Work around language and compiler bug in memcpy, etc.

Most C standard library functions are undefined if passed NULL, even
when the corresponding length is zero. This gives them (and, in turn,
all functions which call them) surprising behavior on empty arrays.
Some compilers will miscompile code due to this rule. See also
https://www.imperialviolet.org/2016/06/26/nonnull.html

Add OPENSSL_memcpy, etc., wrappers which avoid this problem.

BUG=23

Change-Id: I95f42b23e92945af0e681264fffaf578e7f8465e
Reviewed-on: https://boringssl-review.googlesource.com/12928
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>

ssl/ssl_session.c

diff --git a/ssl/ssl_session.c b/ssl/ssl_session.c
index d6d7dab..62ee28e 100644
--- a/ssl/ssl_session.c
+++ b/ssl/ssl_session.c
@@ -166,7 +166,7 @@
     OPENSSL_PUT_ERROR(SSL, ERR_R_MALLOC_FAILURE);
     return 0;
   }
-  memset(session, 0, sizeof(SSL_SESSION));
+  OPENSSL_memset(session, 0, sizeof(SSL_SESSION));
 
   session->verify_result = X509_V_ERR_INVALID_CALL;
   session->references = 1;
@@ -185,11 +185,11 @@
   new_session->is_server = session->is_server;
   new_session->ssl_version = session->ssl_version;
   new_session->sid_ctx_length = session->sid_ctx_length;
-  memcpy(new_session->sid_ctx, session->sid_ctx, session->sid_ctx_length);
+  OPENSSL_memcpy(new_session->sid_ctx, session->sid_ctx, session->sid_ctx_length);
 
   /* Copy the key material. */
   new_session->master_key_length = session->master_key_length;
-  memcpy(new_session->master_key, session->master_key,
+  OPENSSL_memcpy(new_session->master_key, session->master_key,
          session->master_key_length);
   new_session->cipher = session->cipher;
 
@@ -245,7 +245,8 @@
     }
   }
 
-  memcpy(new_session->peer_sha256, session->peer_sha256, SHA256_DIGEST_LENGTH);
+  OPENSSL_memcpy(new_session->peer_sha256, session->peer_sha256,
+                 SHA256_DIGEST_LENGTH);
   new_session->peer_sha256_valid = session->peer_sha256_valid;
 
   if (session->tlsext_hostname != NULL) {
@@ -263,14 +264,14 @@
   /* Copy non-authentication connection properties. */
   if (dup_flags & SSL_SESSION_INCLUDE_NONAUTH) {
     new_session->session_id_length = session->session_id_length;
-    memcpy(new_session->session_id, session->session_id,
-           session->session_id_length);
+    OPENSSL_memcpy(new_session->session_id, session->session_id,
+                   session->session_id_length);
 
     new_session->group_id = session->group_id;
 
-    memcpy(new_session->original_handshake_hash,
-           session->original_handshake_hash,
-           session->original_handshake_hash_len);
+    OPENSSL_memcpy(new_session->original_handshake_hash,
+                   session->original_handshake_hash,
+                   session->original_handshake_hash_len);
     new_session->original_handshake_hash_len =
         session->original_handshake_hash_len;
     new_session->tlsext_tick_lifetime_hint = session->tlsext_tick_lifetime_hint;
@@ -387,7 +388,7 @@
   if (max_out > (size_t)session->master_key_length) {
     max_out = (size_t)session->master_key_length;
   }
-  memcpy(out, session->master_key, max_out);
+  OPENSSL_memcpy(out, session->master_key, max_out);
   return max_out;
 }
 
@@ -418,7 +419,7 @@
 
   assert(sizeof(session->sid_ctx) < 256);
   session->sid_ctx_length = (uint8_t)sid_ctx_len;
-  memcpy(session->sid_ctx, sid_ctx, sid_ctx_len);
+  OPENSSL_memcpy(session->sid_ctx, sid_ctx, sid_ctx_len);
 
   return 1;
 }
@@ -517,7 +518,7 @@
     OPENSSL_PUT_ERROR(SSL, ERR_R_INTERNAL_ERROR);
     goto err;
   }
-  memcpy(session->sid_ctx, ssl->sid_ctx, ssl->sid_ctx_length);
+  OPENSSL_memcpy(session->sid_ctx, ssl->sid_ctx, ssl->sid_ctx_length);
   session->sid_ctx_length = ssl->sid_ctx_length;
 
   /* The session is marked not resumable until it is completely filled in. */
@@ -627,7 +628,7 @@
                       NULL)) {
       goto err;
     }
-    memcpy(key_name, tctx->tlsext_tick_key_name, 16);
+    OPENSSL_memcpy(key_name, tctx->tlsext_tick_key_name, 16);
   }
 
   uint8_t *ptr;
@@ -639,7 +640,7 @@
 
   size_t total = 0;
 #if defined(BORINGSSL_UNSAFE_FUZZER_MODE)
-  memcpy(ptr, session_buf, session_len);
+  OPENSSL_memcpy(ptr, session_buf, session_len);
   total = session_len;
 #else
   int len;
@@ -679,7 +680,8 @@
   }
 
   return session->sid_ctx_length == ssl->sid_ctx_length &&
-         memcmp(session->sid_ctx, ssl->sid_ctx, ssl->sid_ctx_length) == 0;
+         OPENSSL_memcmp(session->sid_ctx, ssl->sid_ctx, ssl->sid_ctx_length) ==
+             0;
 }
 
 int ssl_session_is_time_valid(const SSL *ssl, const SSL_SESSION *session) {
@@ -737,7 +739,7 @@
     SSL_SESSION data;
     data.ssl_version = ssl->version;
     data.session_id_length = session_id_len;
-    memcpy(data.session_id, session_id, session_id_len);
+    OPENSSL_memcpy(data.session_id, session_id, session_id_len);
 
     CRYPTO_MUTEX_lock_read(&ssl->initial_ctx->lock);
     session = lh_SSL_SESSION_retrieve(ssl->initial_ctx->sessions, &data);