virtio: handle short buffers in virtio_rng.

If the device fills less than 4 bytes of our random buffer, we'll
BUG_ON.  It's nicer to handle the case where it partially fills the
buffer (the protocol doesn't explicitly bad that).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index f2041fe..32216b6 100644 (file)
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -35,13 +35,13 @@ static DECLARE_COMPLETION(have_data);
 
 static void random_recv_done(struct virtqueue *vq)
 {
-       int len;
+       unsigned int len;
 
        /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
        if (!vq->vq_ops->get_buf(vq, &len))
                return;
 
-       data_left = len / sizeof(random_data[0]);
+       data_left += len;
        complete(&have_data);
 }
 
@@ -49,7 +49,7 @@ static void register_buffer(void)
 {
        struct scatterlist sg;
 
-       sg_init_one(&sg, random_data, RANDOM_DATA_SIZE);
+       sg_init_one(&sg, random_data+data_left, RANDOM_DATA_SIZE-data_left);
        /* There should always be room for one buffer. */
        if (vq->vq_ops->add_buf(vq, &sg, 0, 1, random_data) != 0)
                BUG();
@@ -59,24 +59,32 @@ static void register_buffer(void)
 /* At least we don't udelay() in a loop like some other drivers. */
 static int virtio_data_present(struct hwrng *rng, int wait)
 {
-       if (data_left)
+       if (data_left >= sizeof(u32))
                return 1;
 
+again:
        if (!wait)
                return 0;
 
        wait_for_completion(&have_data);
+
+       /* Not enough?  Re-register. */
+       if (unlikely(data_left < sizeof(u32))) {
+               register_buffer();
+               goto again;
+       }
+
        return 1;
 }
 
 /* virtio_data_present() must have succeeded before this is called. */
 static int virtio_data_read(struct hwrng *rng, u32 *data)
 {
-       BUG_ON(!data_left);
-
-       *data = random_data[--data_left];
+       BUG_ON(data_left < sizeof(u32));
+       data_left -= sizeof(u32);
+       *data = random_data[data_left / 4];
 
-       if (!data_left) {
+       if (data_left < sizeof(u32)) {
                init_completion(&have_data);
                register_buffer();
        }