Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>,
        Juan Vazquez <juvazq@microsoft.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Sasha Levin <sashal@kernel.org>,
        linux-hyperv@vger.kernel.org
Subject: [PATCH AUTOSEL 4.19 21/26] Drivers: hv: vmbus: Resolve race condition in vmbus_onoffer_rescind()
Date:   Wed, 24 Feb 2021 07:54:29 -0500
Message-Id: <20210224125435.483539-21-sashal@kernel.org>
In-Reply-To: <20210224125435.483539-1-sashal@kernel.org>
References: <20210224125435.483539-1-sashal@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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 7920b0d7e35a7..1322e799938af 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -954,6 +954,18 @@ 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 35461d49d3aee..59525fe25abde 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -736,6 +736,7 @@ 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