Harden IMAP and POP TLS state handling

docs/imap.md

@@ -37,6 +37,10 @@ ad-hoc downgrade.
 AUTH capabilities are generated from the GNU GSASL mechanisms which Bongo
 has actually enabled. Password mechanisms are advertised only on a TLS
 connection; unencrypted connections offer STARTTLS and keep LOGIN disabled.
+STARTTLS rejects arguments and repeated or post-authentication use, discards
+already buffered cleartext before the TLS handshake, and closes the connection
+without attempting a plaintext IMAP response if negotiation fails. A client
+which ignores `LOGINDISABLED` receives a tagged `NO` without a password lookup.
 
 Relevant standards are [RFC 9051](https://www.rfc-editor.org/rfc/rfc9051.html),
 [RFC 3501](https://www.rfc-editor.org/rfc/rfc3501.html),

docs/protocols.md

@@ -34,6 +34,10 @@ POP3 implements the normal transaction commands and advertises `TOP`,
 `RESP-CODES`, `AUTH-RESP-CODE`, `PIPELINING`, `EXPIRE NEVER`, `UIDL`, and
 `UTF8`. STLS is offered before authentication; SASL and password login are
 advertised only according to the TLS policy. POP3S provides implicit TLS.
+After a successful `UTF8` command, `STLS` is no longer advertised and is
+rejected so that the negotiated UTF-8 session state cannot cross into TLS.
+Both IMAP STARTTLS and POP3 STLS discard buffered cleartext before negotiating
+TLS.
 
 ## Server-side filtering
 

docs/release-testing-0.7.md

@@ -154,7 +154,7 @@ inputs and outputs is absent from the ZIP.
 | ID | Test | R1 | R2 | R3 |
 | --- | --- | --- | --- | --- |
 | IMAP-01 | Capability list matches implemented rev2/rev1/legacy behaviour |  |  |  |
-| IMAP-02 | Port 143 STARTTLS and pre-TLS `LOGINDISABLED` |  |  |  |
+| IMAP-02 | Port 143 STARTTLS, pre-TLS `LOGINDISABLED`, tagged `NO` for plaintext LOGIN, repeated STARTTLS rejection |  |  |  |
 | IMAP-03 | Port 993 TLS, LOGIN, SASL PLAIN, and SASL LOGIN |  |  |  |
 | IMAP-04 | CAPABILITY, NOOP, LOGOUT, ID, and NAMESPACE |  |  |  |
 | IMAP-05 | LIST, LSUB, extended LIST, LIST-STATUS, hierarchy quoting |  |  |  |
@@ -171,18 +171,18 @@ inputs and outputs is absent from the ZIP.
 | IMAP-16 | ENABLE UTF8=ACCEPT and UTF-8 mailbox/message names |  |  |  |
 | IMAP-17 | SPECIAL-USE and CREATE-SPECIAL-USE folders |  |  |  |
 | IMAP-18 | Old-client plain IMAP4 subset without rev1/rev2 assumptions |  |  |  |
-| IMAP-19 | Invalid states, malformed sets/literals, oversized/pipelined input |  |  |  |
+| IMAP-19 | Invalid states, malformed sets/literals, oversized input, and STARTTLS plaintext-pipeline injection resistance |  |  |  |
 | IMAP-20 | Reconnect, simultaneous clients, restart, mailbox consistency |  |  |  |
 
 ## POP3 and ManageSieve
 
 | ID | Test | R1 | R2 | R3 |
 | --- | --- | --- | --- | --- |
-| POP-01 | Port 110 CAPA/STLS; credentials unavailable before TLS |  |  |  |
+| POP-01 | Port 110 CAPA/STLS; credentials unavailable before TLS; buffered plaintext discarded |  |  |  |
 | POP-02 | Port 995 TLS with USER/PASS and shared GSASL mechanisms |  |  |  |
 | POP-03 | STAT, LIST, UIDL, RETR, TOP, and dot transparency |  |  |  |
 | POP-04 | DELE, RSET, NOOP, QUIT commit, and disconnect rollback |  |  |  |
-| POP-05 | UTF8, PIPELINING, response codes, malformed input, timeout |  |  |  |
+| POP-05 | UTF8, STLS rejection after UTF8, PIPELINING, response codes, malformed input, timeout |  |  |  |
 | SIEVE-01 | Port 4190 greeting, STARTTLS, and GSASL authentication |  |  |  |
 | SIEVE-02 | CAPABILITY, HAVESPACE, PUT/CHECK/LIST/GETSCRIPT |  |  |  |
 | SIEVE-03 | SETACTIVE, RENAME, DELETE, LOGOUT, and persistence |  |  |  |

src/agents/imap/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_executable(bongoimap
 	imapd.c
 	capabilities.c
+	protocol.c
 	enable.c
 	utf8-mailbox.c
 	append-message.c
@@ -46,6 +47,15 @@ if(BUILD_TESTING)
 	)
 	add_test(NAME imap-capabilities COMMAND imap-capabilities-test)
 
+	add_executable(imap-protocol-test
+		tests/protocol-test.c
+		protocol.c
+	)
+	target_include_directories(imap-protocol-test PRIVATE
+		${CMAKE_CURRENT_SOURCE_DIR}
+	)
+	add_test(NAME imap-protocol COMMAND imap-protocol-test)
+
 	add_executable(imap-enable-test
 		tests/enable-test.c
 		enable.c

src/agents/imap/imapd.h

@@ -98,6 +98,8 @@ typedef enum {
     STATUS_INVALID_ARGUMENT,
     STATUS_INVALID_STATE,
     STATUS_UNKNOWN_COMMAND,
+    STATUS_LOGIN_DISABLED,
+    STATUS_TLS_UNAVAILABLE,
     STATUS_TLS_NEGOTIATION_FAILURE,
     STATUS_CHARSET_NOT_SUPPORTED,
     STATUS_UID_NOT_FOUND,
@@ -156,6 +158,8 @@ static ImapErrorString ImapErrorStrings[] = {
     { STATUS_INVALID_ARGUMENT,                   "%s BAD %s invalid arguments\r\n" },
     { STATUS_INVALID_STATE,                      "%s BAD %s invalid command in current state\r\n" },
     { STATUS_UNKNOWN_COMMAND,                    "* BAD command unrecognized\r\n" },
+    { STATUS_LOGIN_DISABLED,                     "%s NO %s plaintext LOGIN disabled; use STARTTLS\r\n" },
+    { STATUS_TLS_UNAVAILABLE,                    "%s NO %s TLS unavailable\r\n" },
     { STATUS_TLS_NEGOTIATION_FAILURE,            "%s BAD %s negotiation failed\r\n" },
     { 0, NULL }
 };

src/agents/imap/protocol.c

@@ -0,0 +1,57 @@
+/****************************************************************************
+ * <Novell-copyright>
+ * Copyright (c) 2001 Novell, Inc. All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, contact Novell, Inc.
+ *
+ * To contact Novell about this file by physical or electronic mail, you
+ * may find current contact information at www.novell.com.
+ * </Novell-copyright>
+ ****************************************************************************/
+
+#include "protocol.h"
+
+#include <ctype.h>
+#include <string.h>
+
+static int
+EqualsIgnoreCase(const char *left, const char *right)
+{
+    if (!left || !right) return 0;
+    while (*left && *right) {
+        if (toupper((unsigned char)*left) != toupper((unsigned char)*right))
+            return 0;
+        left++;
+        right++;
+    }
+    return *left == '\0' && *right == '\0';
+}
+
+IMAPStartTlsStatus
+IMAPStartTlsCheck(const char *command_line, int authenticated,
+                  int tls_active, int tls_available)
+{
+    if (!EqualsIgnoreCase(command_line, "STARTTLS"))
+        return IMAP_STARTTLS_INVALID_ARGUMENTS;
+    if (authenticated || tls_active) return IMAP_STARTTLS_INVALID_STATE;
+    if (!tls_available) return IMAP_STARTTLS_UNAVAILABLE;
+    return IMAP_STARTTLS_READY;
+}
+
+IMAPLoginStatus
+IMAPLoginCheck(int authenticated, int tls_active)
+{
+    if (authenticated) return IMAP_LOGIN_INVALID_STATE;
+    if (!tls_active) return IMAP_LOGIN_DISABLED;
+    return IMAP_LOGIN_READY;
+}

src/agents/imap/protocol.h

@@ -0,0 +1,43 @@
+/****************************************************************************
+ * <Novell-copyright>
+ * Copyright (c) 2001 Novell, Inc. All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, contact Novell, Inc.
+ *
+ * To contact Novell about this file by physical or electronic mail, you
+ * may find current contact information at www.novell.com.
+ * </Novell-copyright>
+ ****************************************************************************/
+
+#ifndef BONGO_IMAP_PROTOCOL_H
+#define BONGO_IMAP_PROTOCOL_H
+
+typedef enum {
+    IMAP_STARTTLS_READY = 0,
+    IMAP_STARTTLS_INVALID_ARGUMENTS,
+    IMAP_STARTTLS_INVALID_STATE,
+    IMAP_STARTTLS_UNAVAILABLE
+} IMAPStartTlsStatus;
+
+typedef enum {
+    IMAP_LOGIN_READY = 0,
+    IMAP_LOGIN_DISABLED,
+    IMAP_LOGIN_INVALID_STATE
+} IMAPLoginStatus;
+
+IMAPStartTlsStatus IMAPStartTlsCheck(const char *command_line,
+                                     int authenticated, int tls_active,
+                                     int tls_available);
+IMAPLoginStatus IMAPLoginCheck(int authenticated, int tls_active);
+
+#endif

src/agents/imap/session.c

@@ -29,6 +29,7 @@
 #include <bongosasl.h>
 
 #include "imapd.h"
+#include "protocol.h"
 
 void
 ImapAnnotateAliasClient(ImapSession *session)
@@ -298,10 +299,20 @@ ImapCommandLogin(void *param)
 {
     ImapSession *session = (ImapSession *)param;
     long ccode;
+    IMAPLoginStatus status;
     char *username = NULL;
     char *password = NULL;
 
-    if (session->client.state == STATE_FRESH && session->client.conn->ssl.enable) {
+    status = IMAPLoginCheck(session->client.state >= STATE_AUTH,
+                            session->client.conn->ssl.enable);
+    if (status == IMAP_LOGIN_DISABLED)
+        return(SendError(session->client.conn, session->command.tag, "LOGIN",
+                         STATUS_LOGIN_DISABLED));
+    if (status == IMAP_LOGIN_INVALID_STATE)
+        return(SendError(session->client.conn, session->command.tag, "LOGIN",
+                         STATUS_INVALID_STATE));
+
+    if (status == IMAP_LOGIN_READY) {
         ccode = GrabTwoArguments(session, session->command.buffer + 6, &username, &password);
         if (ccode == STATUS_CONTINUE) {
             X500Encode(username);
@@ -335,27 +346,48 @@ int
 ImapCommandStartTls(void *param)
 {
     long ccode;
+    IMAPStartTlsStatus status;
 
     ImapSession *session = (ImapSession *)param;
 
-    if (session->client.state < STATE_AUTH) {
-        if (Imap.server.ssl.config.options) {
-            if (((ccode = ConnWriteF(session->client.conn, "%s OK Begin TLS negotiation\r\n",session->command.tag)) != -1) && (ccode = ConnFlush(session->client.conn))) {
-                session->client.conn->ssl.enable = TRUE;    
-                if (ConnNegotiate(session->client.conn, Imap.server.ssl.context)) {
-                    return(STATUS_CONTINUE);
-                }
+    status = IMAPStartTlsCheck(session->command.buffer,
+                               session->client.state >= STATE_AUTH,
+                               session->client.conn->ssl.enable,
+                               Imap.server.ssl.context != NULL);
+    if (status == IMAP_STARTTLS_INVALID_ARGUMENTS)
+        return(SendError(session->client.conn, session->command.tag,
+                         "STARTTLS", STATUS_INVALID_ARGUMENT));
+    if (status == IMAP_STARTTLS_INVALID_STATE)
+        return(SendError(session->client.conn, session->command.tag,
+                         "STARTTLS", STATUS_INVALID_STATE));
+    if (status == IMAP_STARTTLS_UNAVAILABLE)
+        return(SendError(session->client.conn, session->command.tag,
+                         "STARTTLS", STATUS_TLS_UNAVAILABLE));
 
-                return(SendError(session->client.conn, session->command.tag, "STARTTLS", STATUS_TLS_NEGOTIATION_FAILURE));
-            } 
+    ccode = ConnWriteF(session->client.conn,
+                       "%s OK Begin TLS negotiation\r\n",
+                       session->command.tag);
+    if (ccode == -1 || ConnFlush(session->client.conn) == -1)
+        return(STATUS_ABORT);
 
-            return(STATUS_ABORT);
-        }
-
-        return(SendError(session->client.conn, session->command.tag, "", STATUS_UNKNOWN_COMMAND));
-    }
-
-    return(SendError(session->client.conn, session->command.tag, "STARTTLS", STATUS_INVALID_STATE));
+    /*
+     * Never carry pipelined cleartext across STARTTLS.  RFC 9051 requires
+     * extra bytes already received after the command to become TLS input or
+     * to be discarded.  Discarding them avoids plaintext command injection
+     * and matches the POP3 STLS path.
+     */
+    session->client.conn->receive.read =
+        session->client.conn->receive.write =
+            session->client.conn->receive.buffer;
+    session->client.conn->receive.remaining = CONN_TCP_MTU;
+    session->client.conn->receive.buffer[0] = '\0';
+    session->client.conn->ssl.enable = TRUE;
+    session->client.enabledCapabilities = 0;
 
+    if (ConnNegotiate(session->client.conn, Imap.server.ssl.context))
+        return(STATUS_CONTINUE);
 
+    /* TLS bytes may already have been exchanged; no IMAP response is safe. */
+    ConnClose(session->client.conn);
+    return(STATUS_ABORT);
 }

src/agents/imap/tests/protocol-test.c

@@ -0,0 +1,46 @@
+/****************************************************************************
+ * <Novell-copyright>
+ * Copyright (c) 2001 Novell, Inc. All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, contact Novell, Inc.
+ *
+ * To contact Novell about this file by physical or electronic mail, you
+ * may find current contact information at www.novell.com.
+ * </Novell-copyright>
+ ****************************************************************************/
+
+#include "protocol.h"
+
+#include <assert.h>
+
+int
+main(void)
+{
+    assert(IMAPStartTlsCheck("STARTTLS", 0, 0, 1) == IMAP_STARTTLS_READY);
+    assert(IMAPStartTlsCheck("starttls", 0, 0, 1) == IMAP_STARTTLS_READY);
+    assert(IMAPStartTlsCheck("STARTTLS ", 0, 0, 1) ==
+           IMAP_STARTTLS_INVALID_ARGUMENTS);
+    assert(IMAPStartTlsCheck("STARTTLS extra", 0, 0, 1) ==
+           IMAP_STARTTLS_INVALID_ARGUMENTS);
+    assert(IMAPStartTlsCheck("STARTTLS", 1, 0, 1) ==
+           IMAP_STARTTLS_INVALID_STATE);
+    assert(IMAPStartTlsCheck("STARTTLS", 0, 1, 1) ==
+           IMAP_STARTTLS_INVALID_STATE);
+    assert(IMAPStartTlsCheck("STARTTLS", 0, 0, 0) ==
+           IMAP_STARTTLS_UNAVAILABLE);
+    assert(IMAPLoginCheck(0, 1) == IMAP_LOGIN_READY);
+    assert(IMAPLoginCheck(0, 0) == IMAP_LOGIN_DISABLED);
+    assert(IMAPLoginCheck(1, 1) == IMAP_LOGIN_INVALID_STATE);
+    assert(IMAPLoginCheck(1, 0) == IMAP_LOGIN_INVALID_STATE);
+    return 0;
+}

src/agents/pop/capabilities.c

@@ -47,6 +47,7 @@ Append(char *buffer, size_t buffer_size, size_t *length,
 size_t
 POP3FormatCapabilities(char *buffer, size_t buffer_size,
                        int authorization_state, int tls_active,
+                       int utf8_active,
                        int stls_available,
                        const char *sasl_mechanisms)
 {
@@ -63,7 +64,8 @@ POP3FormatCapabilities(char *buffer, size_t buffer_size,
                  sasl_mechanisms)) ||
         (authorization_state && tls_active &&
          !Append(buffer, buffer_size, &length, "USER\r\n")) ||
-        (authorization_state && !tls_active && stls_available &&
+        (authorization_state && !tls_active && !utf8_active &&
+         stls_available &&
          !Append(buffer, buffer_size, &length, "STLS\r\n")) ||
         !Append(buffer, buffer_size, &length, ".\r\n"))
         return 0;

src/agents/pop/capabilities.h

@@ -27,6 +27,7 @@
 /* Returns the number of bytes written, or 0 if the buffer was too small. */
 size_t POP3FormatCapabilities(char *buffer, size_t buffer_size,
                               int authorization_state, int tls_active,
+                              int utf8_active,
                               int stls_available,
                               const char *sasl_mechanisms);
 

src/agents/pop/pop3.c

@@ -1136,7 +1136,7 @@ POP3CommandCapa(void *param)
     }
     capabilityLength = POP3FormatCapabilities(
         client->buffer, sizeof(client->buffer), authorizationState,
-        client->conn->ssl.enable,
+        client->conn->ssl.enable, client->utf8Mode,
         POP3.server.ssl.enable && POP3.server.ssl.context != NULL, mechanisms);
     ccode = capabilityLength
         ? ConnWrite(client->conn, client->buffer, capabilityLength)
@@ -1533,6 +1533,7 @@ POP3CommandSTLS(void *param)
 {
     int ccode;
     BOOL result;
+    POP3STLSStatus status;
     POP3Client *client = (POP3Client *)param;
 
     if (!POP3ArgumentsEmpty(client->command +
@@ -1544,19 +1545,19 @@ POP3CommandSTLS(void *param)
         return ConnWrite(client->conn, MSGERRSYNTAX,
                          sizeof(MSGERRSYNTAX) - 1);
 
-    if ((client->state == POP3_CLIENT_FRESH ||
-         client->state == POP3_CLIENT_AUTHORIZATION) &&
-        !client->conn->ssl.enable) {
-        if (POP3.server.ssl.enable && POP3.server.ssl.context) {
-            ccode = ConnWrite(client->conn, MSGOKSTARTTLS, sizeof(MSGOKSTARTTLS) - 1);
-        } else {
-            return ConnWrite(client->conn,
-                             "-ERR [SYS/PERM] TLS unavailable\r\n",
-                             sizeof("-ERR [SYS/PERM] TLS unavailable\r\n") - 1);
-        }
-    } else {
+    status = POP3STLSCheck(client->state == POP3_CLIENT_FRESH ||
+                               client->state == POP3_CLIENT_AUTHORIZATION,
+                           client->conn->ssl.enable, client->utf8Mode,
+                           POP3.server.ssl.enable && POP3.server.ssl.context);
+    if (status == POP3_STLS_INVALID_STATE) {
         return(ConnWrite(client->conn, MSGERRBADSTATE, sizeof(MSGERRBADSTATE) - 1));
     }
+    if (status == POP3_STLS_UNAVAILABLE)
+        return ConnWrite(client->conn,
+                         "-ERR [SYS/PERM] TLS unavailable\r\n",
+                         sizeof("-ERR [SYS/PERM] TLS unavailable\r\n") - 1);
+
+    ccode = ConnWrite(client->conn, MSGOKSTARTTLS, sizeof(MSGOKSTARTTLS) - 1);
 
     if (ccode != -1) {
         ccode = ConnFlush(client->conn);

src/agents/pop/protocol.c

@@ -57,6 +57,16 @@ POP3ArgumentsEmpty(const char *arguments)
     return arguments && *arguments == '\0';
 }
 
+POP3STLSStatus
+POP3STLSCheck(int authorization_state, int tls_active, int utf8_active,
+              int tls_available)
+{
+    if (!authorization_state || tls_active || utf8_active)
+        return POP3_STLS_INVALID_STATE;
+    if (!tls_available) return POP3_STLS_UNAVAILABLE;
+    return POP3_STLS_READY;
+}
+
 int
 POP3ParseMessageNumber(const char *arguments, uint32_t *message_number)
 {

src/agents/pop/protocol.h

@@ -35,10 +35,18 @@ typedef struct {
     int ends_in_cr;
 } POP3MultilineWriter;
 
+typedef enum {
+    POP3_STLS_READY = 0,
+    POP3_STLS_INVALID_STATE,
+    POP3_STLS_UNAVAILABLE
+} POP3STLSStatus;
+
 int POP3Contains8Bit(const void *data, size_t length);
 int POP3UTF8Valid(const void *data, size_t length);
 
 int POP3ArgumentsEmpty(const char *arguments);
+POP3STLSStatus POP3STLSCheck(int authorization_state, int tls_active,
+                            int utf8_active, int tls_available);
 int POP3ParseMessageNumber(const char *arguments, uint32_t *message_number);
 int POP3ParseTopArguments(const char *arguments, uint32_t *message_number,
                           uint32_t *line_count);

src/agents/pop/tests/capabilities-test.c

@@ -30,29 +30,35 @@ main(void)
     char buffer[1024];
     char small[8];
 
-    assert(POP3FormatCapabilities(buffer, sizeof(buffer), 1, 0, 0, NULL) > 0);
+    assert(POP3FormatCapabilities(buffer, sizeof(buffer), 1, 0, 0, 0,
+                                  NULL) > 0);
     assert(!strstr(buffer, "STLS"));
     assert(!strstr(buffer, "SASL"));
     assert(!strstr(buffer, "USER"));
     assert(strstr(buffer, "UTF8\r\n"));
 
-    assert(POP3FormatCapabilities(buffer, sizeof(buffer), 1, 0, 1, NULL) > 0);
+    assert(POP3FormatCapabilities(buffer, sizeof(buffer), 1, 0, 0, 1,
+                                  NULL) > 0);
     assert(strstr(buffer, "STLS\r\n"));
     assert(!strstr(buffer, "SASL"));
 
-    assert(POP3FormatCapabilities(buffer, sizeof(buffer), 1, 1, 1,
+    assert(POP3FormatCapabilities(buffer, sizeof(buffer), 1, 1, 0, 1,
                                   "PLAIN LOGIN") > 0);
     assert(!strstr(buffer, "STLS"));
     assert(strstr(buffer, "SASL PLAIN LOGIN\r\n"));
     assert(strstr(buffer, "USER\r\n"));
 
-    assert(POP3FormatCapabilities(buffer, sizeof(buffer), 0, 1, 1,
+    assert(POP3FormatCapabilities(buffer, sizeof(buffer), 0, 1, 0, 1,
                                   "PLAIN LOGIN") > 0);
     assert(!strstr(buffer, "STLS"));
     assert(strstr(buffer, "SASL PLAIN LOGIN\r\n"));
     assert(!strstr(buffer, "USER"));
 
-    assert(POP3FormatCapabilities(small, sizeof(small), 1, 1, 1,
+    assert(POP3FormatCapabilities(buffer, sizeof(buffer), 1, 0, 1, 1,
+                                  NULL) > 0);
+    assert(!strstr(buffer, "STLS"));
+
+    assert(POP3FormatCapabilities(small, sizeof(small), 1, 1, 0, 1,
                                   "PLAIN LOGIN") == 0);
     assert(small[0] == '\0');
     return 0;

src/agents/pop/tests/protocol-test.c

@@ -49,6 +49,11 @@ TestArguments(void)
 
     assert(POP3ArgumentsEmpty(""));
     assert(!POP3ArgumentsEmpty(" "));
+    assert(POP3STLSCheck(1, 0, 0, 1) == POP3_STLS_READY);
+    assert(POP3STLSCheck(0, 0, 0, 1) == POP3_STLS_INVALID_STATE);
+    assert(POP3STLSCheck(1, 1, 0, 1) == POP3_STLS_INVALID_STATE);
+    assert(POP3STLSCheck(1, 0, 1, 1) == POP3_STLS_INVALID_STATE);
+    assert(POP3STLSCheck(1, 0, 0, 0) == POP3_STLS_UNAVAILABLE);
     assert(POP3ParseMessageNumber(" 1", &message) && message == 1);
     assert(POP3ParseMessageNumber("\t4294967295", &message) &&
            message == UINT32_MAX);