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Date:   Tue, 5 Oct 2021 20:14:21 +0200
From:   Andrea Parri <parri.andrea@gmail.com>
To:     Michael Kelley <mikelley@microsoft.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>,
        "James E . J . Bottomley" <jejb@linux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        Dexuan Cui <decui@microsoft.com>
Subject: Re: [PATCH] scsi: storvsc: Fix validation for unsolicited incoming
 packets
Message-ID: <20211005181421.GA1714@anparri>
References: <20211005114103.3411-1-parri.andrea@gmail.com>
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> > @@ -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
> > +
> 
> I know you have determined experimentally that Hyper-V sends
> unsolicited packets with the above length, so the idea is to validate
> that the guest actually gets packets at least that big.  But I wonder if
> we should think about this slightly differently.
> 
> The goal is for the storvsc driver to protect itself against bad or
> malicious messages from Hyper-V.  For the unsolicited messages, the
> only field that this storvsc driver needs to access is the
> vstor_packet->operation field.

Eh, this is one piece of information I was looking for...  ;-)


>So an alternate approach is to set
> the minimum length as small as possible while ensuring that field is valid.

The fact is, I'm not sure how to do it for unsolicited messages.
Current code ensures/checks != COMPLETE_IO.  Your comment above
and code audit suggest that we should add a check != FCHBA_DATA.
I saw ENUMERATE_BUS messages, code only using their "operation".

And, again, this is only based on current code/observations...

So, maybe you mean something like this (on top of this patch)?

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 349c1071a98d4..8fedac3c7597a 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -292,9 +292,6 @@ 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;
@@ -1291,7 +1288,7 @@ static void storvsc_on_channel_callback(void *context)
 		u32 pktlen = hv_pkt_datalen(desc);
 		u64 rqst_id = desc->trans_id;
 		u32 minlen = rqst_id ? sizeof(struct vstor_packet) -
-			stor_device->vmscsi_size_delta : VSTOR_MIN_UNSOL_PKT_SIZE;
+			stor_device->vmscsi_size_delta : sizeof(enum vstor_packet_operation);
 
 		if (pktlen < minlen) {
 			dev_err(&device->device,
@@ -1315,7 +1312,8 @@ static void storvsc_on_channel_callback(void *context)
 				 * storvsc_on_io_completion() with a guest memory address that is
 				 * zero if Hyper-V were to construct and send such a bogus packet.
 				 */
-				if (packet->operation == VSTOR_OPERATION_COMPLETE_IO) {
+				if (packet->operation == VSTOR_OPERATION_COMPLETE_IO ||
+				    packet->operation == VSTOR_OPERATION_FCHBA_DATA) {
 					dev_err(&device->device, "Invalid packet with ID of 0\n");
 					continue;
 				}

Thanks,
  Andrea