ssh: keep a successful rekey trigger out of ssh->error

- wolfSSH_TriggerKeyExchange() writes ssh->error only when
  SendKexInit() fails. It runs from HighwaterCheck() inside
  wolfSSH_SendPacket(), so writing WS_SUCCESS there erased what
  the pass the mark fired on had already reported.
- test_TriggerKeyExchangeKeepsError() seeds ssh->error and checks
  a rekey that starts cleanly leaves it alone.

Author: yosuke-wolfssl

src/ssh.c

@@ -1262,8 +1262,11 @@ int wolfSSH_TriggerKeyExchange(WOLFSSH* ssh)
     if (ret == WS_SUCCESS && SendAfterDisconnect(ssh))
         ret = WS_FATAL_ERROR;
 
-    if (ret == WS_SUCCESS)
-        ret = ssh->error = SendKexInit(ssh);
+    if (ret == WS_SUCCESS) {
+        ret = SendKexInit(ssh);
+        if (ret != WS_SUCCESS)
+            ssh->error = ret;
+    }
 
     WLOG(WS_LOG_DEBUG, "Leaving wolfSSH_TriggerKeyExchange(), ret = %d", ret);
     return ret;

tests/unit.c

@@ -7174,6 +7174,46 @@ static int test_StreamReadHeadOpenFailed(void)
 }
 #endif /* NO_WOLFSSH_CLIENT */
 
+#ifndef NO_WOLFSSH_CLIENT
+/* A rekey that starts cleanly leaves ssh->error alone. It runs from
+ * HighwaterCheck() inside wolfSSH_SendPacket(), so writing WS_SUCCESS there
+ * would erase what the pass the mark fired on had already reported. */
+static int test_TriggerKeyExchangeKeepsError(void)
+{
+    WOLFSSH_CTX* ctx = NULL;
+    WOLFSSH*     ssh = NULL;
+    int          result = 0;
+    int          ret;
+
+    ctx = wolfSSH_CTX_new(WOLFSSH_ENDPOINT_CLIENT, NULL);
+    if (ctx == NULL)
+        return -1795;
+    wolfSSH_SetIOSend(ctx, CountIoSend);
+    wolfSSH_SetIORecv(ctx, PacketIoRecv);
+
+    ssh = wolfSSH_new(ctx);
+    if (ssh == NULL) { result = -1796; goto done; }
+
+    /* The status the pass was carrying when the mark fired. */
+    ssh->error = WS_CHANNEL_CLOSED;
+
+    ret = wolfSSH_TriggerKeyExchange(ssh);
+    if (ret != WS_SUCCESS) { result = -1797; goto done; }
+    if (wolfSSH_get_error(ssh) != WS_CHANNEL_CLOSED) {
+        result = -1798;
+        goto done;
+    }
+
+done:
+    s_recvPkt = NULL;
+    s_recvPktSz = 0;
+    s_recvPktOff = 0;
+    wolfSSH_free(ssh);
+    wolfSSH_CTX_free(ctx);
+    return result;
+}
+#endif /* NO_WOLFSSH_CLIENT */
+
 
 /* A peer may half-close its channel before it makes its shell/exec/subsystem
  * request, RFC 4254 section 5.3. DoChannelEof() reports that as WS_EOF, and
@@ -20028,6 +20068,13 @@ int wolfSSH_UnitTest(int argc, char** argv)
            (unitResult == 0 ? "SUCCESS" : "FAILED"));
     testResult = testResult || unitResult;
 
+#ifndef NO_WOLFSSH_CLIENT
+    unitResult = test_TriggerKeyExchangeKeepsError();
+    printf("TriggerKeyExchangeKeepsError: %s\n",
+           (unitResult == 0 ? "SUCCESS" : "FAILED"));
+    testResult = testResult || unitResult;
+#endif
+
     unitResult = test_StreamReadExtDataHeadChannel();
     printf("StreamReadExtDataHeadChannel: %s\n",
            (unitResult == 0 ? "SUCCESS" : "FAILED"));