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

[Haiyang Zhang <haiyangz@microsoft.com>]

> -----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
> <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>;
> Michael Kelley <mikelley@microsoft.com>; Andrea Parri (Microsoft)
> <parri.andrea@gmail.com>; Dexuan Cui <decui@microsoft.com>
> 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
>  				 * 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>