ssh: add a channel session-granted accessor

wolfSSH_ChannelGetSessionGranted() reports whether a shell, exec or
subsystem request on a channel has been answered CHANNEL_SUCCESS, so an
application can tell a second request from the first without reaching
into WOLFSSH_CHANNEL.

- the flag is still clear for the request a session callback is
  answering, so a set flag is an earlier request's grant
- wolfsshd's session callback reads the grant through it

apps/wolfsshd/wolfsshd.c

@@ -544,7 +544,7 @@ static int SessionRequestCb(WOLFSSH_CHANNEL* channel, void* vCtx)
     /* One program start per channel, as RFC 4254 section 6.5 allows. This
      * request's grant is recorded once the callback returns, so a flag
      * already set is an earlier request's. */
-    if (!rej && channel->sessionGranted) {
+    if (!rej && wolfSSH_ChannelGetSessionGranted(channel) == 1) {
         rej = 1;
         reason = "a session is already running on the channel";
     }

src/ssh.c

@@ -5774,6 +5774,17 @@ word32 wolfSSH_ChannelGetSessionCommandSz(const WOLFSSH_CHANNEL* channel)
 }
 
 
+/* returns 1 if a session was granted on the channel, 0 if not, and
+ * negative on failure */
+int wolfSSH_ChannelGetSessionGranted(const WOLFSSH_CHANNEL* channel)
+{
+    if (channel == NULL) {
+        return WS_BAD_ARGUMENT;
+    }
+    return channel->sessionGranted;
+}
+
+
 int wolfSSH_CTX_SetChannelOpenCb(WOLFSSH_CTX* ctx, WS_CallbackChannelOpen cb)
 {
     int ret = WS_SSH_CTX_NULL_E;

tests/regress.c

@@ -5862,6 +5862,37 @@ static void TestAcceptDivertMatchesScpCommandToken(void)
 
 #endif /* WOLFSSH_SCP */
 
+/* The grant an application reads through the public accessor is the one the
+ * channel records: clear while the request that would set it is still being
+ * answered, set once it has been. */
+static void TestChannelGetSessionGrantedAccessor(void)
+{
+    ChannelOpenHarness harness;
+    WOLFSSH_CHANNEL* channel;
+    byte in[128];
+    word32 inSz;
+
+    AssertIntEQ(wolfSSH_ChannelGetSessionGranted(NULL), WS_BAD_ARGUMENT);
+
+    InitChannelOpenHarness(&harness, NULL, 0);
+    channel = SeedUnconfirmedChannel(&harness);
+    AssertIntEQ(ChannelUpdatePeer(channel, 5, 1024, 1024), WS_SUCCESS);
+    channel->openConfirmed = 1;
+    AssertIntEQ(wolfSSH_ChannelGetSessionGranted(channel), 0);
+
+    inSz = BuildChannelStringRequestPacket(channel->channel, "exec", 1,
+            "ls", in, sizeof(in));
+    RepointHarnessInput(&harness, in, inSz);
+
+    AssertIntEQ(DoReceive(harness.ssh), WS_SUCCESS);
+    AssertIntEQ(wolfSSH_ChannelGetSessionGranted(channel), 1);
+    AssertIntEQ(wolfSSH_ChannelGetSessionGranted(channel),
+            channel->sessionGranted);
+
+    FreeChannelOpenHarness(&harness);
+}
+
+
 /* A username change after the first userauth request must end the session. */
 static void TestUsernameChangeDisconnects(void)
 {
@@ -16006,6 +16037,7 @@ int main(int argc, char** argv)
     TestChannelReqExecCallbackRuns();
     TestChannelReqSubsysCallbackRuns();
     TestSessionReqCallbackSeesCommandSz();
+    TestChannelGetSessionGrantedAccessor();
     TestMalformedSessionRequestSkipsCallback();
     TestSessionReqCallbackMayFreeChannel();
     TestAppChannelsAcceptKeepsStopWithPendingOutput();

wolfssh/ssh.h

@@ -451,6 +451,12 @@ WOLFSSH_API const char* wolfSSH_ChannelGetSessionCommand(
 WOLFSSH_API word32 wolfSSH_ChannelGetSessionCommandSz(
         const WOLFSSH_CHANNEL* channel);
 WOLFSSH_API int wolfSSH_ChannelIsPty(const WOLFSSH_CHANNEL* channel);
+/* Returns 1 once a shell, exec or subsystem request on the channel has been
+ * answered CHANNEL_SUCCESS, 0 while none has been, and WS_BAD_ARGUMENT when
+ * channel is NULL. A session-request callback sees this still clear for the
+ * request it is answering, so a set flag is an earlier request's grant. */
+WOLFSSH_API int wolfSSH_ChannelGetSessionGranted(
+        const WOLFSSH_CHANNEL* channel);
 
 /* Channel callbacks */
 typedef int (*WS_CallbackChannelOpen)(WOLFSSH_CHANNEL* channel, void* ctx);