Unbuffer stdin before a client password prompt

The password prompt reads stdin with fgets(), and a buffered stdin
keeps its own copy of the line in libc for the life of the process.
The clients make stdin unbuffered before any stdin I/O, so the typed
password lands only in the buffer ClientUserAuth() wipes.

- the wolfssh app, and the example client, sftp client and scp client
  whether or not -P was given, as keyboard-interactive reads stdin too
- ClientUnbufferStdin() acts once per process and reports a failure
- scripts/sshclient.test sends the session data right after the
  password, with no sleep

Issue: F-15669

apps/wolfssh/wolfssh.c

@@ -1270,6 +1270,9 @@ static THREAD_RETURN WOLFSSH_THREAD wolfSSH_Client(void* args)
 #endif
 
     MODES_STORE();
+    /* No stdio buffer keeps a copy of a typed password. */
+    if (setvbuf(stdin, NULL, _IONBF, 0) != 0)
+        fprintf(stderr, "Couldn't unbuffer stdin.\n");
 
     ((func_args*)args)->return_code = 0;
 

examples/client/client.c

@@ -1006,6 +1006,10 @@ THREAD_RETURN WOLFSSH_THREAD client_test(void* args)
     }
     myoptind = 0;      /* reset for test cases */
 
+#ifdef WOLFSSH_TERM
+    ClientUnbufferStdin();
+#endif
+
     if (username == NULL)
         err_sys("client requires a username parameter.");
 

examples/client/common.c

@@ -675,6 +675,18 @@ void ClientClearPassword(void)
 
 
 #ifdef WOLFSSH_TERM
+void ClientUnbufferStdin(void)
+{
+    static int done = 0;
+
+    if (!done) {
+        done = 1;
+        if (setvbuf(stdin, NULL, _IONBF, 0) != 0)
+            fprintf(stderr, "Couldn't unbuffer stdin.\n");
+    }
+}
+
+
 /* type = 2 : shell / execute command settings
  * type = 0 : password
  * type = 1 : restore default

examples/client/common.h

@@ -32,6 +32,10 @@ int ClientSetPrivateKey(const char* privKeyName, int userEcc,
         void* heap, const char* tpmKeyAuth);
 int ClientUseCert(const char* certName, void* heap);
 int ClientSetEcho(int type);
+/* Makes stdin unbuffered, so no stdio buffer keeps a copy of a typed
+ * password or response. Call before any other stdin I/O; only the first
+ * call in a process acts. */
+void ClientUnbufferStdin(void);
 int ClientUserAuth(byte authType,
         WS_UserAuthData* authData, void* ctx);
 int ClientPublicKeyCheck(const byte* pubKey, word32 pubKeySz, void* ctx);

examples/scpclient/scpclient.c

@@ -193,6 +193,10 @@ THREAD_RETURN WOLFSSH_THREAD scp_client(void* args)
 
     myoptind = 0;      /* reset for test cases */
 
+#ifdef WOLFSSH_TERM
+    ClientUnbufferStdin();
+#endif
+
     if (username == NULL)
         err_sys("client requires a username parameter.");
 

examples/sftpclient/sftpclient.c

@@ -1719,6 +1719,10 @@ THREAD_RETURN WOLFSSH_THREAD sftpclient_test(void* args)
     }
     myoptind = 0;      /* reset for test cases */
 
+#ifdef WOLFSSH_TERM
+    ClientUnbufferStdin();
+#endif
+
     if (username == NULL)
         err_sys("client requires a username parameter.");
 

scripts/sshclient.test

@@ -136,10 +136,9 @@ wait_for_output() {
 
 # Run the client with its stdin coming from a fifo.
 #
-# The client answers its prompts with stdio, which buffers everything that
-# is ready to be read, so anything written along with a prompt's answer is
-# swallowed with it and never reaches the session. Writing each piece only
-# once the client has asked for it keeps them in separate reads. The
+# The client reads its prompt answers from an unbuffered stdin, so the
+# session data can follow the password at once and is left in the fifo for
+# the session. Each answer is still written only once its prompt is up. The
 # echoserver only ends the session when it receives a 0x03, so every
 # session has to send one or both ends wait for the other forever.
 #
@@ -161,11 +160,6 @@ run_client() {
 
         wait_for_output "Password:" || exit 1
         printf 'upthehill\n'
-
-        # Let the client consume the password before sending the session
-        # data. A single read that catches both loses the data.
-        sleep 2
-
         printf 'hello\003'
     ) > "$input_file" 2>/dev/null &
     input_pid=$!