smtp: TLS upgrade fix

There were two places in the code that tried to connect the SSL filter,
e.g. do the TLS handshake, but only one changed stmp state to EHLO
afterwards.

Depending on timing, the wrong path was taken and the connection was
hanging, waiting for a server reply to a command not sent.

Do the upgrade to tls in one place and update connection filter and
smtps protocol handler at the same time. Always transition to EHLO on
success.

Fixes #16189
Reported-by: Christian Schmitz
Closes #16206

diff --git a/lib/smtp.c b/lib/smtp.c
index 7c631a1877858d2b7d5e9898dfb8d87e58165c8f..b763557a07d6c752ed60e21b175b48c0d8b28a1d 100644 (file)
--- a/lib/smtp.c
+++ b/lib/smtp.c
@@ -189,19 +189,6 @@ static const struct SASLproto saslsmtp = {
   SASL_FLAG_BASE64      /* Configuration flags */
 };
 
-#ifdef USE_SSL
-static void smtp_to_smtps(struct connectdata *conn)
-{
-  /* Change the connection handler */
-  conn->handler = &Curl_handler_smtps;
-
-  /* Set the connection's upgraded to TLS flag */
-  conn->bits.tls_upgraded = TRUE;
-}
-#else
-#define smtp_to_smtps(x) Curl_nop_stmt
-#endif
-
 /***********************************************************************
  *
  * smtp_endofresp()
@@ -396,31 +383,38 @@ static CURLcode smtp_perform_starttls(struct Curl_easy *data,
  */
 static CURLcode smtp_perform_upgrade_tls(struct Curl_easy *data)
 {
+#ifdef USE_SSL
   /* Start the SSL connection */
   struct connectdata *conn = data->conn;
   struct smtp_conn *smtpc = &conn->proto.smtpc;
   CURLcode result;
   bool ssldone = FALSE;
 
+  DEBUGASSERT(smtpc->state == SMTP_UPGRADETLS);
   if(!Curl_conn_is_ssl(conn, FIRSTSOCKET)) {
     result = Curl_ssl_cfilter_add(data, conn, FIRSTSOCKET);
     if(result)
       goto out;
+    /* Change the connection handler and SMTP state */
+    conn->handler = &Curl_handler_smtps;
+    conn->bits.tls_upgraded = TRUE;
   }
 
+  DEBUGASSERT(!smtpc->ssldone);
   result = Curl_conn_connect(data, FIRSTSOCKET, FALSE, &ssldone);
-  if(!result) {
+  DEBUGF(infof(data, "smtp_perform_upgrade_tls, connect -> %d, %d",
+           result, ssldone));
+  if(!result && ssldone) {
     smtpc->ssldone = ssldone;
-    if(smtpc->state != SMTP_UPGRADETLS)
-      smtp_state(data, SMTP_UPGRADETLS);
-
-    if(smtpc->ssldone) {
-      smtp_to_smtps(conn);
-      result = smtp_perform_ehlo(data);
-    }
+    /* perform EHLO now, changes smpt->state out of SMTP_UPGRADETLS */
+    result = smtp_perform_ehlo(data);
   }
 out:
   return result;
+#else
+  (void)data;
+  return CURLE_NOT_BUILT_IN;
+#endif
 }
 
 /***********************************************************************
@@ -875,7 +869,7 @@ static CURLcode smtp_state_starttls_resp(struct Curl_easy *data,
       result = smtp_perform_authentication(data);
   }
   else
-    result = smtp_perform_upgrade_tls(data);
+    smtp_state(data, SMTP_UPGRADETLS);
 
   return result;
 }
@@ -1204,8 +1198,11 @@ static CURLcode smtp_statemachine(struct Curl_easy *data,
 
   /* Busy upgrading the connection; right now all I/O is SSL/TLS, not SMTP */
 upgrade_tls:
-  if(smtpc->state == SMTP_UPGRADETLS)
-    return smtp_perform_upgrade_tls(data);
+  if(smtpc->state == SMTP_UPGRADETLS) {
+    result = smtp_perform_upgrade_tls(data);
+    if(result || (smtpc->state == SMTP_UPGRADETLS))
+      return result;
+  }
 
   /* Flush any data that needs to be sent */
   if(pp->sendleft)
@@ -1288,14 +1285,6 @@ static CURLcode smtp_multi_statemach(struct Curl_easy *data, bool *done)
   struct connectdata *conn = data->conn;
   struct smtp_conn *smtpc = &conn->proto.smtpc;
 
-  if(Curl_conn_is_ssl(conn, FIRSTSOCKET) && !smtpc->ssldone) {
-    bool ssldone = FALSE;
-    result = Curl_conn_connect(data, FIRSTSOCKET, FALSE, &ssldone);
-    smtpc->ssldone = ssldone;
-    if(result || !smtpc->ssldone)
-      return result;
-  }
-
   result = Curl_pp_statemach(data, &smtpc->pp, FALSE, FALSE);
   *done = (smtpc->state == SMTP_STOP);