {
-			/* Hyper-V can send an unsolicited message with ID of 0 */
 			if (rqst_id == 0) {
+				if (pktlen < VSTOR_MIN_UNSOL_PKT_SIZE) {
+					dev_err(&device->device,
+						"Invalid packet with ID of 0: length=%u\n",
+						pktlen);
+					continue;
+				}
+
 				/*
 				 * storvsc_on_receive() looks at the vstor_packet in the message
 				 * from the ring buffer.  If the operation in the vstor_packet is
-- 
2.25.1