hwrng: virtio - ensure reads happen after successful probe

The hwrng core asks for random data in the hwrng_register() call itself
from commit d9e7972619.  This doesn't play well with virtio -- the
DRIVER_OK bit is only set by virtio core on a successful probe, and
we're not yet out of our probe routine when this call is made.  This
causes the host to not acknowledge any requests we put in the virtqueue,
and the insmod or kernel boot process just waits for data to arrive from
the host, which never happens.

CC: Kees Cook <keescook@chromium.org>
CC: Jason Cooper <jason@lakedaemon.net>
CC: Herbert Xu <herbert@gondor.apana.org.au>
CC: <stable@vger.kernel.org> # For v3.15+
Reviewed-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index f3e71501de54..e9b15bc18b4d 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -38,6 +38,8 @@ struct virtrng_info {
 	int index;
 };
 
+static bool probe_done;
+
 static void random_recv_done(struct virtqueue *vq)
 {
 	struct virtrng_info *vi = vq->vdev->priv;
@@ -67,6 +69,13 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
 	int ret;
 	struct virtrng_info *vi = (struct virtrng_info *)rng->priv;
 
+	/*
+	 * Don't ask host for data till we're setup.  This call can
+	 * happen during hwrng_register(), after commit d9e7972619.
+	 */
+	if (unlikely(!probe_done))
+		return 0;
+
 	if (!vi->busy) {
 		vi->busy = true;
 		init_completion(&vi->have_data);
@@ -137,6 +146,7 @@ static int probe_common(struct virtio_device *vdev)
 		return err;
 	}
 
+	probe_done = true;
 	return 0;
 }