Drivers: hv: check VMBus messages lengths

VMBus message handlers (channel_message_table) receive a pointer to
'struct vmbus_channel_message_header' and cast it to a structure of their
choice, which is sometimes longer than the header. We, however, don't check
that the message is long enough so in case hypervisor screws up we'll be
accessing memory beyond what was allocated for temporary buffer.

Previously, we used to always allocate and copy 256 bytes from message page
to temporary buffer but this is hardly better: in case the message is
shorter than we expect we'll be trying to consume garbage as some real
data and no memory guarding technique will be able to identify an issue.

Introduce 'min_payload_len' to 'struct vmbus_channel_message_table_entry'
and check against it in vmbus_on_msg_dpc(). Note, we can't require the
exact length as new hypervisor versions may add extra fields to messages,
we only check that the message is not shorter than we expect.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20200406104326.45361-1-vkuznets@redhat.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 70b30e223a57..ab560ac9c040 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -317,6 +317,7 @@ struct vmbus_channel_message_table_entry {
 	enum vmbus_channel_message_type message_type;
 	enum vmbus_message_handler_type handler_type;
 	void (*message_handler)(struct vmbus_channel_message_header *msg);
+	u32 min_payload_len;
 };
 
 extern const struct vmbus_channel_message_table_entry