Remove ambiguity in rand_pool_add[_end] return value

When these two functions returned zero, it could mean:

1. that an error occured.  In their case, the error is an overflow of
   the pool, i.e. the correct response from the caller would be to
   stop trying to fill the pool.
2. that there isn't enought entropy acquired yet, i.e. the correct
   response from the caller would be to try and add more entropy to
   the pool.

Because of this ambiguity, the returned zero turns out to be useless.
This change makes the returned value more consistent.  1 means the
addition of new entropy was successful, 0 means it wasn't.  To know if
the pool has been filled enough, the caller will have to call some
other function, such as rand_pool_entropy_available().

Fixes #5846

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/5876)

4 files changed, 33 insertions, 32 deletions

diff --git a/crypto/rand/rand_lib.c b/crypto/rand/rand_lib.c
index 143dfb0f19..3589e75853 100644
--- a/crypto/rand/rand_lib.c
+++ b/crypto/rand/rand_lib.c
@@ -130,26 +130,20 @@ size_t rand_acquire_entropy_from_cpu(RAND_POOL *pool)
         buffer = rand_pool_add_begin(pool, bytes_needed);
 
         if (buffer != NULL) {
-
-            /* If RDSEED is available, use that. */
+            /* Whichever comes first, use RDSEED, RDRAND or nothing */
             if ((OPENSSL_ia32cap_P[2] & (1 << 18)) != 0) {
                 if (OPENSSL_ia32_rdseed_bytes(buffer, bytes_needed)
-                    == bytes_needed)
-                    return rand_pool_add_end(pool,
-                                             bytes_needed,
-                                             8 * bytes_needed);
-            }
-
-            /* Second choice is RDRAND. */
-            if ((OPENSSL_ia32cap_P[1] & (1 << (62 - 32))) != 0) {
+                    == bytes_needed) {
+                    rand_pool_add_end(pool, bytes_needed, 8 * bytes_needed);
+                }
+            } else if ((OPENSSL_ia32cap_P[1] & (1 << (62 - 32))) != 0) {
                 if (OPENSSL_ia32_rdrand_bytes(buffer, bytes_needed)
-                    == bytes_needed)
-                    return rand_pool_add_end(pool,
-                                             bytes_needed,
-                                             8 * bytes_needed);
+                    == bytes_needed) {
+                    rand_pool_add_end(pool, bytes_needed, 8 * bytes_needed);
+                }
+            } else {
+                rand_pool_add_end(pool, 0, 0);
             }
-
-            return rand_pool_add_end(pool, 0, 0);
         }
     }
 
@@ -222,7 +216,8 @@ size_t rand_drbg_get_entropy(RAND_DRBG *drbg,
                 bytes = bytes_needed;
             rand_drbg_unlock(drbg->parent);
 
-            entropy_available = rand_pool_add_end(pool, bytes, 8 * bytes);
+            rand_pool_add_end(pool, bytes, 8 * bytes);
+            entropy_available = rand_pool_entropy_available(pool);
         }
 
     } else {
@@ -631,11 +626,10 @@ size_t rand_pool_bytes_remaining(RAND_POOL *pool)
  * random input which contains at least |entropy| bits of
  * randomness.
  *
- * Return available amount of entropy after this operation.
- * (see rand_pool_entropy_available(pool))
+ * Returns 1 if the added amount is adequate, otherwise 0
  */
-size_t rand_pool_add(RAND_POOL *pool,
-                     const unsigned char *buffer, size_t len, size_t entropy)
+int rand_pool_add(RAND_POOL *pool,
+                  const unsigned char *buffer, size_t len, size_t entropy)
 {
     if (len > pool->max_len - pool->len) {
         RANDerr(RAND_F_RAND_POOL_ADD, RAND_R_ENTROPY_INPUT_TOO_LONG);
@@ -648,7 +642,7 @@ size_t rand_pool_add(RAND_POOL *pool,
         pool->entropy += entropy;
     }
 
-    return rand_pool_entropy_available(pool);
+    return 1;
 }
 
 /*
@@ -685,7 +679,7 @@ unsigned char *rand_pool_add_begin(RAND_POOL *pool, size_t len)
  * to the buffer which contain at least |entropy| bits of randomness.
  * It is allowed to add less bytes than originally reserved.
  */
-size_t rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy)
+int rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy)
 {
     if (len > pool->max_len - pool->len) {
         RANDerr(RAND_F_RAND_POOL_ADD_END, RAND_R_RANDOM_POOL_OVERFLOW);
@@ -697,7 +691,7 @@ size_t rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy)
         pool->entropy += entropy;
     }
 
-    return rand_pool_entropy_available(pool);
+    return 1;
 }
 
 int RAND_set_rand_method(const RAND_METHOD *meth)
diff --git a/crypto/rand/rand_unix.c b/crypto/rand/rand_unix.c
index b86f94ab72..0f9407f3ff 100644
--- a/crypto/rand/rand_unix.c
+++ b/crypto/rand/rand_unix.c
@@ -174,7 +174,8 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
         if (getrandom(buffer, bytes_needed, 0) == (int)bytes_needed)
             bytes = bytes_needed;
 
-        entropy_available = rand_pool_add_end(pool, bytes, 8 * bytes);
+        rand_pool_add_end(pool, bytes, 8 * bytes);
+        entropy_available = rand_pool_entropy_available(pool);
     }
     if (entropy_available > 0)
         return entropy_available;
@@ -203,7 +204,8 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
                 if (fread(buffer, 1, bytes_needed, fp) == bytes_needed)
                     bytes = bytes_needed;
 
-                entropy_available = rand_pool_add_end(pool, bytes, 8 * bytes);
+                rand_pool_add_end(pool, bytes, 8 * bytes);
+                entropy_available = rand_pool_entropy_available(pool);
             }
             fclose(fp);
             if (entropy_available > 0)
@@ -241,7 +243,8 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
                 if (num == (int)bytes_needed)
                     bytes = bytes_needed;
 
-                entropy_available = rand_pool_add_end(pool, bytes, 8 * bytes);
+                rand_pool_add_end(pool, bytes, 8 * bytes);
+                entropy_available = rand_pool_entropy_available(pool);
             }
             if (entropy_available > 0)
                 return entropy_available;
diff --git a/crypto/rand/rand_vms.c b/crypto/rand/rand_vms.c
index 7edec9ebd2..1507c6ff7c 100644
--- a/crypto/rand/rand_vms.c
+++ b/crypto/rand/rand_vms.c
@@ -148,8 +148,9 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
     if (total_length > bytes_remaining)
         total_length = bytes_remaining;
 
-    return rand_pool_add(pool, (PTR_T)data_buffer, total_length,
-                         total_length * ENTROPY_BITS_PER_BYTE);
+    rand_pool_add(pool, (PTR_T)data_buffer, total_length,
+                  total_length * ENTROPY_BITS_PER_BYTE);
+    return rand_pool_entropy_available(pool);
 }
 
 #endif
diff --git a/crypto/rand/rand_win.c b/crypto/rand/rand_win.c
index 7f34188107..ad5e3d116b 100644
--- a/crypto/rand/rand_win.c
+++ b/crypto/rand/rand_win.c
@@ -70,7 +70,8 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
             BCRYPT_USE_SYSTEM_PREFERRED_RNG) == STATUS_SUCCESS)
             bytes = bytes_needed;
 
-        entropy_available = rand_pool_add_end(pool, bytes, 8 * bytes);
+        rand_pool_add_end(pool, bytes, 8 * bytes);
+        entropy_available = rand_pool_entropy_available(pool);
     }
     if (entropy_available > 0)
         return entropy_available;
@@ -88,7 +89,8 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
             CryptReleaseContext(hProvider, 0);
         }
 
-        entropy_available = rand_pool_add_end(pool, bytes, 8 * bytes);
+        rand_pool_add_end(pool, bytes, 8 * bytes);
+        entropy_available = rand_pool_entropy_available(pool);
     }
     if (entropy_available > 0)
         return entropy_available;
@@ -106,7 +108,8 @@ size_t rand_pool_acquire_entropy(RAND_POOL *pool)
 
             CryptReleaseContext(hProvider, 0);
         }
-        entropy_available = rand_pool_add_end(pool, bytes, 8 * bytes);
+        rand_pool_add_end(pool, bytes, 8 * bytes);
+        entropy_available = rand_pool_entropy_available(pool);
     }
     if (entropy_available > 0)
         return entropy_available;