linux-kernel - [PATCH 4/6] Drivers: hv: vmbus: Avoid use-after-free in vmbus_onoffer

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Date:   Wed, 18 Nov 2020 15:36:47 +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 4/6] Drivers: hv: vmbus: Avoid use-after-free in vmbus_onoffer_rescind()

When channel->device_obj is non-NULL, vmbus_onoffer_rescind() could
invoke put_device(), that will eventually release the device and free
the channel object (cf. vmbus_device_release()).  However, a pointer
to the object is dereferenced again later to load the primary_channel.
The use-after-free can be avoided by noticing that this load/check is
redundant if device_obk is non-NULL: primary_channel must be NULL if
device_obj is non-NULL, cf. vmbus_add_channel_work().

Reported-by: Juan Vazquez <juvazq@...rosoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@...il.com>
---
 drivers/hv/channel_mgmt.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 5bc5eef5da159..4072fd1f22146 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -1116,8 +1116,7 @@ static void vmbus_onoffer_rescind(struct vmbus_channel_message_header *hdr)
 			vmbus_device_unregister(channel->device_obj);
 			put_device(dev);
 		}
-	}
-	if (channel->primary_channel != NULL) {
+	} else if (channel->primary_channel != NULL) {
 		/*
 		 * Sub-channel is being rescinded. Following is the channel
 		 * close sequence when initiated from the driveri (refer to
-- 
2.25.1