gpg,common: Make sure that all fd given are valid.

* common/sysutils.c (gnupg_fd_valid): New function.
* common/sysutils.h (gnupg_fd_valid): New declaration.
* common/logging.c (log_set_file): Use the new function.
* g10/cpr.c (set_status_fd): Likewise.
* g10/gpg.c (main): Likewise.
* g10/keylist.c (read_sessionkey_from_fd): Likewise.
* g10/passphrase.c (set_attrib_fd): Likewise.
* tests/openpgp/Makefile.am (XTESTS): Add the new test.
* tests/openpgp/issue2941.scm: New file.
--

Consider a situation where the user passes "--status-fd 3" but file
descriptor 3 is not open.

During the course of executing the rest of the commands, it's possible
that gpg itself will open some files, and file descriptor 3 will get
allocated.

In this situation, the status information will be appended directly to
whatever file happens to have landed on fd 3 (the trustdb? the
keyring?).

This is a potential data destruction issue for all writable file
descriptor options:

   --status-fd
   --attribute-fd
   --logger-fd

It's also a potential issue for readable file descriptor options, but
the risk is merely weird behavior, and not data corruption:

   --override-session-key-fd
   --passphrase-fd
   --command-fd

Fixes this by checking whether the fd is valid early on before using
it.

GnuPG-bug-id: 2941
Signed-off-by: Justus Winter <justus@g10code.com>

common/logging.c

@@ -570,6 +570,9 @@ log_set_file (const char *name)
 void
 log_set_fd (int fd)
 {
+  if (! gnupg_fd_valid (fd))
+    log_fatal ("logger-fd is invalid: %s\n", strerror (errno));
+
   set_file_fd (NULL, fd);
 }
 

common/sysutils.c

@@ -1281,3 +1281,14 @@ gnupg_get_socket_name (int fd)
   return name;
 }
 #endif /*!HAVE_W32_SYSTEM*/
+
+/* Check whether FD is valid.  */
+int
+gnupg_fd_valid (int fd)
+{
+  int d = dup (fd);
+  if (d < 0)
+    return 0;
+  close (d);
+  return 1;
+}

common/sysutils.h

@@ -72,6 +72,7 @@ int  gnupg_setenv (const char *name, const char *value, int overwrite);
 int  gnupg_unsetenv (const char *name);
 char *gnupg_getcwd (void);
 char *gnupg_get_socket_name (int fd);
+int gnupg_fd_valid (int fd);
 
 gpg_error_t gnupg_inotify_watch_socket (int *r_fd, const char *socket_name);
 int gnupg_inotify_has_name (int fd, const char *name);

g10/cpr.c

@@ -107,6 +107,9 @@ set_status_fd (int fd)
   if (fd == -1)
     return;
 
+  if (! gnupg_fd_valid (fd))
+    log_fatal ("status-fd is invalid: %s\n", strerror (errno));
+
   if (fd == 1)
     statusfp = es_stdout;
   else if (fd == 2)

g10/gpg.c

@@ -3079,6 +3079,8 @@ main (int argc, char **argv)
 
 	  case oCommandFD:
             opt.command_fd = translate_sys2libc_fd_int (pargs.r.ret_int, 0);
+	    if (! gnupg_fd_valid (opt.command_fd))
+	      log_fatal ("command-fd is invalid: %s\n", strerror (errno));
             break;
 	  case oCommandFile:
             opt.command_fd = open_info_file (pargs.r.ret_str, 0, 1);
@@ -5293,6 +5295,9 @@ read_sessionkey_from_fd (int fd)
   int i, len;
   char *line;
 
+  if (! gnupg_fd_valid (fd))
+    log_fatal ("override-session-key-fd is invalid: %s\n", strerror (errno));
+
   for (line = NULL, i = len = 100; ; i++ )
     {
       if (i >= len-1 )

g10/keylist.c

@@ -1900,6 +1900,9 @@ set_attrib_fd (int fd)
   if (fd == -1)
     return;
 
+  if (! gnupg_fd_valid (fd))
+    log_fatal ("attribute-fd is invalid: %s\n", strerror (errno));
+
 #ifdef HAVE_DOSISH_SYSTEM
   setmode (fd, O_BINARY);
 #endif

g10/passphrase.c

@@ -166,6 +166,9 @@ read_passphrase_from_fd( int fd )
   int i, len;
   char *pw;
 
+  if (! gnupg_fd_valid (fd))
+    log_fatal ("passphrase-fd is invalid: %s\n", strerror (errno));
+
   if ( !opt.batch && opt.pinentry_mode != PINENTRY_MODE_LOOPBACK)
     { /* Not used but we have to do a dummy read, so that it won't end
          up at the begin of the message if the quite usual trick to

tests/openpgp/Makefile.am

@@ -97,7 +97,8 @@ XTESTS = \
 	issue2346.scm \
 	issue2417.scm \
 	issue2419.scm \
-	issue2929.scm
+	issue2929.scm \
+	issue2941.scm
 
 # XXX: Currently, one cannot override automake's 'check' target.  As a
 # workaround, we avoid defining 'TESTS', thus automake will not emit

tests/openpgp/issue2941.scm

@@ -0,0 +1,34 @@
+#!/usr/bin/env gpgscm
+
+;; Copyright (C) 2017 g10 Code GmbH
+;;
+;; This file is part of GnuPG.
+;;
+;; GnuPG is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 3 of the License, or
+;; (at your option) any later version.
+;;
+;; GnuPG is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program; if not, see <http://www.gnu.org/licenses/>.
+
+(load (with-path "defs.scm"))
+(setup-legacy-environment)
+
+(define (check-failure options)
+  (let ((command `(,@gpg ,@options)))
+    (catch '()
+	   (call-check command)
+	   (error "Expected an error, but got none when executing" command))))
+
+(for-each-p
+ "Checking invocation with invalid file descriptors (issue2941)."
+ (lambda (option)
+   (check-failure `(,(string-append "--" option "=23") --sign gpg.conf)))
+ '("status-fd" "attribute-fd" "logger-fd"
+   "override-session-key-fd" "passphrase-fd" "command-fd"))