Restricting reprogramming of a redirected USB device
View Patent ↗Reprogramming of a redirected USB device can be restricted to prevent the redirected USB device's firmware from being modified maliciously. A virtual bus driver can be configured to monitor USB request blocks (URBs) to identify whether an URB pertains to an attempt to alter the firmware of a redirected USB device. When an URB is identified as pertaining to an attempt to alter the firmware, the virtual bus driver can block the URB unless the URB is associated with an authorized user or application. In this way, only an authorized user or application will be allowed to modify the firmware of a redirected USB device thereby ensuring that a malicious user or application cannot modify the firmware in an improper manner.
1. A method, performed by a virtual bus driver that is loaded on a server in a virtual desktop infrastructure (VDI) environment, for selectively blocking a USB request block (URB) to prevent a redirected USB device's firmware from being improperly modified, the method comprising:
receiving an URB at the virtual bus driver, the URB being directed to a USB device that is being redirected by a client terminal within the VDI environment;
accessing, by the virtual bus driver, a header of the URB to determine whether a function member defined within the header is set to a code that specifies that the URB defines a vendor specific command to be performed by the USB device; and
when the virtual bus driver determines that the function member defined within the header is set to the code that specifies that the URB defines a vendor specific command, blocking, by the virtual bus driver, the URB.
2. The method of claim 1 , wherein the code that specifies that the URB defines a vendor specific command is URB_FUNCTION_VENDOR_DEVICE.
3. The method of claim 1 , wherein blocking the URB includes returning an error to a higher level driver.
4. The method of claim 1 , further comprising:
when the virtual bus driver determines that the function member defined within the header is set to the code that specifies that the URB defines a vendor specific command and that the URB is associated with an authorized application or user, forwarding, by the virtual bus driver, the URB to an agent such that the URB will be routed to the USB device.
5. The method of claim 4 , wherein determining that the URB is associated with an authorized application or user comprises identifying a process ID associated with an I/O request packet (IRP) for which the URB was generated.
6. The method of claim 1 , wherein, when the virtual bus driver determines that the function member defined within the header is not set to the code that specifies that the URB defines a vendor specific command, the method further comprises:
determining, by the virtual bus driver, whether the URB pertains to a bulk transfer;
when the virtual bus driver determines that the URB pertains to a bulk transfer, determining, by the virtual bus driver, whether the URB specifies a SCSI vendor opcode; and
when the virtual bus driver determines that the URB specifies a SCSI vendor opcode, blocking, by the virtual bus driver, the URB.
7. The method of claim 6 , further comprising:
when the virtual bus driver determines that the URB specifies a SCSI vendor opcode and that the URB is associated with an authorized application or user, forwarding, by the virtual bus driver, the URB to an agent such that the URB will be routed to the USB device.
8. The method of claim 6 , wherein determining whether the URB pertains to a bulk transfer comprises determining whether the URB includes the URB_BULK_OR_INTERRUPT_TRANSFER structure.
9. The method of claim 8 , wherein determining whether the URB specifies a SCSI vendor opcode comprises determining whether the URB_BULK_OR_INTERRUPT_TRANSFER structure defines a command block wrapper that includes a command block containing a SCSI vendor opcode.
10. The method of claim 6 , wherein the SCSI vendor opcode comprises one of 0x06, 0xC6, or 0xC7.
11. The method of claim 6 , further comprising:
when the virtual bus driver determines that the URB does not pertain to a bulk transfer, forwarding, by the virtual bus driver, the URB to an agent such that the URB will be routed to the USB device.
12. The method of claim 6 , further comprising:
when the virtual bus driver determines that the URB pertains to a bulk transfer but does not specify a SCSI vendor opcode, forwarding, by the virtual bus driver, the URB to an agent such that the URB will be routed to the USB device.
13. One or more computer storage media storing computer executable instructions which when executed by one or more processors implement a virtual bus driver that is configured to execute on a server in a virtual desktop infrastructure (VDI) environment, the virtual bus driver being configured to selectively block USB request blocks (URBs) based on whether the URBs pertain to an attempt to modify firmware of a redirected USB device, the virtual bus driver performing the selective blocking on each received URB by:
determining whether the URB includes a header having a function member set to a code that specifies that the URB defines a vendor specific command, and if so, blocking the URB; and
determining whether the URB pertains to a bulk transfer and defines a command block wrapper having a command block specifying a vendor specific opcode, and if so, blocking the URB.
14. The computer storage media of claim 13 , wherein the virtual bus driver is further configured to:
determine whether an URB to be blocked is associated with an authorized application and/or user, and if so, allowing the URB such that the URB is forwarded towards a target USB device.
15. The computer storage media of claim 13 , wherein determining whether the URB includes a header having a function member set to a code that specifies that the URB defines a vendor specific command comprises determining whether the function member is set to URB_FUNCTION_VENDOR_DEVICE.
16. The computer storage media of claim 13 , wherein determining whether the URB pertains to a bulk transfer comprises determining whether the URB includes the URB_BULK_OR_INTERRUPT_TRANSFER structure.
17. The computer storage media of claim 16 , wherein determining whether the URB defines a command block wrapper having a command block specifying a vendor specific opcode comprises determining whether the URB_BULK_OR_INTERRUPT_TRANSFER structure includes a member that identifies a buffer containing a command block wrapper.
18. The computer storage media of claim 17 , wherein the vendor specific opcode comprises one of 0x06, 0xC6, or 0xC7.
19. One or more computer storage media storing computer executable instructions which when executed implement components of a virtual desktop infrastructure (VDI) environment, the components comprising:
an agent that executes on a server and that is configured to establish remote sessions with client terminals including to implement USB device redirection over the remote sessions; and
a virtual bus driver that executes on the server and that is configured to evaluate each USB request block (URB) that targets a redirected USB device to determine whether the URB pertains to an attempt to modify firmware on the target USB device such that, when the virtual bus driver determines that the URB pertains to an attempt to modify firmware on the target USB device, the URB is routed to the agent only if an application or user associated with the URB is authorized to modify the firmware, wherein the virtual bus driver determines that the URB pertains to an attempt to modify firmware on the target USB device by one of:
determining that a header of the URB includes a function member having a value of URB_FUNCTION_VENDOR_DEVICE; or
determining that the URB pertains to a bulk transfer and defines a command block wrapper having a command block specifying a vendor specific opcode.
20. The computer storage media of claim 19 , wherein the vendor specific opcode comprises one of 0x06, 0xC6, or 0xC7.