[PATCH v3 4/6] Drivers: hv: vmbus: Avoid use-after-free in vmbus_onoffer_rescind()

From: Andrea Parri (Microsoft)
Date: Wed Dec 09 2020 - 02:10:36 EST


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_obj is non-NULL: primary_channel must be NULL if
device_obj is non-NULL, cf. vmbus_add_channel_work().

Fixes: 54a66265d6754b ("Drivers: hv: vmbus: Fix rescind handling")
Reported-by: Juan Vazquez <juvazq@xxxxxxxxxxxxx>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
---
Changes since v2:
- Add Reviewed-by: tag

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* Sub-channel is being rescinded.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