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    Subject[PATCH 5.11 260/775] Drivers: hv: vmbus: Avoid use-after-free in vmbus_onoffer_rescind()
    Date
    From: Andrea Parri (Microsoft) <parri.andrea@gmail.com>

    [ Upstream commit e3fa4b747f085d2cda09bba0533b86fa76038635 ]

    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@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/20201209070827.29335-5-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 | 3 +--
    1 file changed, 1 insertion(+), 2 deletions(-)

    diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
    index 1d44bb635bb84..6be9f56cb6270 100644
    --- a/drivers/hv/channel_mgmt.c
    +++ b/drivers/hv/channel_mgmt.c
    @@ -1102,8 +1102,7 @@ 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    * Sub-channel is being rescinded.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
    --
    2.27.0


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