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

-----Original Message-----
From: Haiyang Zhang
Sent: Tuesday, September 28, 2021 6:06 PM
To: Andrea Parri (Microsoft) <parri.andrea@gmail.com>; linux-
kernel@vger.kernel.org; linux-hyperv@vger.kernel.org; linux-
scsi@vger.kernel.org
Cc: KY Srinivasan <kys@microsoft.com>; Stephen Hemminger
[off-list ref]; Wei Liu [off-list ref]; James E . J .
Bottomley [off-list ref]; Martin K . Petersen
[off-list ref]; Michael Kelley [off-list ref];
Dexuan Cui [off-list ref]
Subject: RE: [RFC PATCH] scsi: storvsc: Fix validation for unsolicited
incoming packets

quoted

-----Original Message-----
From: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Sent: Tuesday, September 28, 2021 12:38 PM
To: linux-kernel@vger.kernel.org; linux-hyperv@vger.kernel.org; linux-
scsi@vger.kernel.org
Cc: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
[off-list ref]; Stephen Hemminger [off-list ref];
Wei Liu [off-list ref]; James E . J . Bottomley
[off-list ref]; Martin K . Petersen
[off-list ref]; Michael Kelley [off-list ref];
Andrea Parri (Microsoft) [off-list ref]; Dexuan Cui
[off-list ref]
Subject: [RFC PATCH] scsi: storvsc: Fix validation for unsolicited
incoming packets

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

quoted

 				 * from the ring buffer.  If the operation in the

vstor_packet is

The patch looks good. But for readability, I'd suggested put the length
checks together like this:

	u32 minlen = rqst_id ? sizeof(struct vstor_packet) -
		stor_device->vmscsi_size_delta : VSTOR_MIN_UNSOL_PKT_SIZE;

	if (pktlen < minlen) {
		dev_err(&device->device,
			   "Invalid pkt: id=%llu, len=%u, minlen=%u\n",
			   rqst_id, pktlen, minlen);
		continue;
	}

Thanks.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>

The tag was meant to be:
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>

Thanks.