tests: cover the exec and subsystem req callbacks

Only the shell hook had coverage, so nothing held DoChannelRequest() to
handing the command and session type to the exec and subsystem callbacks
or to answering with what they return.

- assert each callback sees the session type and the command string the
  request carried, and the ctx set on the session
- assert an accepting callback draws CHANNEL_SUCCESS and a rejecting one
  CHANNEL_FAILURE, whether it rejects with a WS_ error or a bare nonzero

Author: ejohnstown

tests/regress.c

@@ -3272,6 +3272,127 @@ static void TestChannelCloseCallbackReturnIgnored(void)
     FreeChannelOpenHarness(&harness);
 }
 
+/* Builds a plaintext SSH_MSG_CHANNEL_REQUEST whose type-specific tail is a
+ * single string, which is the shape of both "exec" and "subsystem". */
+static word32 BuildChannelStringRequestPacket(word32 recipientChannelId,
+        const char* type, byte wantReply, const char* arg,
+        byte* out, word32 outSz)
+{
+    byte payload[128];
+    word32 idx = 0;
+
+    idx = AppendUint32(payload, sizeof(payload), idx, recipientChannelId);
+    idx = AppendString(payload, sizeof(payload), idx, type);
+    idx = AppendByte(payload, sizeof(payload), idx, wantReply);
+    idx = AppendString(payload, sizeof(payload), idx, arg);
+
+    return WrapPacket(MSGID_CHANNEL_REQUEST, payload, idx, out, outSz);
+}
+
+/* What a session request callback saw. */
+static int sessionReqCbCalls;
+static WS_SessionType sessionReqCbType;
+static char sessionReqCbCommand[32];
+static void* sessionReqCbCtx;
+static int sessionReqCbReturn;
+
+static int RecordingSessionReqCb(WOLFSSH_CHANNEL* channel, void* ctx)
+{
+    const char* command;
+
+    sessionReqCbCalls++;
+    sessionReqCbCtx = ctx;
+    sessionReqCbCommand[0] = 0;
+
+    if (channel != NULL) {
+        sessionReqCbType = wolfSSH_ChannelGetSessionType(channel);
+        command = wolfSSH_ChannelGetSessionCommand(channel);
+        if (command != NULL) {
+            WSTRNCPY(sessionReqCbCommand, command,
+                    sizeof(sessionReqCbCommand) - 1);
+            sessionReqCbCommand[sizeof(sessionReqCbCommand) - 1] = 0;
+        }
+    }
+
+    return sessionReqCbReturn;
+}
+
+/* Drives one session request through a fresh harness, with the callback
+ * returning cbReturn, and returns the message id the server answered with. */
+static byte RunSessionRequest(const char* type, const char* arg, int cbReturn,
+        WS_SessionType expectType)
+{
+    ChannelOpenHarness harness;
+    WOLFSSH_CHANNEL* channel;
+    byte in[128];
+    word32 inSz;
+    int cbCtx = 0;
+    byte replyId;
+
+    sessionReqCbCalls = 0;
+    sessionReqCbType = WOLFSSH_SESSION_UNKNOWN;
+    sessionReqCbCommand[0] = 0;
+    sessionReqCbCtx = NULL;
+    sessionReqCbReturn = cbReturn;
+
+    InitChannelOpenHarness(&harness, NULL, 0);
+    if (WSTRCMP(type, "exec") == 0) {
+        AssertIntEQ(wolfSSH_CTX_SetChannelReqExecCb(harness.ctx,
+                    RecordingSessionReqCb), WS_SUCCESS);
+    }
+    else {
+        AssertIntEQ(wolfSSH_CTX_SetChannelReqSubsysCb(harness.ctx,
+                    RecordingSessionReqCb), WS_SUCCESS);
+    }
+    AssertIntEQ(wolfSSH_SetChannelReqCtx(harness.ssh, &cbCtx), WS_SUCCESS);
+
+    channel = SeedUnconfirmedChannel(&harness);
+    AssertIntEQ(ChannelUpdatePeer(channel, 5, 1024, 1024), WS_SUCCESS);
+    channel->openConfirmed = 1;
+
+    inSz = BuildChannelStringRequestPacket(channel->channel, type, 1, arg,
+            in, sizeof(in));
+    RepointHarnessInput(&harness, in, inSz);
+
+    AssertIntEQ(DoReceive(harness.ssh), WS_SUCCESS);
+    AssertIntEQ(harness.io.inOff, harness.io.inSz);
+    AssertIntEQ(sessionReqCbCalls, 1);
+    AssertTrue(sessionReqCbCtx == &cbCtx);
+    AssertIntEQ(sessionReqCbType, expectType);
+    AssertIntEQ(WSTRCMP(sessionReqCbCommand, arg), 0);
+
+    replyId = ParseMsgId(harness.io.out, harness.io.outSz);
+    FreeChannelOpenHarness(&harness);
+
+    return replyId;
+}
+
+/* The exec callback is the only place an application can vet a remote
+ * command, and its return is what decides the reply on the wire.
+ * DoChannelRequest() tests only for nonzero, so a bare 1 rejects the same
+ * as a WS_ error. */
+static void TestChannelReqExecCallbackRuns(void)
+{
+    AssertIntEQ(RunSessionRequest("exec", "ls", WS_SUCCESS,
+                WOLFSSH_SESSION_EXEC), MSGID_CHANNEL_SUCCESS);
+    AssertIntEQ(RunSessionRequest("exec", "ls", WS_BAD_ARGUMENT,
+                WOLFSSH_SESSION_EXEC), MSGID_CHANNEL_FAILURE);
+    AssertIntEQ(RunSessionRequest("exec", "ls", 1,
+                WOLFSSH_SESSION_EXEC), MSGID_CHANNEL_FAILURE);
+}
+
+/* Same contract for the subsystem callback, which is how a server decides
+ * whether to serve SFTP on a channel. */
+static void TestChannelReqSubsysCallbackRuns(void)
+{
+    AssertIntEQ(RunSessionRequest("subsystem", "sftp", WS_SUCCESS,
+                WOLFSSH_SESSION_SUBSYSTEM), MSGID_CHANNEL_SUCCESS);
+    AssertIntEQ(RunSessionRequest("subsystem", "sftp", WS_BAD_ARGUMENT,
+                WOLFSSH_SESSION_SUBSYSTEM), MSGID_CHANNEL_FAILURE);
+    AssertIntEQ(RunSessionRequest("subsystem", "sftp", 1,
+                WOLFSSH_SESSION_SUBSYSTEM), MSGID_CHANNEL_FAILURE);
+}
+
 /* A username change after the first userauth request must end the session. */
 static void TestUsernameChangeDisconnects(void)
 {
@@ -12472,6 +12593,8 @@ int main(int argc, char** argv)
     TestChannelOpenFailCallbackRejects();
     TestChannelCloseCallbackRuns();
     TestChannelCloseCallbackReturnIgnored();
+    TestChannelReqExecCallbackRuns();
+    TestChannelReqSubsysCallbackRuns();
     TestSecondSessionChannelRejected();
     TestUsernameChangeDisconnects();
     TestSameUserRetryAllowed();