Add periodic DRBG health checks as required by SP800-90.

diff --git a/fips/fips.h b/fips/fips.h
index f9c3dde..155cbbc 100644
--- a/fips/fips.h
+++ b/fips/fips.h

@@ -244,6 +244,7 @@
 #define FIPS_F_FIPS_CIPHERINIT				 109
 #define FIPS_F_FIPS_DIGESTINIT				 110
 #define FIPS_F_FIPS_DRBG_BYTES				 111
+#define FIPS_F_FIPS_DRBG_CHECK				 146
 #define FIPS_F_FIPS_DRBG_CPRNG_TEST			 112
 #define FIPS_F_FIPS_DRBG_GENERATE			 113
 #define FIPS_F_FIPS_DRBG_HEALTH_CHECK			 114

diff --git a/fips/rand/fips_drbg_lib.c b/fips/rand/fips_drbg_lib.c
index 10d549b..6d983aa 100644
--- a/fips/rand/fips_drbg_lib.c
+++ b/fips/rand/fips_drbg_lib.c

@@ -71,6 +71,9 @@
 	dctx->flags = flags;
 	dctx->type = type;
 
+	dctx->health_check_cnt = 0;
+	dctx->health_check_interval = DRBG_HEALTH_INTERVAL;
+
 	rv = fips_drbg_hash_init(dctx);
 
 	if (rv == -2)
@@ -277,6 +280,24 @@
 	return 0;
 	}
 
+static int fips_drbg_check(DRBG_CTX *dctx)
+	{
+	if (dctx->flags & DRBG_FLAG_TEST)
+		return 1;
+	dctx->health_check_cnt++;
+	if (dctx->health_check_cnt >= dctx->health_check_interval)
+		{
+		DRBG_CTX tctx;
+		if (!fips_drbg_kat(&tctx, dctx->type,
+						dctx->flags | DRBG_FLAG_TEST))
+			{
+			FIPSerr(FIPS_F_FIPS_DRBG_CHECK, FIPS_R_SELFTEST_FAILURE);
+			return 0;
+			}
+		dctx->health_check_cnt = 0;
+		}
+	return 1;
+	}
 
 int FIPS_drbg_generate(DRBG_CTX *dctx, unsigned char *out, size_t outlen,
 			int strength, int prediction_resistance,
@@ -284,6 +305,9 @@
 	{
 	int r = 0;
 
+	if (!fips_drbg_check(dctx))
+		return 0;
+
 	if (dctx->status != DRBG_STATUS_READY
 		&& dctx->status != DRBG_STATUS_RESEED)
 		{
@@ -408,6 +432,11 @@
 	return dctx->strength;
 	}
 
+void FIPS_drbg_set_check_interval(DRBG_CTX *dctx, int interval)
+	{
+	dctx->health_check_interval = interval;
+	}
+
 static int drbg_stick = 0;
 
 void FIPS_drbg_stick(void)

diff --git a/fips/rand/fips_rand.h b/fips/rand/fips_rand.h
index 6186c00..44a3c4f 100644
--- a/fips/rand/fips_rand.h
+++ b/fips/rand/fips_rand.h

@@ -108,6 +108,7 @@
 void FIPS_drbg_set_app_data(DRBG_CTX *ctx, void *app_data);
 size_t FIPS_drbg_get_blocklength(DRBG_CTX *dctx);
 int FIPS_drbg_get_strength(DRBG_CTX *dctx);
+void FIPS_drbg_set_check_interval(DRBG_CTX *dctx, int interval);
 
 DRBG_CTX *FIPS_get_default_drbg(void);
 const RAND_METHOD *FIPS_drbg_method(void);

diff --git a/fips/rand/fips_rand_lcl.h b/fips/rand/fips_rand_lcl.h
index 94f58ea..eeed0ec 100644
--- a/fips/rand/fips_rand_lcl.h
+++ b/fips/rand/fips_rand_lcl.h

@@ -105,6 +105,8 @@
  */
 #define DRBG_MAX_BLOCK			EVP_MAX_MD_SIZE
 
+#define DRBG_HEALTH_INTERVAL		(1 << 24)
+
 /* DRBG context structure */
 
 struct drbg_ctx_st
@@ -114,6 +116,8 @@
 	int type;
 	/* Various flags */
 	unsigned int flags;
+	/* Used for periodic health checks */
+	int health_check_cnt, health_check_interval;
 
 	/* The following parameters are setup by mechanism drbg_init() call */
 	int strength;