From e5fd6fcb30e673e29576be205e80e7bf8cbb135c Mon Sep 17 00:00:00 2001
From: Hans de Goede <hdegoede@redhat.com>
Date: Tue, 12 Jun 2018 13:25:16 +0200
Subject: [PATCH] Add grub-set-bootflag utility

This commit adds a new grub-set-bootflag utility, which can be used
to set known bootflags in the grubenv: boot_success or menu_show_once.

grub-set-bootflag is different from grub-editenv in 2 ways:

1) It is intended to be executed by regular users through pkexec, so
running as root if the polkit policy allows this. As such it is written
to not use any existing grubenv related code for easy auditing.

2) Since it can be executed by regular users it only allows setting
(assigning a value of 1 to) bootflags which it knows about. Currently
those are just boot_success and menu_show_once.

This commit also adds a couple of example systemd and polkit files which
show how this can be used to set boot_success from a user-session:

docs/grub-boot-success.service
docs/grub-boot-success.timer
docs/org.gnu.grub.policy

The 2 grub-boot-success.systemd files should be placed in /lib/systemd/user
and a symlink to grub-boot-success.timer should be added to
/lib/systemd/user/timers.target.wants.

The org.gnu.grub.policy polkit file should be placed in
/usr/share/polkit-1/actions.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 Makefile.util.def              |   7 ++
 util/grub-set-bootflag.c       | 158 +++++++++++++++++++++++++++++++++++++++++
 conf/Makefile.extra-dist       |   3 +
 docs/grub-boot-success.service |   6 ++
 docs/grub-boot-success.timer   |   5 ++
 docs/org.gnu.grub.policy       |  20 ++++++
 util/grub-set-bootflag.1       |  20 ++++++
 7 files changed, 219 insertions(+)
 create mode 100644 util/grub-set-bootflag.c
 create mode 100644 docs/grub-boot-success.service
 create mode 100644 docs/grub-boot-success.timer
 create mode 100644 docs/org.gnu.grub.policy
 create mode 100644 util/grub-set-bootflag.1

diff --git a/Makefile.util.def b/Makefile.util.def
index 57c51a27bc4..72be14449c5 100644
--- a/Makefile.util.def
+++ b/Makefile.util.def
@@ -1429,3 +1429,10 @@ program = {
   ldadd = grub-core/gnulib/libgnu.a;
   ldadd = '$(LIBINTL) $(LIBDEVMAPPER) $(LIBZFS) $(LIBNVPAIR) $(LIBGEOM)';
 };
+
+program = {
+  name = grub-set-bootflag;
+  installdir = sbin;
+  mansection = 1;
+  common = util/grub-set-bootflag.c;
+};
diff --git a/util/grub-set-bootflag.c b/util/grub-set-bootflag.c
new file mode 100644
index 00000000000..f8dc310909a
--- /dev/null
+++ b/util/grub-set-bootflag.c
@@ -0,0 +1,158 @@
+/* grub-set-bootflag.c - tool to set boot-flags in the grubenv. */
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2018 Free Software Foundation, Inc.
+ *
+ *  GRUB 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.
+ *
+ *  GRUB 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 GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * NOTE this gets run by users as root (through pkexec), so this does not
+ * use any grub library / util functions to allow for easy auditing.
+ * The grub headers are only included to get certain defines.
+ */
+
+#include <config-util.h>     /* For *_DIR_NAME defines */
+#include <grub/types.h>
+#include <grub/lib/envblk.h> /* For GRUB_ENVBLK_DEFCFG define */
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#define GRUBENV "/" GRUB_BOOT_DIR_NAME "/" GRUB_DIR_NAME "/" GRUB_ENVBLK_DEFCFG
+#define GRUBENV_SIZE 1024
+
+const char *bootflags[] = {
+  "boot_success",
+  "menu_show_once",
+  NULL
+};
+
+static void usage(void)
+{
+  int i;
+
+  fprintf (stderr, "Usage: 'grub-set-bootflag <bootflag>', where <bootflag> is one of:\n");
+  for (i = 0; bootflags[i]; i++)
+    fprintf (stderr, "  %s\n", bootflags[i]);
+}
+
+int main(int argc, char *argv[])
+{
+  /* NOTE buf must be at least the longest bootflag length + 4 bytes */
+  char env[GRUBENV_SIZE + 1], buf[64], *s;
+  const char *bootflag;
+  int i, len, ret;
+  FILE *f;
+
+  if (argc != 2)
+    {
+      usage();
+      return 1;
+    }
+
+  for (i = 0; bootflags[i]; i++)
+    if (!strcmp (argv[1], bootflags[i]))
+      break;
+  if (!bootflags[i])
+    {
+      fprintf (stderr, "Invalid bootflag: '%s'\n", argv[1]);
+      usage();
+      return 1;
+    }
+
+  bootflag = bootflags[i];
+  len = strlen (bootflag);
+
+  f = fopen (GRUBENV, "r");
+  if (!f)
+    {
+      perror ("Error opening " GRUBENV " for reading");
+      return 1;     
+    }
+
+  ret = fread (env, 1, GRUBENV_SIZE, f);
+  fclose (f);
+  if (ret != GRUBENV_SIZE)
+    {
+      perror ("Error reading from " GRUBENV);
+      return 1;     
+    }
+
+  /* 0 terminate env */
+  env[GRUBENV_SIZE] = 0;
+
+  if (strncmp (env, GRUB_ENVBLK_SIGNATURE, strlen (GRUB_ENVBLK_SIGNATURE)))
+    {
+      fprintf (stderr, "Error invalid environment block\n");
+      return 1;
+    }
+
+  /* Find a pre-existing definition of the bootflag */
+  s = strstr (env, bootflag);
+  while (s && s[len] != '=')
+    s = strstr (s + len, bootflag);
+
+  if (s && ((s[len + 1] != '0' && s[len + 1] != '1') || s[len + 2] != '\n'))
+    {
+      fprintf (stderr, "Pre-existing bootflag '%s' has unexpected value\n", bootflag);
+      return 1;     
+    }
+
+  /* No pre-existing bootflag? -> find free space */
+  if (!s)
+    {
+      for (i = 0; i < (len + 3); i++)
+        buf[i] = '#';
+      buf[i] = 0;
+      s = strstr (env, buf);
+    }
+
+  if (!s)
+    {
+      fprintf (stderr, "No space in grubenv to store bootflag '%s'\n", bootflag);
+      return 1;     
+    }
+
+  /* The grubenv is not 0 terminated, so memcpy the name + '=' , '1', '\n' */
+  snprintf(buf, sizeof(buf), "%s=1\n", bootflag);
+  memcpy(s, buf, len + 3);
+
+  /* "r+", don't truncate so that the diskspace stays reserved */
+  f = fopen (GRUBENV, "r+");
+  if (!f)
+    {
+      perror ("Error opening " GRUBENV " for writing");
+      return 1;     
+    }
+
+  ret = fwrite (env, 1, GRUBENV_SIZE, f);
+  if (ret != GRUBENV_SIZE)
+    {
+      perror ("Error writing to " GRUBENV);
+      return 1;     
+    }
+
+  ret = fflush (f);
+  if (ret)
+    {
+      perror ("Error flushing " GRUBENV);
+      return 1;     
+    }
+
+  fsync (fileno (f));
+  fclose (f);
+
+  return 0;
+}
diff --git a/conf/Makefile.extra-dist b/conf/Makefile.extra-dist
index 39eb94bded6..5946ec24a65 100644
--- a/conf/Makefile.extra-dist
+++ b/conf/Makefile.extra-dist
@@ -14,6 +14,9 @@ EXTRA_DIST += util/import_unicode.py
 EXTRA_DIST += docs/autoiso.cfg
 EXTRA_DIST += docs/grub.cfg
 EXTRA_DIST += docs/osdetect.cfg
+EXTRA_DIST += docs/org.gnu.grub.policy
+EXTRA_DIST += docs/grub-boot-success.service
+EXTRA_DIST += docs/grub-boot-success.timer
 
 EXTRA_DIST += conf/i386-cygwin-img-ld.sc
 
diff --git a/docs/grub-boot-success.service b/docs/grub-boot-success.service
new file mode 100644
index 00000000000..c8c91c34d49
--- /dev/null
+++ b/docs/grub-boot-success.service
@@ -0,0 +1,6 @@
+[Unit]
+Description=Mark boot as successful
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/pkexec /usr/sbin/grub2-set-bootflag boot_success
diff --git a/docs/grub-boot-success.timer b/docs/grub-boot-success.timer
new file mode 100644
index 00000000000..221b532781b
--- /dev/null
+++ b/docs/grub-boot-success.timer
@@ -0,0 +1,5 @@
+[Unit]
+Description=Mark boot as successful after the user session has run 2 minutes
+
+[Timer]
+OnActiveSec=2min
diff --git a/docs/org.gnu.grub.policy b/docs/org.gnu.grub.policy
new file mode 100644
index 00000000000..18391efc8e7
--- /dev/null
+++ b/docs/org.gnu.grub.policy
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE policyconfig PUBLIC "-//freedesktop//DTD PolicyKit Policy Configuration 1.0//EN" "http://www.freedesktop.org/standards/PolicyKit/1.0/policyconfig.dtd">
+<policyconfig>
+  <vendor>GNU GRUB</vendor>
+  <vendor_url>https://www.gnu.org/software/grub/</vendor_url>
+  <action id="org.gnu.grub.set-bootflag">
+    <!-- SECURITY:
+          - A normal active user on the local machine does not need permission
+            to set bootflags to show the menu / mark current boot successful.
+     -->
+    <description>Set GRUB bootflags</description>
+    <message>Authentication is required to modify the bootloaders bootflags</message>
+    <defaults>
+      <allow_any>no</allow_any>
+      <allow_inactive>no</allow_inactive>
+      <allow_active>yes</allow_active>
+    </defaults>
+    <annotate key="org.freedesktop.policykit.exec.path">/usr/sbin/grub2-set-bootflag</annotate>
+  </action>
+</policyconfig>
diff --git a/util/grub-set-bootflag.1 b/util/grub-set-bootflag.1
new file mode 100644
index 00000000000..57801da22a0
--- /dev/null
+++ b/util/grub-set-bootflag.1
@@ -0,0 +1,20 @@
+.TH GRUB-SET-BOOTFLAG 1 "Tue Jun 12 2018"
+.SH NAME
+\fBgrub-set-bootflag\fR \(em Set a bootflag in the GRUB environment block.
+
+.SH SYNOPSIS
+\fBgrub-set-bootflag\fR <\fIBOOTFLAG\fR>
+
+.SH DESCRIPTION
+\fBgrub-set-bootflag\fR is a command line to set bootflags in GRUB's
+stored environment.
+
+.SH COMMANDS
+.TP
+\fBBOOTFLAG\fR
+.RS 7
+Bootflag to set, one of \fIboot_success\fR or \fIshow_menu_once\fR.
+.RE
+
+.SH SEE ALSO
+.BR "info grub"