163 <freedomsky1986@xxxxxxx> writes: > On 4/1/2020 6:36 PM, Vitaly Kuznetsov wrote: >> Hyper-V Interrupt Message Page (SIMP) has 16 256-byte slots for >> messages. Each message comes with a header (16 bytes) which specifies the >> payload length (up to 240 bytes). vmbus_on_msg_dpc(), however, doesn't >> look at the real message length and copies the whole slot to a temporary >> buffer before passing it to message handlers. This is potentially dangerous >> as hypervisor doesn't have to clean the whole slot when putting a new >> message there and a message handler can get access to some data which >> belongs to a previous message. >> >> Note, this is not currently a problem because all message handlers are >> in-kernel but eventually we may e.g. get this exported to userspace. >> >> Note also, that this is not a performance critical path: messages (unlike >> events) represent rare events so it doesn't really matter (from performance >> point of view) if we copy too much. >> >> Fix the issue by taking into account the real message length. The temporary >> buffer allocated by vmbus_on_msg_dpc() remains fixed size for now. >> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> >> --- >> drivers/hv/vmbus_drv.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c >> index 029378c27421..2b5572146358 100644 >> --- a/drivers/hv/vmbus_drv.c >> +++ b/drivers/hv/vmbus_drv.c >> @@ -1043,7 +1043,8 @@ void vmbus_on_msg_dpc(unsigned long data) >> return; >> >> INIT_WORK(&ctx->work, vmbus_onmessage_work); >> - memcpy(&ctx->msg, msg, sizeof(*msg)); >> + memcpy(&ctx->msg, msg, sizeof(msg->header) + >> + msg->header.payload_size); >> > > Hi Vitaly: > I think we still need to check whether the payload_size passed from > Hyper-V is valid or not here to avoid cross-border issue before doing > copying. Sure, the header.payload_size must be 0 <= header.payload_size <= 240 I'll add the check. -- Vitaly
