internal: refuse userauth before service request

The server refuses user auth messages until the ssh-userauth service
request is in, per RFC 4252 section 1, and disconnects on them as on
any known id at the wrong time. A successful userauth request can no
longer satisfy the accept loop and draw SERVICE_ACCEPT for a service
the client never requested.

- IsMessageAllowedServer() gates ids 50 to 79 on acceptState reaching
  ACCEPT_CLIENT_USERAUTH_REQUEST_DONE
- regress: the filter refuses USERAUTH_REQUEST and INFO_RESPONSE when
  keyed and admits both after the service request
- regress: a userauth request with no service request disconnects
- regress: a userauth request pipelined behind the service request
  still gets SERVICE_ACCEPT, then its answer

Issue: #1287

Author: ejohnstown

src/internal.c

@@ -847,6 +847,16 @@ INLINE static int IsMessageAllowedServer(WOLFSSH *ssh, byte msg)
         }
     }
 
+    /* No userauth before the service request, RFC 4252 section 1.
+     * wolfSSH_accept() advances acceptState before reading again, so a
+     * pipelined request still passes. */
+    if (MSGIDLIMIT_AUTH(msg)
+            && ssh->acceptState < ACCEPT_CLIENT_USERAUTH_REQUEST_DONE) {
+        WLOG(WS_LOG_DEBUG, "Message ID %u not allowed by %s %s",
+                msg, "server", "before the service request");
+        return 0;
+    }
+
     /* Has client userauth started? */
     /* Allows the server to receive up to KEXDH GEX Request during KEX. */
     if (ssh->acceptState < ACCEPT_KEYED) {

src/ssh.c

@@ -761,6 +761,8 @@ int wolfSSH_accept(WOLFSSH* ssh)
                         return WS_FATAL_ERROR;
                     }
                 }
+                /* IsMessageAllowedServer() gates userauth on this; set it
+                 * before any further read. */
                 ssh->acceptState = ACCEPT_CLIENT_USERAUTH_REQUEST_DONE;
                 WLOG(WS_LOG_DEBUG, acceptState, "CLIENT_USERAUTH_REQUEST_DONE");
                 FALL_THROUGH;

tests/regress.c

@@ -5011,6 +5011,26 @@ static void TestServerUserauthBlockedBeforeKeyed(WOLFSSH* ssh)
 }
 
 
+/* Keyed is not enough: userauth waits for the service request. */
+static void TestServerUserauthBlockedBeforeServiceRequest(WOLFSSH* ssh)
+{
+    ResetSession(ssh);
+    ssh->acceptState = ACCEPT_KEYED;
+
+    AssertFalse(wolfSSH_TestIsMessageAllowed(ssh, MSGID_USERAUTH_REQUEST,
+            WS_MSG_RECV));
+    AssertFalse(wolfSSH_TestIsMessageAllowed(ssh,
+            MSGID_USERAUTH_INFO_RESPONSE, WS_MSG_RECV));
+
+    ssh->acceptState = ACCEPT_CLIENT_USERAUTH_REQUEST_DONE;
+
+    AssertTrue(wolfSSH_TestIsMessageAllowed(ssh, MSGID_USERAUTH_REQUEST,
+            WS_MSG_RECV));
+    AssertTrue(wolfSSH_TestIsMessageAllowed(ssh,
+            MSGID_USERAUTH_INFO_RESPONSE, WS_MSG_RECV));
+}
+
+
 /* One packet fed to a keyed but unauthenticated server. The cases below
  * differ only in the packet and the answer it draws. */
 static void RunServerMsgIdAtKeyed(const byte* pkt, word32 pktSz,
@@ -7910,6 +7930,82 @@ static void TestSameUserRetryAllowed(void)
     FreeChannelOpenHarness(&harness);
 }
 
+static int AcceptPasswordUserAuthCb(byte authType, WS_UserAuthData* authData,
+        void* ctx)
+{
+    (void)authData;
+    (void)ctx;
+
+    authCbInvoked = 1;
+    return (authType == WOLFSSH_USERAUTH_PASSWORD) ?
+            WOLFSSH_USERAUTH_SUCCESS : WOLFSSH_USERAUTH_FAILURE;
+}
+
+/* A userauth request without a service request draws a disconnect, not a
+ * SERVICE_ACCEPT, even with a password the callback accepts. */
+static void TestUserAuthBeforeServiceRequestDisconnects(void)
+{
+    ChannelOpenHarness harness;
+    byte in[128];
+    word32 inSz;
+
+    inSz = BuildUserAuthPasswordRequest("alice", "pw", in, sizeof(in));
+
+    ResetAuthCbRecord();
+    InitChannelOpenHarness(&harness, in, inSz);
+    wolfSSH_SetUserAuth(harness.ctx, AcceptPasswordUserAuthCb);
+    harness.ssh->acceptState = ACCEPT_KEYED;
+
+    AssertIntEQ(wolfSSH_accept(harness.ssh), WS_FATAL_ERROR);
+    AssertIntEQ(harness.ssh->error, WS_MSGID_NOT_ALLOWED_E);
+    AssertIntEQ(authCbInvoked, 0);
+    AssertIntEQ(harness.ssh->acceptState, ACCEPT_KEYED);
+    AssertTrue(harness.io.outSz > 0);
+    AssertIntEQ(ParseMsgId(harness.io.out, harness.io.outSz),
+            MSGID_DISCONNECT);
+    AssertTrue(harness.ssh->disconnected);
+
+    FreeChannelOpenHarness(&harness);
+}
+
+/* A userauth request queued right behind the service request draws
+ * SERVICE_ACCEPT, then its answer. */
+static void TestUserAuthPipelinedAfterServiceRequest(void)
+{
+    ChannelOpenHarness harness;
+    byte payload[32];
+    byte in[256];
+    word32 inSz;
+    word32 idx = 0;
+    word32 off;
+
+    idx = AppendString(payload, sizeof(payload), idx, "ssh-userauth");
+    inSz = WrapPacket(MSGID_SERVICE_REQUEST, payload, idx, in, sizeof(in));
+    inSz += BuildUserAuthPasswordRequest("alice", "pw",
+            in + inSz, sizeof(in) - inSz);
+
+    ResetAuthCbRecord();
+    InitChannelOpenHarness(&harness, in, inSz);
+    wolfSSH_SetUserAuth(harness.ctx, AcceptPasswordUserAuthCb);
+    harness.ssh->acceptState = ACCEPT_KEYED;
+
+    /* Stops for want of the channel open that would follow. */
+    AssertIntEQ(wolfSSH_accept(harness.ssh), WS_FATAL_ERROR);
+    AssertIntEQ(harness.ssh->error, WS_WANT_READ);
+    AssertIntEQ(authCbInvoked, 1);
+    AssertIntEQ(harness.ssh->acceptState, ACCEPT_SERVER_USERAUTH_SENT);
+    AssertIntEQ(harness.io.inOff, harness.io.inSz);
+    AssertIntEQ(ParseMsgId(harness.io.out, harness.io.outSz),
+            MSGID_SERVICE_ACCEPT);
+    off = NextPacketOffset(harness.io.out, harness.io.outSz);
+    AssertIntEQ(ParseMsgId(harness.io.out + off, harness.io.outSz - off),
+            MSGID_USERAUTH_SUCCESS);
+    off += NextPacketOffset(harness.io.out + off, harness.io.outSz - off);
+    AssertIntEQ(off, harness.io.outSz);
+
+    FreeChannelOpenHarness(&harness);
+}
+
 #ifdef WOLFSSH_KEYBOARD_INTERACTIVE
 static word32 BuildUserAuthKeyboardRequest(const char* user,
         byte* out, word32 outSz)
@@ -19042,6 +19138,7 @@ int main(int argc, char** argv)
     TestServerChannelBlockedBeforeAuth(serverSsh);
     TestServerChannelAllowedAfterAuth(serverSsh);
     TestServerUserauthBlockedBeforeKeyed(serverSsh);
+    TestServerUserauthBlockedBeforeServiceRequest(serverSsh);
     TestServerHighMsgIdBeforeAuthDisconnects();
     TestServerUnknownMsgIdBeforeAuthUnimplemented();
     TestServerKnownAuthMsgIdBeforeAuthDisconnects();
@@ -19111,6 +19208,8 @@ int main(int argc, char** argv)
     TestSecondSessionChannelRejected();
     TestUsernameChangeDisconnects();
     TestSameUserRetryAllowed();
+    TestUserAuthBeforeServiceRequestDisconnects();
+    TestUserAuthPipelinedAfterServiceRequest();
 #ifdef WOLFSSH_KEYBOARD_INTERACTIVE
     TestKbInfoResponseCountMismatchSendsFailure();
     TestKbInfoResponseMismatchKeepsFraming();