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[Libguestfs] [PATCH 1/2] generator: Add 'Key' parameter type.



-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://et.redhat.com/~rjones/virt-df/
>From 581a7965faa5bf242ab3f8b7c259ab17c2e967f4 Mon Sep 17 00:00:00 2001
From: Richard Jones <rjones redhat com>
Date: Wed, 21 Jul 2010 12:52:51 +0100
Subject: [PATCH 1/2] generator: Add 'Key' parameter type.

Add a 'Key' parameter type, used for passing sensitive key material
into libguestfs.

Eventually the plan is to mlock() key material into memory.  However
this is very difficult to achieve because the encoded XDR strings
end up in many places.  Therefore users should note that key material
passed to libguestfs might end up in swap.

The only difference between 'Key' and 'String' currently is that
guestfish requests the key from /dev/tty with echoing turned off.
---
 fish/fish.c        |   67 +++++++++++++++++
 fish/fish.h        |    1 +
 fish/guestfish.pod |    5 ++
 src/generator.ml   |  202 ++++++++++++++++++++++++++++++++-------------------
 src/guestfs.pod    |   15 ++++
 5 files changed, 215 insertions(+), 75 deletions(-)

diff --git a/fish/fish.c b/fish/fish.c
index 4276ae1..68f26ed 100644
--- a/fish/fish.c
+++ b/fish/fish.c
@@ -29,6 +29,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <locale.h>
+#include <termios.h>
 
 #ifdef HAVE_LIBREADLINE
 #include <readline/readline.h>
@@ -80,6 +81,7 @@ int remote_control_listen = 0;
 int remote_control = 0;
 int exit_on_error = 1;
 int command_num = 0;
+int keys_from_stdin = 0;
 
 static void __attribute__((noreturn))
 usage (int status)
@@ -110,6 +112,7 @@ usage (int status)
              "  -D|--no-dest-paths   Don't tab-complete paths from guest fs\n"
              "  -f|--file file       Read commands from file\n"
              "  -i|--inspector       Run virt-inspector to get disk mountpoints\n"
+             "  --keys-from-stdin    Read passphrases from stdin\n"
              "  --listen             Listen for remote commands\n"
              "  -m|--mount dev[:mnt] Mount dev on mnt (if omitted, /)\n"
              "  -n|--no-sync         Don't autosync\n"
@@ -149,6 +152,7 @@ main (int argc, char *argv[])
     { "file", 1, 0, 'f' },
     { "help", 0, 0, HELP_OPTION },
     { "inspector", 0, 0, 'i' },
+    { "keys-from-stdin", 0, 0, 0 },
     { "listen", 0, 0, 0 },
     { "mount", 1, 0, 'm' },
     { "new", 1, 0, 'N' },
@@ -239,6 +243,8 @@ main (int argc, char *argv[])
         }
       } else if (STREQ (long_options[option_index].name, "selinux")) {
         guestfs_set_selinux (g, 1);
+      } else if (STREQ (long_options[option_index].name, "keys-from-stdin")) {
+        keys_from_stdin = 1;
       } else {
         fprintf (stderr, _("%s: unknown long option: %s (%d)\n"),
                  program_name, long_options[option_index].name, option_index);
@@ -1710,6 +1716,67 @@ file_out (const char *arg)
   return ret;
 }
 
+/* Read a passphrase ('Key') from /dev/tty with echo off.
+ * The caller (cmds.c) will call free on the string afterwards.
+ * Based on the code in cryptsetup file lib/utils.c.
+ */
+char *
+read_key (const char *param)
+{
+  FILE *infp, *outfp;
+  struct termios orig, temp;
+  char *ret = NULL;
+
+  /* Read and write to /dev/tty if available. */
+  if (keys_from_stdin ||
+      (infp = outfp = fopen ("/dev/tty", "w+")) == NULL) {
+    infp = stdin;
+    outfp = stdout;
+  }
+
+  /* Print the prompt and set no echo. */
+  int tty = isatty (fileno (infp));
+  int tcset = 0;
+  if (tty) {
+    fprintf (outfp, _("Enter key or passphrase (\"%s\"): "), param);
+
+    if (tcgetattr (fileno (infp), &orig) == -1) {
+      perror ("tcgetattr");
+      goto error;
+    }
+    memcpy (&temp, &orig, sizeof temp);
+    temp.c_lflag &= ~ECHO;
+
+    tcsetattr (fileno (infp), TCSAFLUSH, &temp);
+    tcset = 1;
+  }
+
+  size_t n = 0;
+  ssize_t len;
+  len = getline (&ret, &n, infp);
+  if (len == -1) {
+    perror ("getline");
+    ret = NULL;
+    goto error;
+  }
+
+  /* Remove the terminating \n if there is one. */
+  if (len > 0 && ret[len-1] == '\n')
+    ret[len-1] = '\0';
+
+ error:
+  /* Restore echo, close file descriptor. */
+  if (tty && tcset) {
+    printf ("\n");
+    tcsetattr (fileno (infp), TCSAFLUSH, &orig);
+  }
+
+  if (infp != stdin)
+    fclose (infp); /* outfp == infp, so this is closed also */
+
+  return ret;
+}
+
 static void
 print_shell_quote (FILE *stream, const char *str)
 {
diff --git a/fish/fish.h b/fish/fish.h
index 9f64979..da1b087 100644
--- a/fish/fish.h
+++ b/fish/fish.h
@@ -68,6 +68,7 @@ extern char *file_in (const char *arg);
 extern void free_file_in (char *s);
 extern char *file_out (const char *arg);
 extern void extended_help_message (void);
+extern char *read_key (const char *param);
 
 /* in cmds.c (auto-generated) */
 extern void list_commands (void);
diff --git a/fish/guestfish.pod b/fish/guestfish.pod
index 5737c46..86dcf58 100644
--- a/fish/guestfish.pod
+++ b/fish/guestfish.pod
@@ -179,6 +179,11 @@ I<--ro> might not behave correctly.
 
 See also: L<virt-inspector(1)>.
 
+=item B<--keys-from-stdin>
+
+Read key or passphrase parameters from stdin.  The default is
+to try to read passphrases from the user by opening C</dev/tty>.
+
 =item B<--listen>
 
 Fork into the background and listen for remote commands.  See section
diff --git a/src/generator.ml b/src/generator.ml
index 2fb3f48..0df77a3 100755
--- a/src/generator.ml
+++ b/src/generator.ml
@@ -174,6 +174,14 @@ and argt =
      * To return an arbitrary buffer, use RBufferOut.
      *)
   | BufferIn of string
+    (* Key material / passphrase.  Eventually we should treat this
+     * as sensitive and mlock it into physical RAM.  However this
+     * is highly complex because of all the places that XDR-encoded
+     * strings can end up.  So currently the only difference from
+     * 'String' is the way that guestfish requests these parameters
+     * from the user.
+     *)
+  | Key of string
 
 type flags =
   | ProtocolLimitWarning  (* display warning about protocol size limits *)
@@ -5294,7 +5302,7 @@ let map_chars f str =
 let name_of_argt = function
   | Pathname n | Device n | Dev_or_Path n | String n | OptString n
   | StringList n | DeviceList n | Bool n | Int n | Int64 n
-  | FileIn n | FileOut n | BufferIn n -> n
+  | FileIn n | FileOut n | BufferIn n | Key n -> n
 
 let java_name_of_struct typ =
   try List.assoc typ java_structs
@@ -5655,6 +5663,10 @@ I<The caller must free the returned buffer after use>.\n\n"
           pr "%s\n\n" protocol_limit_warning;
         if List.mem DangerWillRobinson flags then
           pr "%s\n\n" danger_will_robinson;
+        if List.exists (function Key _ -> true | _ -> false) (snd style) then
+          pr "This function takes a key or passphrase parameter which
+could contain sensitive material.  Read the section
+L</KEYS AND PASSPHRASES> for more information.\n\n";
         match deprecation_notice flags with
         | None -> ()
         | Some txt -> pr "%s\n\n" txt
@@ -5760,7 +5772,7 @@ and generate_xdr () =
            pr "struct %s_args {\n" name;
            List.iter (
              function
-             | Pathname n | Device n | Dev_or_Path n | String n ->
+             | Pathname n | Device n | Dev_or_Path n | String n | Key n ->
                  pr "  string %s<>;\n" n
              | OptString n -> pr "  str *%s;\n" n
              | StringList n | DeviceList n -> pr "  str %s<>;\n" n
@@ -6046,7 +6058,8 @@ check_state (guestfs_h *g, const char *caller)
       | FileOut n
       | BufferIn n
       | StringList n
-      | DeviceList n ->
+      | DeviceList n
+      | Key n ->
           pr "  if (%s == NULL) {\n" n;
           pr "    error (g, \"%%s: %%s: parameter cannot be NULL\",\n";
           pr "           \"%s\", \"%s\");\n" shortname n;
@@ -6088,7 +6101,8 @@ check_state (guestfs_h *g, const char *caller)
       | Dev_or_Path n
       | FileIn n
       | FileOut n
-      | BufferIn n ->
+      | BufferIn n
+      | Key n ->
           (* guestfish doesn't support string escaping, so neither do we *)
           pr "    printf (\" \\\"%%s\\\"\", %s);\n" n
       | OptString n ->			(* string option *)
@@ -6181,7 +6195,7 @@ check_state (guestfs_h *g, const char *caller)
        | args ->
            List.iter (
              function
-             | Pathname n | Device n | Dev_or_Path n | String n ->
+             | Pathname n | Device n | Dev_or_Path n | String n | Key n ->
                  pr "  args.%s = (char *) %s;\n" n n
              | OptString n ->
                  pr "  args.%s = %s ? (char **) &%s : NULL;\n" n n n
@@ -6461,7 +6475,8 @@ and generate_daemon_actions () =
              function
              | Device n | Dev_or_Path n
              | Pathname n
-             | String n -> ()
+             | String n
+             | Key n -> ()
              | OptString n -> pr "  char *%s;\n" n
              | StringList n | DeviceList n -> pr "  char **%s;\n" n
              | Bool n -> pr "  int %s;\n" n
@@ -6518,7 +6533,7 @@ and generate_daemon_actions () =
                  pr_args n;
                  pr "  REQUIRE_ROOT_OR_RESOLVE_DEVICE (%s, %s, goto done);\n"
                    n (if is_filein then "cancel_receive ()" else "0");
-             | String n -> pr_args n
+             | String n | Key n -> pr_args n
              | OptString n -> pr "  %s = args.%s ? *args.%s : NULL;\n" n n n
              | StringList n ->
                  pr_list_handling_code n;
@@ -7533,7 +7548,8 @@ and generate_test_command_call ?(expect_error = false) ?test test_name cmd =
         | Device n, arg
         | Dev_or_Path n, arg
         | String n, arg
-        | OptString n, arg ->
+        | OptString n, arg
+        | Key n, arg ->
             pr "    const char *%s = \"%s\";\n" n (c_quote arg);
         | BufferIn n, arg ->
             pr "    const char *%s = \"%s\";\n" n (c_quote arg);
@@ -7588,7 +7604,8 @@ and generate_test_command_call ?(expect_error = false) ?test test_name cmd =
         | Pathname n, _
         | Device n, _ | Dev_or_Path n, _
         | String n, _
-        | OptString n, _ ->
+        | OptString n, _
+        | Key n, _ ->
             pr ", %s" n
         | BufferIn n, _ ->
             pr ", %s, %s_size" n n
@@ -7714,6 +7731,7 @@ and generate_fish_cmds () =
         match snd style with
         | [] -> name2
         | args ->
+            let args = List.filter (function Key _ -> false | _ -> true) args in
             sprintf "%s %s"
               name2 (String.concat " " (List.map name_of_argt args)) in
 
@@ -7879,7 +7897,8 @@ and generate_fish_cmds () =
         | Pathname n
         | Dev_or_Path n
         | FileIn n
-        | FileOut n -> pr "  char *%s;\n" n
+        | FileOut n
+        | Key n -> pr "  char *%s;\n" n
         | BufferIn n ->
             pr "  const char *%s;\n" n;
             pr "  size_t %s_size;\n" n
@@ -7890,7 +7909,10 @@ and generate_fish_cmds () =
       ) (snd style);
 
       (* Check and convert parameters. *)
-      let argc_expected = List.length (snd style) in
+      let argc_expected =
+        let args_no_keys =
+          List.filter (function Key _ -> false | _ -> true) (snd style) in
+        List.length args_no_keys in
       pr "  if (argc != %d) {\n" argc_expected;
       pr "    fprintf (stderr, _(\"%%s should have %%d parameter(s)\\n\"), cmd, %d);\n"
         argc_expected;
@@ -7898,12 +7920,12 @@ and generate_fish_cmds () =
       pr "    return -1;\n";
       pr "  }\n";
 
-      let parse_integer fn fntyp rtyp range name i =
+      let parse_integer fn fntyp rtyp range name =
         pr "  {\n";
         pr "    strtol_error xerr;\n";
         pr "    %s r;\n" fntyp;
         pr "\n";
-        pr "    xerr = %s (argv[%d], NULL, 0, &r, xstrtol_suffixes);\n" fn i;
+        pr "    xerr = %s (argv[i++], NULL, 0, &r, xstrtol_suffixes);\n" fn;
         pr "    if (xerr != LONGINT_OK) {\n";
         pr "      fprintf (stderr,\n";
         pr "               _(\"%%s: %%s: invalid integer parameter (%%s returned %%d)\\n\"),\n";
@@ -7925,43 +7947,49 @@ and generate_fish_cmds () =
         pr "  }\n";
       in
 
-      iteri (
-        fun i ->
-          function
-          | Device name
-          | String name ->
-              pr "  %s = argv[%d];\n" name i
-          | Pathname name
-          | Dev_or_Path name ->
-              pr "  %s = resolve_win_path (argv[%d]);\n" name i;
-              pr "  if (%s == NULL) return -1;\n" name
-          | OptString name ->
-              pr "  %s = STRNEQ (argv[%d], \"\") ? argv[%d] : NULL;\n"
-                name i i
-          | BufferIn name ->
-              pr "  %s = argv[%d];\n" name i;
-              pr "  %s_size = strlen (argv[%d]);\n" name i
-          | FileIn name ->
-              pr "  %s = file_in (argv[%d]);\n" name i;
-              pr "  if (%s == NULL) return -1;\n" name
-          | FileOut name ->
-              pr "  %s = file_out (argv[%d]);\n" name i;
-              pr "  if (%s == NULL) return -1;\n" name
-          | StringList name | DeviceList name ->
-              pr "  %s = parse_string_list (argv[%d]);\n" name i;
-              pr "  if (%s == NULL) return -1;\n" name;
-          | Bool name ->
-              pr "  %s = is_true (argv[%d]) ? 1 : 0;\n" name i
-          | Int name ->
-              let range =
-                let min = "(-(2LL<<30))"
-                and max = "((2LL<<30)-1)"
-                and comment =
-                  "The Int type in the generator is a signed 31 bit int." in
-                Some (min, max, comment) in
-              parse_integer "xstrtoll" "long long" "int" range name i
-          | Int64 name ->
-              parse_integer "xstrtoll" "long long" "int64_t" None name i
+      if snd style <> [] then
+        pr "  size_t i = 0;\n";
+
+      List.iter (
+        function
+        | Device name
+        | String name ->
+            pr "  %s = argv[i++];\n" name
+        | Pathname name
+        | Dev_or_Path name ->
+            pr "  %s = resolve_win_path (argv[i++]);\n" name;
+            pr "  if (%s == NULL) return -1;\n" name
+        | OptString name ->
+            pr "  %s = STRNEQ (argv[i], \"\") ? argv[i] : NULL;\n" name;
+            pr "  i++;\n"
+        | BufferIn name ->
+            pr "  %s = argv[i];\n" name;
+            pr "  %s_size = strlen (argv[i]);\n" name;
+            pr "  i++;\n"
+        | FileIn name ->
+            pr "  %s = file_in (argv[i++]);\n" name;
+            pr "  if (%s == NULL) return -1;\n" name
+        | FileOut name ->
+            pr "  %s = file_out (argv[i++]);\n" name;
+            pr "  if (%s == NULL) return -1;\n" name
+        | StringList name | DeviceList name ->
+            pr "  %s = parse_string_list (argv[i++]);\n" name;
+            pr "  if (%s == NULL) return -1;\n" name
+        | Key name ->
+            pr "  %s = read_key (\"%s\");\n" name name;
+            pr "  if (%s == NULL) return -1;\n" name
+        | Bool name ->
+            pr "  %s = is_true (argv[i++]) ? 1 : 0;\n" name
+        | Int name ->
+            let range =
+              let min = "(-(2LL<<30))"
+              and max = "((2LL<<30)-1)"
+              and comment =
+                "The Int type in the generator is a signed 31 bit int." in
+              Some (min, max, comment) in
+            parse_integer "xstrtoll" "long long" "int" range name
+        | Int64 name ->
+            parse_integer "xstrtoll" "long long" "int64_t" None name
       ) (snd style);
 
       (* Call C API function. *)
@@ -7975,7 +8003,8 @@ and generate_fish_cmds () =
         | OptString _ | Bool _
         | Int _ | Int64 _
         | BufferIn _ -> ()
-        | Pathname name | Dev_or_Path name | FileOut name ->
+        | Pathname name | Dev_or_Path name | FileOut name
+        | Key name ->
             pr "  free (%s);\n" name
         | FileIn name ->
             pr "  free_file_in (%s);\n" name
@@ -8228,7 +8257,8 @@ and generate_fish_actions_pod () =
       pr " %s" name;
       List.iter (
         function
-        | Pathname n | Device n | Dev_or_Path n | String n -> pr " %s" n
+        | Pathname n | Device n | Dev_or_Path n | String n ->
+            pr " %s" n
         | OptString n -> pr " %s" n
         | StringList n | DeviceList n -> pr " '%s ...'" n
         | Bool _ -> pr " true|false"
@@ -8236,6 +8266,7 @@ and generate_fish_actions_pod () =
         | Int64 n -> pr " %s" n
         | FileIn n | FileOut n -> pr " (%s|-)" n
         | BufferIn n -> pr " %s" n
+        | Key _ -> () (* keys are entered at a prompt *)
       ) (snd style);
       pr "\n";
       pr "\n";
@@ -8245,6 +8276,10 @@ and generate_fish_actions_pod () =
                       | _ -> false) (snd style) then
         pr "Use C<-> instead of a filename to read/write from stdin/stdout.\n\n";
 
+      if List.exists (function Key _ -> true | _ -> false) (snd style) then
+        pr "This command has one or more key or passphrase parameters.
+Guestfish will prompt for these separately.\n\n";
+
       if List.mem ProtocolLimitWarning flags then
         pr "%s\n\n" protocol_limit_warning;
 
@@ -8299,7 +8334,8 @@ and generate_prototype ?(extern = true) ?(static = false) ?(semicolon = true)
       | Pathname n
       | Device n | Dev_or_Path n
       | String n
-      | OptString n ->
+      | OptString n
+      | Key n ->
           next ();
           pr "const char *%s" n
       | StringList n | DeviceList n ->
@@ -8608,7 +8644,8 @@ copy_table (char * const * argv)
         | Device n | Dev_or_Path n
         | String n
         | FileIn n
-        | FileOut n ->
+        | FileOut n
+        | Key n ->
             (* Copy strings in case the GC moves them: RHBZ#604691 *)
             pr "  char *%s = guestfs_safe_strdup (g, String_val (%sv));\n" n n
         | OptString n ->
@@ -8664,7 +8701,7 @@ copy_table (char * const * argv)
       List.iter (
         function
         | Pathname n | Device n | Dev_or_Path n | String n | OptString n
-        | FileIn n | FileOut n | BufferIn n ->
+        | FileIn n | FileOut n | BufferIn n | Key n ->
             pr "  free (%s);\n" n
         | StringList n | DeviceList n ->
             pr "  ocaml_guestfs_free_strings (%s);\n" n;
@@ -8755,7 +8792,7 @@ and generate_ocaml_prototype ?(is_external = false) name style =
   List.iter (
     function
     | Pathname _ | Device _ | Dev_or_Path _ | String _ | FileIn _ | FileOut _
-    | BufferIn _ -> pr "string -> "
+    | BufferIn _ | Key _ -> pr "string -> "
     | OptString _ -> pr "string option -> "
     | StringList _ | DeviceList _ -> pr "string array -> "
     | Bool _ -> pr "bool -> "
@@ -8924,7 +8961,7 @@ close (g)
         fun i ->
           function
           | Pathname n | Device n | Dev_or_Path n | String n
-          | FileIn n | FileOut n ->
+          | FileIn n | FileOut n | Key n ->
               pr "      char *%s;\n" n
           | BufferIn n ->
               pr "      char *%s;\n" n;
@@ -8947,7 +8984,7 @@ close (g)
           | Pathname _ | Device _ | Dev_or_Path _ | String _ | OptString _
           | Bool _ | Int _ | Int64 _
           | FileIn _ | FileOut _
-          | BufferIn _ -> ()
+          | BufferIn _ | Key _ -> ()
           | StringList n | DeviceList n -> pr "      free (%s);\n" n
         ) (snd style)
       in
@@ -9343,7 +9380,7 @@ and generate_perl_prototype name style =
       match arg with
       | Pathname n | Device n | Dev_or_Path n | String n
       | OptString n | Bool n | Int n | Int64 n | FileIn n | FileOut n
-      | BufferIn n ->
+      | BufferIn n | Key n ->
           pr "$%s" n
       | StringList n | DeviceList n ->
           pr "\\ %s" n
@@ -9614,7 +9651,7 @@ py_guestfs_close (PyObject *self, PyObject *args)
 
       List.iter (
         function
-        | Pathname n | Device n | Dev_or_Path n | String n
+        | Pathname n | Device n | Dev_or_Path n | String n | Key n
         | FileIn n | FileOut n ->
             pr "  const char *%s;\n" n
         | OptString n -> pr "  const char *%s;\n" n
@@ -9635,7 +9672,8 @@ py_guestfs_close (PyObject *self, PyObject *args)
       pr "  if (!PyArg_ParseTuple (args, (char *) \"O";
       List.iter (
         function
-        | Pathname _ | Device _ | Dev_or_Path _ | String _ | FileIn _ | FileOut _ -> pr "s"
+        | Pathname _ | Device _ | Dev_or_Path _ | String _ | Key _
+        | FileIn _ | FileOut _ -> pr "s"
         | OptString _ -> pr "z"
         | StringList _ | DeviceList _ -> pr "O"
         | Bool _ -> pr "i" (* XXX Python has booleans? *)
@@ -9649,7 +9687,8 @@ py_guestfs_close (PyObject *self, PyObject *args)
       pr "                         &py_g";
       List.iter (
         function
-        | Pathname n | Device n | Dev_or_Path n | String n | FileIn n | FileOut n -> pr ", &%s" n
+        | Pathname n | Device n | Dev_or_Path n | String n | Key n
+        | FileIn n | FileOut n -> pr ", &%s" n
         | OptString n -> pr ", &%s" n
         | StringList n | DeviceList n -> pr ", &py_%s" n
         | Bool n -> pr ", &%s" n
@@ -9664,7 +9703,7 @@ py_guestfs_close (PyObject *self, PyObject *args)
       pr "  g = get_handle (py_g);\n";
       List.iter (
         function
-        | Pathname _ | Device _ | Dev_or_Path _ | String _
+        | Pathname _ | Device _ | Dev_or_Path _ | String _ | Key _
         | FileIn _ | FileOut _ | OptString _ | Bool _ | Int _ | Int64 _
         | BufferIn _ -> ()
         | StringList n | DeviceList n ->
@@ -9680,7 +9719,7 @@ py_guestfs_close (PyObject *self, PyObject *args)
 
       List.iter (
         function
-        | Pathname _ | Device _ | Dev_or_Path _ | String _
+        | Pathname _ | Device _ | Dev_or_Path _ | String _ | Key _
         | FileIn _ | FileOut _ | OptString _ | Bool _ | Int _ | Int64 _
         | BufferIn _ -> ()
         | StringList n | DeviceList n ->
@@ -9987,7 +10026,8 @@ static VALUE ruby_guestfs_close (VALUE gv)
 
       List.iter (
         function
-        | Pathname n | Device n | Dev_or_Path n | String n | FileIn n | FileOut n ->
+        | Pathname n | Device n | Dev_or_Path n | String n | Key n
+        | FileIn n | FileOut n ->
             pr "  Check_Type (%sv, T_STRING);\n" n;
             pr "  const char *%s = StringValueCStr (%sv);\n" n n;
             pr "  if (!%s)\n" n;
@@ -10048,7 +10088,7 @@ static VALUE ruby_guestfs_close (VALUE gv)
 
       List.iter (
         function
-        | Pathname _ | Device _ | Dev_or_Path _ | String _
+        | Pathname _ | Device _ | Dev_or_Path _ | String _ | Key _
         | FileIn _ | FileOut _ | OptString _ | Bool _ | Int _ | Int64 _
         | BufferIn _ -> ()
         | StringList n | DeviceList n ->
@@ -10365,7 +10405,8 @@ and generate_java_prototype ?(public=false) ?(privat=false) ?(native=false)
       | String n
       | OptString n
       | FileIn n
-      | FileOut n ->
+      | FileOut n
+      | Key n ->
           pr "String %s" n
       | BufferIn n ->
           pr "byte[] %s" n
@@ -10488,7 +10529,8 @@ Java_com_redhat_et_libguestfs_GuestFS__1close
         | String n
         | OptString n
         | FileIn n
-        | FileOut n ->
+        | FileOut n
+        | Key n ->
             pr ", jstring j%s" n
         | BufferIn n ->
             pr ", jbyteArray j%s" n
@@ -10545,7 +10587,8 @@ Java_com_redhat_et_libguestfs_GuestFS__1close
         | String n
         | OptString n
         | FileIn n
-        | FileOut n ->
+        | FileOut n
+        | Key n ->
             pr "  const char *%s;\n" n
         | BufferIn n ->
             pr "  jbyte *%s;\n" n;
@@ -10582,7 +10625,8 @@ Java_com_redhat_et_libguestfs_GuestFS__1close
         | Device n | Dev_or_Path n
         | String n
         | FileIn n
-        | FileOut n ->
+        | FileOut n
+        | Key n ->
             pr "  %s = (*env)->GetStringUTFChars (env, j%s, NULL);\n" n n
         | OptString n ->
             (* This is completely undocumented, but Java null becomes
@@ -10619,7 +10663,8 @@ Java_com_redhat_et_libguestfs_GuestFS__1close
         | Device n | Dev_or_Path n
         | String n
         | FileIn n
-        | FileOut n ->
+        | FileOut n
+        | Key n ->
             pr "  (*env)->ReleaseStringUTFChars (env, j%s, %s);\n" n n
         | OptString n ->
             pr "  if (j%s)\n" n;
@@ -10900,7 +10945,7 @@ last_error h = do
           function
           | FileIn n
           | FileOut n
-          | Pathname n | Device n | Dev_or_Path n | String n ->
+          | Pathname n | Device n | Dev_or_Path n | String n | Key n ->
               pr "withCString %s $ \\%s -> " n n
           | BufferIn n ->
               pr "withCStringLen %s $ \\(%s, %s_size) -> " n n n
@@ -10916,7 +10961,10 @@ last_error h = do
             | Int n -> sprintf "(fromIntegral %s)" n
             | Int64 n -> sprintf "(fromIntegral %s)" n
             | FileIn n | FileOut n
-            | Pathname n | Device n | Dev_or_Path n | String n | OptString n | StringList n | DeviceList n -> n
+            | Pathname n | Device n | Dev_or_Path n
+            | String n | OptString n
+            | StringList n | DeviceList n
+            | Key n -> n
             | BufferIn n -> sprintf "%s (fromIntegral %s_size)" n n
           ) (snd style) in
         pr "withForeignPtr h (\\p -> c_%s %s)\n" name
@@ -10967,7 +11015,8 @@ and generate_haskell_prototype ~handle ?(hs = false) style =
   List.iter (
     fun arg ->
       (match arg with
-       | Pathname _ | Device _ | Dev_or_Path _ | String _ -> pr "%s" string
+       | Pathname _ | Device _ | Dev_or_Path _ | String _ | Key _ ->
+           pr "%s" string
        | BufferIn _ ->
            if hs then pr "String"
            else pr "CString -> CInt"
@@ -11161,6 +11210,7 @@ namespace Guestfs
           function
           | Pathname n | Device n | Dev_or_Path n | String n | OptString n
           | FileIn n | FileOut n
+          | Key n
           | BufferIn n ->
               pr ", [In] string %s" n
           | StringList n | DeviceList n ->
@@ -11185,6 +11235,7 @@ namespace Guestfs
           function
           | Pathname n | Device n | Dev_or_Path n | String n | OptString n
           | FileIn n | FileOut n
+          | Key n
           | BufferIn n ->
               next (); pr "string %s" n
           | StringList n | DeviceList n ->
@@ -11289,7 +11340,8 @@ print_strings (char *const *argv)
       | Device n | Dev_or_Path n
       | String n
       | FileIn n
-      | FileOut n -> pr "  printf (\"%%s\\n\", %s);\n" n
+      | FileOut n
+      | Key n -> pr "  printf (\"%%s\\n\", %s);\n" n
       | BufferIn n ->
 	  pr "  {\n";
 	  pr "    size_t i;\n";
diff --git a/src/guestfs.pod b/src/guestfs.pod
index e876016..8e3d07c 100644
--- a/src/guestfs.pod
+++ b/src/guestfs.pod
@@ -675,6 +675,21 @@ L</UPLOADING> and L</DOWNLOADING> document how to do this.
 You might also consider mounting the disk image using our FUSE
 filesystem support (L<guestmount(1)>).
 
+=head2 KEYS AND PASSPHRASES
+
+Certain libguestfs calls take a parameter that contains sensitive key
+material, passed in as a C string.
+
+In the future we would hope to change the libguestfs implementation so
+that keys are L<mlock(2)>-ed into physical RAM, and thus can never end
+up in swap.  However this is I<not> done at the moment, because of the
+complexity of such an implementation.
+
+Therefore you should be aware that any key parameter you pass to
+libguestfs might end up being written out to the swap partition.  If
+this is a concern, scrub the swap partition or don't use libguestfs on
+encrypted devices.
+
 =head1 CONNECTION MANAGEMENT
 
 =head2 guestfs_h *
-- 
1.7.1


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