From: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Sent: Tuesday, December 8, 2020 11:08 PM
>
> An erroneous or malicious host could send multiple rescind messages for
> a same channel. In vmbus_onoffer_rescind(), the guest maps the channel
> ID to obtain a pointer to the channel object and it eventually releases
> such object and associated data. The host could time rescind messages
> and lead to an use-after-free. Add a new flag to the channel structure
> to make sure that only one instance of vmbus_onoffer_rescind() can get
> the reference to the channel object.
>
> Reported-by: Juan Vazquez <juvazq@xxxxxxxxxxxxx>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> ---
> drivers/hv/channel_mgmt.c | 12 ++++++++++++
> include/linux/hyperv.h | 1 +
> 2 files changed, 13 insertions(+)
>
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 4072fd1f22146..68950a1e4b638 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -1063,6 +1063,18 @@ static void vmbus_onoffer_rescind(struct
> vmbus_channel_message_header *hdr)
>
> mutex_lock(&vmbus_connection.channel_mutex);
> channel = relid2channel(rescind->child_relid);
> + if (channel != NULL) {
> + /*
> + * Guarantee that no other instance of vmbus_onoffer_rescind()
> + * has got a reference to the channel object. Synchronize on
> + * &vmbus_connection.channel_mutex.
> + */
> + if (channel->rescind_ref) {
> + mutex_unlock(&vmbus_connection.channel_mutex);
> + return;
> + }
> + channel->rescind_ref = true;
> + }
> mutex_unlock(&vmbus_connection.channel_mutex);
>
> if (channel == NULL) {
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 2ea967bc17adf..f0d48a368f131 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -809,6 +809,7 @@ struct vmbus_channel {
> u8 monitor_bit;
>
> bool rescind; /* got rescind msg */
> + bool rescind_ref; /* got rescind msg, got channel reference */
> struct completion rescind_event;
>
> u32 ringbuffer_gpadlhandle;
> --
> 2.25.1
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
