ssh: add generic request callbacks

src/agent.c

@@ -1731,6 +1731,91 @@ int wolfSSH_AGENT_enable(WOLFSSH* ssh, byte isEnabled)
 }
 
 
+int wolfSSH_AGENT_ChannelOpen(WOLFSSH* ssh)
+{
+    WOLFSSH_AGENT_CTX* newAgent = NULL;
+    WOLFSSH_CHANNEL* newChannel = NULL;
+    int ret = WS_SUCCESS;
+    /* wolfSSH_accept() clears only want-read/want-write/auth-pending, so a
+     * WS_BAD_ARGUMENT latched by a poll kills the handshake. */
+    int recordError = 0;
+
+    WLOG_ENTER();
+
+    if (ssh == NULL)
+        ret = WS_SSH_NULL_E;
+    else if (ssh->ctx->side != WOLFSSH_ENDPOINT_SERVER) {
+        /* Server side only. wolfSSH_connect() sets ssh->agent too, so the
+         * checks below would report a channel a client never opened. */
+        ret = WS_BAD_ARGUMENT;
+    }
+    else if (SendAfterDisconnect(ssh)) {
+        /* The session is over, so neither a new open nor the flush of one
+         * queued before the disconnect may go out. RFC 4253 section 11.1.
+         * WS_DISCONNECT is in ssh->error, where the rest of the API puts
+         * it. */
+        ret = WS_FATAL_ERROR;
+    }
+    else if (!ssh->useAgent) {
+        /* Nothing asked for agent forwarding on this session. */
+        ret = WS_BAD_ARGUMENT;
+    }
+    else if (ssh->agent == NULL) {
+        /* Nothing else sets ssh->agent, so a NULL one means "not opened
+         * yet". Idempotent, so a poll cannot open a second channel. */
+        WLOG(WS_LOG_AGENT, "Starting agent channel");
+
+        newAgent = wolfSSH_AGENT_new(ssh->ctx->heap);
+        if (newAgent == NULL)
+            ret = WS_MEMORY_E;
+
+        if (ret == WS_SUCCESS) {
+            newChannel = ChannelNew(ssh, ID_CHANTYPE_AUTH_AGENT,
+                    ssh->ctx->windowSz, ssh->ctx->maxPacketSz);
+            if (newChannel == NULL)
+                ret = WS_MEMORY_E;
+        }
+
+        if (ret == WS_SUCCESS) {
+            recordError = 1;
+            ret = SendChannelOpenSession(ssh, newChannel);
+
+            if (ret < WS_SUCCESS
+                    && ret != WS_WANT_WRITE && ret != WS_WANT_READ) {
+                ChannelDelete(newChannel, ssh->ctx->heap);
+            }
+            else {
+                /* Publish on a queued open too, so a retry takes the
+                 * already-open path rather than opening a second. */
+                ChannelAppend(ssh, newChannel);
+                newAgent->channel = newChannel->channel;
+                ssh->agent = newAgent;
+                newAgent = NULL;
+                if (ssh->ctx->agentCb) {
+                    ssh->ctx->agentCb(WOLFSSH_AGENT_LOCAL_SETUP,
+                            ssh->agentCbCtx);
+                }
+            }
+        }
+
+        if (newAgent != NULL)
+            wolfSSH_AGENT_free(newAgent);
+    }
+    else if (wolfSSH_OutputPending(ssh)) {
+        /* Any queued output, not just this open. Flush it rather than
+         * report a success the peer hasn't seen. */
+        recordError = 1;
+        ret = wolfSSH_SendPacket(ssh);
+    }
+
+    if (recordError)
+        ssh->error = ret;
+
+    WLOG_LEAVE(ret);
+    return ret;
+}
+
+
 int wolfSSH_AGENT_worker(WOLFSSH* ssh)
 {
     int ret = WS_SUCCESS;

src/internal.c

@@ -1672,6 +1672,7 @@ WOLFSSH* SshInit(WOLFSSH* ssh, WOLFSSH_CTX* ctx)
     ssh->highwaterMark = ctx->highwaterMark;
     ssh->msgHighwaterMark = ctx->msgHighwaterMark;
     ssh->maxAuthAttempts = ctx->maxAuthAttempts;
+    ssh->appChannels = ctx->appChannels;
     ssh->highwaterCtx  = (void*)ssh;
     ssh->reqSuccessCtx = (void*)ssh;
     ssh->fs            = NULL;
@@ -11799,6 +11800,56 @@ static int DoGlobalRequestFwd(WOLFSSH* ssh,
 }
 #endif
 
+/* Puts a global request to the generic callback, which sees the name and
+ * the type-specific part to parse itself. Returns 1 when the callback
+ * settled the request, with any wanted reply sent and *ret carrying the
+ * result, or 0 to leave it to the built-in handling. */
+static int DoGlobalRequestAny(WOLFSSH* ssh, const char* name, int globReqId,
+        byte* buf, word32 len, word32 begin, byte wantReply, int* ret)
+{
+    int decision, success;
+
+    if (ssh->ctx->globalReqAnyCb == NULL) {
+        return 0;
+    }
+
+    decision = ssh->ctx->globalReqAnyCb(ssh, name, buf + begin, len - begin,
+            wantReply, ssh->globalReqCtx);
+    if (decision != WOLFSSH_REQ_ACCEPT && decision != WOLFSSH_REQ_REJECT) {
+        return 0;
+    }
+    success = (decision == WOLFSSH_REQ_ACCEPT);
+
+#ifdef WOLFSSH_FWD
+    /* RFC 4254 7.1: a port-0 request is answered with the port bound,
+     * which only the forward callback can report. */
+    if (success && globReqId == ID_GLOBREQ_TCPIP_FWD) {
+        const byte* bindAddr;
+        word32 bindAddrSz, bindPort = 0, peek = begin;
+
+        if (GetStringRef(&bindAddrSz, &bindAddr, buf, len, &peek)
+                    != WS_SUCCESS
+                || GetUint32(&bindPort, buf, len, &peek) != WS_SUCCESS
+                || bindPort == 0) {
+            WLOG(WS_LOG_WARN, "DGR: a port-0 forward needs the forward "
+                    "callback to bind it; rejecting");
+            success = 0;
+        }
+    }
+#else
+    (void)globReqId;
+#endif
+
+    WLOG(WS_LOG_DEBUG, "DGR: global request callback %s",
+            success ? "granted" : "refused");
+    if (wantReply) {
+        *ret = SendRequestSuccess(ssh, success);
+    }
+
+    return 1;
+}
+
+
 static int DoGlobalRequest(WOLFSSH* ssh,
                            byte* buf, word32 len, word32* idx)
 {
@@ -11845,31 +11896,37 @@ static int DoGlobalRequest(WOLFSSH* ssh,
         }
         else
 #endif
-        switch (globReqId) {
+        if (!DoGlobalRequestAny(ssh, name, globReqId, buf, len, begin,
+                    wantReply, &ret)) {
+            switch (globReqId) {
 #ifdef WOLFSSH_FWD
-            case ID_GLOBREQ_TCPIP_FWD:
-                ret = DoGlobalRequestFwd(ssh, buf, len, &begin, wantReply, 0);
-                wantReply = 0;
-                break;
-            case ID_GLOBREQ_TCPIP_FWD_CANCEL:
-                ret = DoGlobalRequestFwd(ssh, buf, len, &begin, wantReply, 1);
-                wantReply = 0;
-                break;
+                case ID_GLOBREQ_TCPIP_FWD:
+                    ret = DoGlobalRequestFwd(ssh, buf, len, &begin,
+                            wantReply, 0);
+                    wantReply = 0;
+                    break;
+                case ID_GLOBREQ_TCPIP_FWD_CANCEL:
+                    ret = DoGlobalRequestFwd(ssh, buf, len, &begin,
+                            wantReply, 1);
+                    wantReply = 0;
+                    break;
 #endif
-            default:
-                if (ssh->ctx->globalReqCb != NULL) {
-                    ret = ssh->ctx->globalReqCb(ssh, name, nameSz, wantReply,
-                            (void *)ssh->globalReqCtx);
+                default:
+                    if (ssh->ctx->globalReqCb != NULL) {
+                        ret = ssh->ctx->globalReqCb(ssh, name, nameSz,
+                                wantReply, (void *)ssh->globalReqCtx);
 
-                    if (wantReply) {
-                        ret = SendRequestSuccess(ssh, (ret == WS_SUCCESS));
+                        if (wantReply) {
+                            ret = SendRequestSuccess(ssh,
+                                    (ret == WS_SUCCESS));
+                        }
                     }
-                }
-                else if (wantReply)
-                    ret = SendRequestSuccess(ssh, 0);
-                    /* response SSH_MSG_REQUEST_FAILURE to Keep-Alive.
-                     * IETF:draft-ssh-global-requests */
-                break;
+                    else if (wantReply)
+                        ret = SendRequestSuccess(ssh, 0);
+                        /* response SSH_MSG_REQUEST_FAILURE to Keep-Alive.
+                         * IETF:draft-ssh-global-requests */
+                    break;
+            }
         }
     }
 
@@ -12666,6 +12723,65 @@ static void SetTerminalSize(WOLFSSH* ssh, word32 widthChar, word32 heightRows,
 #endif /* WOLFSSH_TERM */
 
 
+/* Answers a shell, exec, or subsystem request. The session type, and the
+ * command for the two that carry one, are set for the callback to read and
+ * kept only if it accepts; a refused request leaves the channel as it was
+ * and the accept loop still waiting, so nothing serves a session the
+ * application turned down. Without a callback the request is accepted,
+ * unless the application drives its own channels. A request the generic
+ * callback already granted asks no callback. */
+static int DoChannelRequestSession(WOLFSSH* ssh, WOLFSSH_CHANNEL* channel,
+        byte sessionType, WS_CallbackChannelReq cb, int granted,
+        byte* buf, word32 len, word32* idx, int* rej)
+{
+    char* prevCommand = NULL;
+    byte prevType = channel->sessionType;
+    byte hasCommand = (sessionType != WOLFSSH_SESSION_SHELL);
+    int ret = WS_SUCCESS;
+
+    if (hasCommand) {
+        prevCommand = channel->command;
+        channel->command = NULL;
+        ret = GetStringAlloc(ssh->ctx->heap, &channel->command, NULL,
+                buf, len, idx);
+        if (ret == WS_SUCCESS) {
+            WLOG(WS_LOG_DEBUG, "  command = %s", channel->command);
+        }
+    }
+
+    if (ret == WS_SUCCESS) {
+        channel->sessionType = sessionType;
+        if (granted) {
+            *rej = 0;
+        }
+        else if (cb != NULL) {
+            *rej = cb(channel, ssh->channelReqCtx);
+        }
+        else {
+            *rej = ssh->appChannels;
+        }
+    }
+
+    if (ret == WS_SUCCESS && !*rej) {
+        if (prevCommand != NULL) {
+            WFREE(prevCommand, ssh->ctx->heap, DYNTYPE_STRING);
+        }
+        ssh->clientState = CLIENT_DONE;
+    }
+    else {
+        if (hasCommand) {
+            if (channel->command != NULL) {
+                WFREE(channel->command, ssh->ctx->heap, DYNTYPE_STRING);
+            }
+            channel->command = prevCommand;
+        }
+        channel->sessionType = prevType;
+    }
+
+    return ret;
+}
+
+
 static int DoChannelRequest(WOLFSSH* ssh,
                             byte* buf, word32 len, word32* idx)
 {
@@ -12675,7 +12791,7 @@ static int DoChannelRequest(WOLFSSH* ssh,
     word32 typeSz;
     char type[32];
     byte wantReply;
-    int ret, rej = 0;
+    int ret, rej = 0, granted = 0;
 
     WLOG(WS_LOG_DEBUG, "Entering DoChannelRequest()");
 
@@ -12704,6 +12820,23 @@ static int DoChannelRequest(WOLFSSH* ssh,
         WLOG(WS_LOG_DEBUG, "  type = %s", type);
         WLOG(WS_LOG_DEBUG, "  wantReply = %u", wantReply);
 
+        /* The generic callback sees every request first, with the
+         * type-specific part to parse itself. A refusal skips the handling
+         * below; a grant runs it with the decision already made. */
+        if (ssh->ctx->channelReqAnyCb != NULL) {
+            int decision = ssh->ctx->channelReqAnyCb(channel, type,
+                    buf + begin, len - begin, ssh->channelReqCtx);
+            if (decision == WOLFSSH_REQ_REJECT) {
+                WLOG(WS_LOG_DEBUG, "  channel request callback refused.");
+                rej = 1;
+            }
+            else if (decision == WOLFSSH_REQ_ACCEPT) {
+                granted = 1;
+            }
+        }
+    }
+
+    if (ret == WS_SUCCESS && !rej) {
         if (ChannelRequestIs(type, typeSz, "env")) {
             char name[WOLFSSH_MAX_NAMESZ];
             word32 nameSz;
@@ -12721,33 +12854,19 @@ static int DoChannelRequest(WOLFSSH* ssh,
             WLOG(WS_LOG_DEBUG, "  %s = %s", name, value);
         }
         else if (ChannelRequestIs(type, typeSz, "shell")) {
-            channel->sessionType = WOLFSSH_SESSION_SHELL;
-            if (ssh->ctx->channelReqShellCb) {
-                rej = ssh->ctx->channelReqShellCb(channel, ssh->channelReqCtx);
-            }
-            ssh->clientState = CLIENT_DONE;
+            ret = DoChannelRequestSession(ssh, channel, WOLFSSH_SESSION_SHELL,
+                    ssh->ctx->channelReqShellCb, granted, buf, len, &begin,
+                    &rej);
         }
         else if (ChannelRequestIs(type, typeSz, "exec")) {
-            ret = GetStringAlloc(ssh->ctx->heap, &channel->command, NULL,
-                    buf, len, &begin);
-            channel->sessionType = WOLFSSH_SESSION_EXEC;
-            if (ssh->ctx->channelReqExecCb) {
-                rej = ssh->ctx->channelReqExecCb(channel, ssh->channelReqCtx);
-            }
-            ssh->clientState = CLIENT_DONE;
-
-            WLOG(WS_LOG_DEBUG, "  command = %s", channel->command);
+            ret = DoChannelRequestSession(ssh, channel, WOLFSSH_SESSION_EXEC,
+                    ssh->ctx->channelReqExecCb, granted, buf, len, &begin,
+                    &rej);
         }
         else if (ChannelRequestIs(type, typeSz, "subsystem")) {
-            ret = GetStringAlloc(ssh->ctx->heap, &channel->command, NULL,
-                    buf, len, &begin);
-            channel->sessionType = WOLFSSH_SESSION_SUBSYSTEM;
-            if (ssh->ctx->channelReqSubsysCb) {
-                rej = ssh->ctx->channelReqSubsysCb(channel, ssh->channelReqCtx);
-            }
-            ssh->clientState = CLIENT_DONE;
-
-            WLOG(WS_LOG_DEBUG, "  subsystem = %s", channel->command);
+            ret = DoChannelRequestSession(ssh, channel,
+                    WOLFSSH_SESSION_SUBSYSTEM, ssh->ctx->channelReqSubsysCb,
+                    granted, buf, len, &begin, &rej);
         }
         #ifdef WOLFSSH_TERM
         else if (ChannelRequestIs(type, typeSz, "pty-req")) {
@@ -12872,6 +12991,9 @@ static int DoChannelRequest(WOLFSSH* ssh,
                 WLOG(WS_LOG_AGENT, "Agent callback not set, not using.");
         }
         #endif /* WOLFSSH_AGENT */
+        else if (granted) {
+            WLOG(WS_LOG_DEBUG, "  unknown channel request type, granted.");
+        }
         else {
             WLOG(WS_LOG_DEBUG, "  unknown channel request type, rejecting.");
             rej = 1;
@@ -12886,7 +13008,7 @@ static int DoChannelRequest(WOLFSSH* ssh,
         int replyRet;
 
         if (rej) {
-            WLOG(WS_LOG_DEBUG, "Callback rejecting channel request.");
+            WLOG(WS_LOG_DEBUG, "Rejecting channel request.");
         }
         replyRet = SendChannelSuccess(ssh, channelId,
                 (ret == WS_SUCCESS && !rej));