Don't feed OS RNG output into the OS RNG

krb5_c_random_os_entropy() now must be provided by PRNG modules.

ticket: 8499

4 files changed, 40 insertions, 55 deletions

diff --git a/src/lib/crypto/krb/crypto_int.h b/src/lib/crypto/krb/crypto_int.h
index e97c3cd..0f2e472 100644
--- a/src/lib/crypto/krb/crypto_int.h
+++ b/src/lib/crypto/krb/crypto_int.h
@@ -510,6 +510,7 @@ void krb5int_crypto_impl_cleanup(void);
  * PRNG modules must implement the following APIs from krb5.h:
  *   krb5_c_random_add_entropy
  *   krb5_c_random_make_octets
+ *   krb5_c_random_os_entropy
  *
  * PRNG modules should implement these functions.  They are called from the
  * crypto library init and cleanup functions, and can be used to setup and tear
@@ -519,7 +520,7 @@ int k5_prng_init(void);
 void k5_prng_cleanup(void);
 
 /* Used by PRNG modules to gather OS entropy.  Returns true on success. */
-krb5_boolean k5_get_os_entropy(unsigned char *buf, size_t len);
+krb5_boolean k5_get_os_entropy(unsigned char *buf, size_t len, int strong);
 
 /*** Inline helper functions ***/
 
diff --git a/src/lib/crypto/krb/prng.c b/src/lib/crypto/krb/prng.c
index e478b19..9ad24c1 100644
--- a/src/lib/crypto/krb/prng.c
+++ b/src/lib/crypto/krb/prng.c
@@ -36,11 +36,13 @@ krb5_c_random_seed(krb5_context context, krb5_data *data)
 #if defined(_WIN32)
 
 krb5_boolean
-k5_get_os_entropy(unsigned char *buf, size_t len)
+k5_get_os_entropy(unsigned char *buf, size_t len, int strong)
 {
     krb5_boolean result;
     HCRYPTPROV provider;
 
+    /* CryptGenRandom is always considered strong. */
+
     if (!CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
                              CRYPT_VERIFYCONTEXT))
         return FALSE;
@@ -49,22 +51,6 @@ k5_get_os_entropy(unsigned char *buf, size_t len)
     return result;
 }
 
-krb5_error_code KRB5_CALLCONV
-krb5_c_random_os_entropy(krb5_context context, int strong, int *success)
-{
-    int oursuccess = 0;
-    char buf[1024];
-    krb5_data data = make_data(buf, sizeof(buf));
-
-    if (k5_get_os_entropy(buf, sizeof(buf)) &&
-        krb5_c_random_add_entropy(context, KRB5_C_RANDSOURCE_OSRAND,
-                                  &data) == 0)
-        oursuccess = 1;
-    if (success != NULL)
-        *success = oursuccess;
-    return 0;
-}
-
 #else /* not Windows */
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
@@ -107,44 +93,12 @@ cleanup:
 }
 
 krb5_boolean
-k5_get_os_entropy(unsigned char *buf, size_t len)
+k5_get_os_entropy(unsigned char *buf, size_t len, int strong)
 {
-    return read_entropy_from_device("/dev/urandom", buf, len);
-}
+    const char *device;
 
-/* Read entropy from device and contribute it to the PRNG.  Returns true on
- * success. */
-static krb5_boolean
-add_entropy_from_device(krb5_context context, const char *device)
-{
-    krb5_data data;
-    unsigned char buf[64];
-
-    if (!read_entropy_from_device(device, buf, sizeof(buf)))
-        return FALSE;
-    data = make_data(buf, sizeof(buf));
-    return (krb5_c_random_add_entropy(context, KRB5_C_RANDSOURCE_OSRAND,
-                                      &data) == 0);
-}
-
-krb5_error_code KRB5_CALLCONV
-krb5_c_random_os_entropy(krb5_context context, int strong, int *success)
-{
-    int unused;
-    int *oursuccess = (success != NULL) ? success : &unused;
-
-    *oursuccess = 0;
-    /* If we are getting strong data then try that first.  We are
-       guaranteed to cause a reseed of some kind if strong is true and
-       we have both /dev/random and /dev/urandom.  We want the strong
-       data included in the reseed so we get it first.*/
-    if (strong) {
-        if (add_entropy_from_device(context, "/dev/random"))
-            *oursuccess = 1;
-    }
-    if (add_entropy_from_device(context, "/dev/urandom"))
-        *oursuccess = 1;
-    return 0;
+    device = strong ? "/dev/random" : "/dev/urandom";
+    return read_entropy_from_device(device, buf, len);
 }
 
 #endif /* not Windows */
diff --git a/src/lib/crypto/krb/prng_fortuna.c b/src/lib/crypto/krb/prng_fortuna.c
index e70ffa3..017a119 100644
--- a/src/lib/crypto/krb/prng_fortuna.c
+++ b/src/lib/crypto/krb/prng_fortuna.c
@@ -366,7 +366,7 @@ k5_prng_init(void)
 #else
     last_pid = getpid();
 #endif
-    if (k5_get_os_entropy(osbuf, sizeof(osbuf))) {
+    if (k5_get_os_entropy(osbuf, sizeof(osbuf), 0)) {
         generator_reseed(&main_state, osbuf, sizeof(osbuf));
         have_entropy = TRUE;
     }
@@ -443,4 +443,28 @@ krb5_c_random_make_octets(krb5_context context, krb5_data *outdata)
     return 0;
 }
 
+krb5_error_code KRB5_CALLCONV
+krb5_c_random_os_entropy(krb5_context context, int strong, int *success)
+{
+    krb5_error_code ret;
+    krb5_data data;
+    uint8_t buf[64];
+    int status = 0;
+
+    if (!k5_get_os_entropy(buf, sizeof(buf), strong))
+        goto done;
+
+    data = make_data(buf, sizeof(buf));
+    ret = krb5_c_random_add_entropy(context, KRB5_C_RANDSOURCE_OSRAND, &data);
+    if (ret)
+        goto done;
+
+    status = 1;
+
+done:
+    if (success != NULL)
+        *success = status;
+    return 0;
+}
+
 #endif /* not TEST */
diff --git a/src/lib/crypto/krb/prng_os.c b/src/lib/crypto/krb/prng_os.c
index 730ed2e..ecfe351 100644
--- a/src/lib/crypto/krb/prng_os.c
+++ b/src/lib/crypto/krb/prng_os.c
@@ -91,3 +91,9 @@ krb5_c_random_make_octets(krb5_context context, krb5_data *outdata)
     }
     return 0;
 }
+
+krb5_error_code KRB5_CALLCONV
+krb5_c_random_os_entropy(krb5_context context, int strong, int *success)
+{
+    return 0;
+}