[PATCH AUTOSEL 4.14 15/16] Drivers: hv: vmbus: Resolve race condition in vmbus_onoffer_rescind()

Sasha Levin
2021-02-24T14:26:07Z

From: "Andrea Parri (Microsoft)" <parri.andrea@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 <juvazq@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20201209070827.29335-6-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 5bf633c15cd4b..6ddda97030628 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -942,6 +942,18 @@ 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 63cd81e5610d1..22e2c2d75361e 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -710,6 +710,7 @@ 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