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Message-Id: <20201118143649.108465-6-parri.andrea@gmail.com>
Date: Wed, 18 Nov 2020 15:36:48 +0100
From: "Andrea Parri (Microsoft)" <parri.andrea@...il.com>
To: linux-kernel@...r.kernel.org
Cc: "K . Y . Srinivasan" <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
Wei Liu <wei.liu@...nel.org>, linux-hyperv@...r.kernel.org,
Michael Kelley <mikelley@...rosoft.com>,
Juan Vazquez <juvazq@...rosoft.com>,
Saruhan Karademir <skarade@...rosoft.com>,
"Andrea Parri (Microsoft)" <parri.andrea@...il.com>
Subject: [PATCH 5/6] Drivers: hv: vmbus: Resolve race condition in vmbus_onoffer_rescind()
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@...rosoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@...il.com>
---
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
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