Drivers: hv: Don't reset VMBus connection state on error/exit paths

Overview

In the Linux kernel, the following vulnerability has been resolved:

Drivers: hv: Don't reset VMBus connection state on error/exit paths

In two places, current code forces vmbus_connection.conn_state to DISCONNECTED prior to calling vmbus_disconnect(). But vmbus_disconnect() calls vmbus_initiate_unload(), which unloads the VMBus connection only if the conn_state is CONNECTED. Consequently, the connection remains and the Hyper-V host might continue to send messages or post VMBus interrupts.

The problem was introduced in commit 74347a99e73ae ("x86/Hyper-V: Unload vmbus channel in hv panic callback"), in that vmbus_initiate_unload() started checking the current connection state before doing the unload. This commit removed some occurrences where conn_state was forced to DISCONNECTED, but these two remained, apparently due to an oversight at the time.

Fix this by not forcing conn_state to DISCONNECTED during VMBus exit, or if a failure occurs when establishing the connection in the first place. Whatever value conn_state has at the time is then read by vmbus_initiate_unload() to determine if there is a connection to be unloaded.

Affected

• Linux >= 74347a99e73ae00b8385f1209aaea193c670f901 < f47ce27af80b87cc684d5c12b65506af498ac7e5
• Linux >= 74347a99e73ae00b8385f1209aaea193c670f901 < 3195546a377c2d8d176d837e8baad5ce15d11195
• Linux >= 74347a99e73ae00b8385f1209aaea193c670f901 < ec31dc39e835ccde0930daccece8c492d28282fc
• Linux 5e059fc0f054309036d3f612bc8b0a502ca58545
• Linux 9f38f7b46de0747c1909e8c557aa21715dce20c5
• Linux caeeb3787167c884b955404a7e669fd77f267e44
• Linux >= 4.19.118 < 4.20
• Linux >= 5.4.35 < 5.5
• Linux >= 5.6.7 < 5.7
• Linux 5.7

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.