[Qemu-devel] [PATCH v3] qga: add guest-set-user-password command

["Daniel P. Berrange" <berrange@redhat.com>]

Add a new 'guest-set-user-password' command for changing the password
of guest OS user accounts. This command is needed to enable OpenStack
to support its API for changing the admin password of guests running
on KVM/QEMU. It is not practical to provide a command at the QEMU
level explicitly targetting administrator account password change
only, since different guest OS have different names for the admin
account. While UNIX systems use 'root', Windows systems typically
use 'Administrator' and even that can be renamed. Higher level apps
like OpenStack have the ability to figure out the correct admin
account name since they have info that QEMU/libvirt do not.

The command accepts either the clear text password string, encoded
in base64 to make it 8-bit safe in JSON:

$ echo -n "123456" | base64
MTIzNDU2
$ virsh -c qemu:///system  qemu-agent-command f21x86_64 \
   '{ "execute": "guest-set-user-password",
      "arguments": { "crypted": false,
                     "username": "root",
                     "password": "MTIzNDU2" } }'
  {"return":{}}

Or a password that has already been run though a crypt(3) like
algorithm appropriate for the guest, again then base64 encoded:

$ echo -n '$6$n01A2Tau$e...snip...DfMOP7of9AJ1I8q0' | base64
JDYkb...snip...YT2Ey
$ virsh -c qemu:///system  qemu-agent-command f21x86_64 \
   '{ "execute": "guest-set-user-password",
      "arguments": { "crypted": true,
                     "username": "root",
                     "password": "JDYkb...snip...YT2Ey" } }'

NB windows support is desirable, but not implemented in this
patch.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 qga/commands-posix.c | 110 +++++++++++++++++++++++++++++++++++++++++++++++++++
 qga/commands-win32.c |   9 +++++
 qga/qapi-schema.json |  27 +++++++++++++
 3 files changed, 146 insertions(+)

In v3:

 - Renamed from guest-set-admin-password to guest-set-user-password
 - Added 'username' argument
 - Require 'password' to be base64 encoded

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index f6f3e3c..57409d0 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -1875,6 +1875,108 @@ int64_t qmp_guest_set_vcpus(GuestLogicalProcessorList *vcpus, Error **errp)
     return processed;
 }
 
+void qmp_guest_set_user_password(const char *username,
+                                 const char *password,
+                                 bool crypted,
+                                 Error **errp)
+{
+    Error *local_err = NULL;
+    char *passwd_path = NULL;
+    pid_t pid;
+    int status;
+    int datafd[2] = { -1, -1 };
+    char *rawpasswddata = NULL;
+    size_t rawpasswdlen;
+    char *chpasswddata = NULL;
+    size_t chpasswdlen;
+
+    rawpasswddata = (char *)g_base64_decode(password, &rawpasswdlen);
+    rawpasswddata = g_renew(char, rawpasswddata, rawpasswdlen + 1);
+    rawpasswddata[rawpasswdlen] = '\0';
+
+    if (strchr(rawpasswddata, '\n')) {
+        error_setg(errp, "forbidden characters in raw password");
+        goto out;
+    }
+
+    if (strchr(username, '\n') ||
+        strchr(username, ':')) {
+        error_setg(errp, "forbidden characters in username");
+        goto out;
+    }
+
+    chpasswddata = g_strdup_printf("%s:%s\n", username, rawpasswddata);
+    chpasswdlen = strlen(chpasswddata);
+
+    passwd_path = g_find_program_in_path("chpasswd");
+
+    if (!passwd_path) {
+        error_setg(errp, "cannot find 'passwd' program in PATH");
+        goto out;
+    }
+
+    if (pipe(datafd) < 0) {
+        error_setg(errp, "cannot create pipe FDs");
+        goto out;
+    }
+
+    pid = fork();
+    if (pid == 0) {
+        close(datafd[1]);
+        /* child */
+        setsid();
+        dup2(datafd[0], 0);
+        reopen_fd_to_null(1);
+        reopen_fd_to_null(2);
+
+        if (crypted) {
+            execle(passwd_path, "chpasswd", "-e", NULL, environ);
+        } else {
+            execle(passwd_path, "chpasswd", NULL, environ);
+        }
+        _exit(EXIT_FAILURE);
+    } else if (pid < 0) {
+        error_setg_errno(errp, errno, "failed to create child process");
+        goto out;
+    }
+    close(datafd[0]);
+    datafd[0] = -1;
+
+    if (qemu_write_full(datafd[1], chpasswddata, chpasswdlen) != chpasswdlen) {
+        error_setg_errno(errp, errno, "cannot write new account password");
+        goto out;
+    }
+    close(datafd[1]);
+    datafd[1] = -1;
+
+    ga_wait_child(pid, &status, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        goto out;
+    }
+
+    if (!WIFEXITED(status)) {
+        error_setg(errp, "child process has terminated abnormally");
+        goto out;
+    }
+
+    if (WEXITSTATUS(status)) {
+        error_setg(errp, "child process has failed to set user password");
+        goto out;
+    }
+
+out:
+    g_free(chpasswddata);
+    g_free(rawpasswddata);
+    g_free(passwd_path);
+    if (datafd[0] != -1) {
+        close(datafd[0]);
+    }
+    if (datafd[1] != -1) {
+        close(datafd[1]);
+    }
+}
+
 #else /* defined(__linux__) */
 
 void qmp_guest_suspend_disk(Error **errp)
@@ -1910,6 +2012,14 @@ int64_t qmp_guest_set_vcpus(GuestLogicalProcessorList *vcpus, Error **errp)
     return -1;
 }
 
+void qmp_guest_set_user_password(const char *username,
+                                 const char *password,
+                                 bool crypted,
+                                 Error **errp)
+{
+    error_set(errp, QERR_UNSUPPORTED);
+}
+
 #endif
 
 #if !defined(CONFIG_FSFREEZE)
diff --git a/qga/commands-win32.c b/qga/commands-win32.c
index 3bcbeae..11876f6 100644
--- a/qga/commands-win32.c
+++ b/qga/commands-win32.c
@@ -446,6 +446,14 @@ int64_t qmp_guest_set_vcpus(GuestLogicalProcessorList *vcpus, Error **errp)
     return -1;
 }
 
+void qmp_guest_set_user_password(const char *username,
+                                 const char *password,
+                                 bool crypted,
+                                 Error **errp)
+{
+    error_set(errp, QERR_UNSUPPORTED);
+}
+
 /* add unsupported commands to the blacklist */
 GList *ga_command_blacklist_init(GList *blacklist)
 {
@@ -454,6 +462,7 @@ GList *ga_command_blacklist_init(GList *blacklist)
         "guest-file-write", "guest-file-seek", "guest-file-flush",
         "guest-suspend-hybrid", "guest-network-get-interfaces",
         "guest-get-vcpus", "guest-set-vcpus",
+        "guest-set-user-password",
         "guest-fsfreeze-freeze-list", "guest-get-fsinfo",
         "guest-fstrim", NULL};
     char **p = (char **)list_unsupported;
diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
index 376e79f..5117b65 100644
--- a/qga/qapi-schema.json
+++ b/qga/qapi-schema.json
@@ -738,3 +738,30 @@
 ##
 { 'command': 'guest-get-fsinfo',
   'returns': ['GuestFilesystemInfo'] }
+
+##
+# @guest-set-user-password
+#
+# @username: the user account whose password to change
+# @password: the new password entry string, base64 encoded
+# @crypted: true if password is already crypt()d, false if raw
+#
+# If the @crypted flag is true, it is the caller's responsibility
+# to ensure the correct crypt() encryption scheme is used. This
+# command does not attempt to interpret or report on the encryption
+# scheme. Refer to the documentation of the guest operating system
+# in question to determine what is supported.
+#
+# Note all guest operating systems will support use of the
+# @crypted flag, as they may require the clear-text password
+#
+# The @password parameter must always be base64 encoded before
+# transmission, even if already crypt()d, to ensure it is 8-bit
+# safe when passed as JSON.
+#
+# Returns: Nothing on success.
+#
+# Since 2.3
+##
+{ 'command': 'guest-set-user-password',
+  'data': { 'username': 'str', 'password': 'str', 'crypted': 'bool' } }
-- 
2.1.0