3 files changed, 63 insertions, 11 deletions

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 334601cc81cf..c4419ea1ab07 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -55,16 +55,41 @@ static DEFINE_MUTEX(rng_mutex);
 static int data_avail;
 static u8 *rng_buffer;
 
+static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
+                               int wait);
+
 static size_t rng_buffer_size(void)
 {
         return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
 }
 
+static void add_early_randomness(struct hwrng *rng)
+{
+        unsigned char bytes[16];
+        int bytes_read;
+
+        /*
+         * Currently only virtio-rng cannot return data during device
+         * probe, and that's handled in virtio-rng.c itself.  If there
+         * are more such devices, this call to rng_get_data can be
+         * made conditional here instead of doing it per-device.
+         */
+        bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
+        if (bytes_read > 0)
+                add_device_randomness(bytes, bytes_read);
+}
+
 static inline int hwrng_init(struct hwrng *rng)
 {
-        if (!rng->init)
-                return 0;
-        return rng->init(rng);
+        if (rng->init) {
+                int ret;
+
+                ret =  rng->init(rng);
+                if (ret)
+                        return ret;
+        }
+        add_early_randomness(rng);
+        return 0;
 }
 
 static inline void hwrng_cleanup(struct hwrng *rng)
@@ -304,8 +329,6 @@ int hwrng_register(struct hwrng *rng)
 {
         int err = -EINVAL;
         struct hwrng *old_rng, *tmp;
-        unsigned char bytes[16];
-        int bytes_read;
 
         if (rng->name == NULL ||
             (rng->data_read == NULL && rng->read == NULL))
@@ -347,9 +370,17 @@ int hwrng_register(struct hwrng *rng)
         INIT_LIST_HEAD(&rng->list);
         list_add_tail(&rng->list, &rng_list);
 
-        bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
-        if (bytes_read > 0)
-                add_device_randomness(bytes, bytes_read);
+        if (old_rng && !rng->init) {
+                /*
+                 * Use a new device's input to add some randomness to
+                 * the system.  If this rng device isn't going to be
+                 * used right away, its init function hasn't been
+                 * called yet; so only use the randomness from devices
+                 * that don't need an init callback.
+                 */
+                add_early_randomness(rng);
+        }
+
 out_unlock:
         mutex_unlock(&rng_mutex);
 out:
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;
 }
 
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0a7ac0a7b252..71529e196b84 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -641,7 +641,7 @@ retry:
                 } while (unlikely(entropy_count < pool_size-2 && pnfrac));
         }
 
-        if (entropy_count < 0) {
+        if (unlikely(entropy_count < 0)) {
                 pr_warn("random: negative entropy/overflow: pool %s count %d\n",
                         r->name, entropy_count);
                 WARN_ON(1);
@@ -981,7 +981,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
                       int reserved)
 {
         int entropy_count, orig;
-        size_t ibytes;
+        size_t ibytes, nfrac;
 
         BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
 
@@ -999,7 +999,17 @@ retry:
         }
         if (ibytes < min)
                 ibytes = 0;
-        if ((entropy_count -= ibytes << (ENTROPY_SHIFT + 3)) < 0)
+
+        if (unlikely(entropy_count < 0)) {
+                pr_warn("random: negative entropy count: pool %s count %d\n",
+                        r->name, entropy_count);
+                WARN_ON(1);
+                entropy_count = 0;
+        }
+        nfrac = ibytes << (ENTROPY_SHIFT + 3);
+        if ((size_t) entropy_count > nfrac)
+                entropy_count -= nfrac;
+        else
                 entropy_count = 0;
 
         if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
@@ -1376,6 +1386,7 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
                             "with %d bits of entropy available\n",
                             current->comm, nonblocking_pool.entropy_total);
 
+        nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3));
         ret = extract_entropy_user(&nonblocking_pool, buf, nbytes);
 
         trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool),