virtio-rng: fixes for device registration/unregistration

There are several fixes in this patch (mostly because it's hard
splitting them up):

 - Revert the name field in struct hwrng back to 'const'. Also, don't
do an extra kmalloc for the name - just wasteful.
 - Deal with allocation failures properly.
 - Use IDA to allocate device number instead of brute forcing one.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 23 insertions, 18 deletions

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 5b25daa7f798..f3e71501de54 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -25,6 +25,7 @@
 #include <linux/virtio_rng.h>
 #include <linux/module.h>
 
+static DEFINE_IDA(rng_index_ida);
 
 struct virtrng_info {
         struct virtio_device *vdev;
@@ -33,6 +34,8 @@ struct virtrng_info {
         unsigned int data_avail;
         struct completion have_data;
         bool busy;
+        char name[25];
+        int index;
 };
 
 static void random_recv_done(struct virtqueue *vq)
@@ -92,41 +95,45 @@ static void virtio_cleanup(struct hwrng *rng)
 
 static int probe_common(struct virtio_device *vdev)
 {
-        int err, i;
+        int err, index;
         struct virtrng_info *vi = NULL;
 
         vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
-        vi->hwrng.name = kmalloc(40, GFP_KERNEL);
+        if (!vi)
+                return -ENOMEM;
+
+        vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL);
+        if (index < 0) {
+                kfree(vi);
+                return index;
+        }
+        sprintf(vi->name, "virtio_rng.%d", index);
         init_completion(&vi->have_data);
 
-        vi->hwrng.read = virtio_read;
-        vi->hwrng.cleanup = virtio_cleanup;
-        vi->hwrng.priv = (unsigned long)vi;
+        vi->hwrng = (struct hwrng) {
+                .read = virtio_read,
+                .cleanup = virtio_cleanup,
+                .priv = (unsigned long)vi,
+                .name = vi->name,
+        };
         vdev->priv = vi;
 
         /* We expect a single virtqueue. */
         vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input");
         if (IS_ERR(vi->vq)) {
                 err = PTR_ERR(vi->vq);
-                kfree(vi->hwrng.name);
                 vi->vq = NULL;
                 kfree(vi);
-                vi = NULL;
+                ida_simple_remove(&rng_index_ida, index);
                 return err;
         }
 
-        i = 0;
-        do {
-                sprintf(vi->hwrng.name, "virtio_rng.%d", i++);
-                err = hwrng_register(&vi->hwrng);
-        } while (err == -EEXIST);
-
+        err = hwrng_register(&vi->hwrng);
         if (err) {
                 vdev->config->del_vqs(vdev);
-                kfree(vi->hwrng.name);
                 vi->vq = NULL;
                 kfree(vi);
-                vi = NULL;
+                ida_simple_remove(&rng_index_ida, index);
                 return err;
         }
 
@@ -140,10 +147,8 @@ static void remove_common(struct virtio_device *vdev)
         vi->busy = false;
         hwrng_unregister(&vi->hwrng);
         vdev->config->del_vqs(vdev);
-        kfree(vi->hwrng.name);
-        vi->vq = NULL;
+        ida_simple_remove(&rng_index_ida, vi->index);
         kfree(vi);
-        vi = NULL;
 }
 
 static int virtrng_probe(struct virtio_device *vdev)