On Wed, Feb 24, 2021 at 07:50:09AM -0500, Sasha Levin wrote:
> From: "Andrea Parri (Microsoft)" <parri.and...@gmail.com>
>
> [ Upstream commit e4d221b42354b2e2ddb9187a806afb651eee2cda ]
>
> 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 <juv...@microsoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.and...@gmail.com>
> Reviewed-by: Michael Kelley <mikel...@microsoft.com>
> Link: https://lore.kernel.org/r/20201209070827.29335-6-parri.and...@gmail.com
> Signed-off-by: Wei Liu <wei....@kernel.org>
> Signed-off-by: Sasha Levin <sas...@kernel.org>
Sasha - This patch is one of a group of patches where a Linux guest running on
Hyper-V will start assuming that hypervisor behavior might be malicious, and
guards against such behavior. Because this is a new assumption, these patches
are more properly treated as new functionality rather than as bug fixes. So I
would propose that we *not* bring such patches back to stable branches.
Thanks,
Andrea
> ---
> 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 1d44bb635bb84..a9f58840f85dc 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -1049,6 +1049,18 @@ 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 5ddb479c4d4cb..ef3573e99d989 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -803,6 +803,7 @@ 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;
> --
> 2.27.0
>
