random: fix soft lockup when trying to read from an uninitialized blocking pool

Fixes: eb9d1bf0: "random: only read from /dev/random after its pool has received 128 bits"
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

drivers/char/random.c

@@ -772,8 +772,11 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
 	if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
 		goto retry;
 
-	if (has_initialized)
+	if (has_initialized) {
 		r->initialized = 1;
+		wake_up_interruptible(&random_read_wait);
+		kill_fasync(&fasync, SIGIO, POLL_IN);
+	}
 
 	trace_credit_entropy_bits(r->name, nbits,
 				  entropy_count >> ENTROPY_SHIFT, _RET_IP_);
@@ -789,6 +792,13 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
 			entropy_bits = r->entropy_count >> ENTROPY_SHIFT;
 		}
 
+		/* initialize the blocking pool if necessary */
+		if (entropy_bits >= random_read_wakeup_bits &&
+		    !other->initialized) {
+			schedule_work(&other->push_work);
+			return;
+		}
+
 		/* should we wake readers? */
 		if (entropy_bits >= random_read_wakeup_bits &&
 		    wq_has_sleeper(&random_read_wait)) {
@@ -1936,8 +1946,8 @@ _random_read(int nonblock, char __user *buf, size_t nbytes)
 			return -EAGAIN;
 
 		wait_event_interruptible(random_read_wait,
-			ENTROPY_BITS(&input_pool) >=
-			random_read_wakeup_bits);
+		    blocking_pool.initialized &&
+		    (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits));
 		if (signal_pending(current))
 			return -ERESTARTSYS;
 	}