Fix console prompts with redirected log

When openvpn needs to prompt user for a password
(for example, to set management interface password),
the prompt is written to standard error device.

When log is redirected to a file, that prompt is written
to that file and not to the "original" stderr. Moreover, on recent
Insider build (21390.2025) openvpn exits with fatal error

  get_console_input_win32(): unexpected error: No such device or address
  (errno=6)

while attempting to write that prompt.

When redirecting stdout/stderr, we use _dup2() to associate stderr
descriptor with a log file. This call closes file associated
with stderr descriptor, which might explain why it has stopped
working (original stderr is closed and WriteFile() fails) and on
older versions it appears to work "by accident" - not failing
but use redirected stderr instead of original one.

Fix by creating new file descriptor with _dup() for stderr
before redirect and use this descriptor for writing prompts.

While on it, make code a bit more C99-ish by moving variables
declaration from the beginning of the scope to the actual
initialisation.

Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20210625010405.224-1-lstipakov@gmail.com>
URL: https://www.mail-archive.com/search?l=mid&q=20210625010405.224-1-lstipakov@gmail.com
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/src/openvpn/console_builtin.c b/src/openvpn/console_builtin.c
index 9bf36347807a20e28bfd2ff6e77c0a9f08457a08..06b8a77a0f4aebaa42eb05f57f8f59dd2710bd7b 100644 (file)
--- a/src/openvpn/console_builtin.c
+++ b/src/openvpn/console_builtin.c
@@ -62,23 +62,17 @@
 static bool
 get_console_input_win32(const char *prompt, const bool echo, char *input, const int capacity)
 {
-    HANDLE in = INVALID_HANDLE_VALUE;
-    HANDLE err = INVALID_HANDLE_VALUE;
-    DWORD len = 0;
-
     ASSERT(prompt);
     ASSERT(input);
     ASSERT(capacity > 0);
 
     input[0] = '\0';
 
-    in = GetStdHandle(STD_INPUT_HANDLE);
-    err = get_orig_stderr();
-
-    if (in == INVALID_HANDLE_VALUE
-        || err == INVALID_HANDLE_VALUE
+    HANDLE in = GetStdHandle(STD_INPUT_HANDLE);
+    int orig_stderr = get_orig_stderr(); // guaranteed to be always valid
+    if ((in == INVALID_HANDLE_VALUE)
         || win32_service_interrupt(&win32_signal)
-        || !WriteFile(err, prompt, strlen(prompt), &len, NULL))
+        || (_write(orig_stderr, prompt, strlen(prompt)) == -1))
     {
         msg(M_WARN|M_ERRNO, "get_console_input_win32(): unexpected error");
         return false;
@@ -106,6 +100,8 @@ get_console_input_win32(const char *prompt, const bool echo, char *input, const
         }
     }
 
+    DWORD len = 0;
+
     if (is_console)
     {
         winput = malloc(capacity * sizeof(WCHAR));
@@ -128,7 +124,7 @@ get_console_input_win32(const char *prompt, const bool echo, char *input, const
 
     if (!echo)
     {
-        WriteFile(err, "\r\n", 2, &len, NULL);
+        _write(orig_stderr, "\r\n", 2);
     }
     if (is_console)
     {

diff --git a/src/openvpn/error.c b/src/openvpn/error.c
index b94d387c742a9ac527f54f8b31add1b1f773e041..eb82f9c7efb422ca294f7fe1d197030839dba573 100644 (file)
--- a/src/openvpn/error.c
+++ b/src/openvpn/error.c
@@ -491,22 +491,12 @@ close_syslog(void)
 }
 
 #ifdef _WIN32
+static int orig_stderr;
 
-static HANDLE orig_stderr;
-
-HANDLE
-get_orig_stderr(void)
+int get_orig_stderr()
 {
-    if (orig_stderr)
-    {
-        return orig_stderr;
-    }
-    else
-    {
-        return GetStdHandle(STD_ERROR_HANDLE);
-    }
+    return orig_stderr ? orig_stderr : _fileno(stderr);
 }
-
 #endif
 
 void
@@ -550,16 +540,12 @@ redirect_stdout_stderr(const char *file, bool append)
         }
 
         /* save original stderr for password prompts */
-        orig_stderr = GetStdHandle(STD_ERROR_HANDLE);
-
-#if 0 /* seems not be necessary with stdout/stderr redirection below*/
-        /* set up for redirection */
-        if (!SetStdHandle(STD_OUTPUT_HANDLE, log_handle)
-            || !SetStdHandle(STD_ERROR_HANDLE, log_handle))
+        orig_stderr = _dup(_fileno(stderr));
+        if (orig_stderr == -1)
         {
-            msg(M_ERR, "Error: cannot redirect stdout/stderr to --log file: %s", file);
+            msg(M_WARN | M_ERRNO, "Warning: cannot duplicate stderr, password prompts will appear in log file instead of console.");
+            orig_stderr = _fileno(stderr);
         }
-#endif
 
         /* direct stdout/stderr to point to log_handle */
         log_fd = _open_osfhandle((intptr_t)log_handle, _O_TEXT);

diff --git a/src/openvpn/error.h b/src/openvpn/error.h
index f4528ef22777b36b3bff1e479d7cbc5a6d1a7aa7..533354b3c16720366538bccff010e12b1bfba559 100644 (file)
--- a/src/openvpn/error.h
+++ b/src/openvpn/error.h
@@ -256,8 +256,8 @@ void close_syslog(void);
 void redirect_stdout_stderr(const char *file, bool append);
 
 #ifdef _WIN32
-/* get original stderr handle, even if redirected by --log/--log-append */
-HANDLE get_orig_stderr(void);
+/* get original stderr fd, even if redirected by --log/--log-append */
+int get_orig_stderr(void);
 
 #endif