tmpfiles: introduce the concept of unsafe operations

Various operations done by systemd-tmpfiles may only be safely done at
boot (e.g. removal of X lockfiles in /tmp, creation of /run/nologin).
Other operations may be done at any point in time (e.g. setting the
ownership on /{run,var}/log/journal). This distinction is largely
orthogonal to the type of operation.

A new switch --unsafe is added, and operations which should only be
executed during bootup are marked with an exclamation mark in the
configuration files. systemd-tmpfiles.service is modified to use this
switch, and guards are added so it is hard to re-start it by mistake.

If we install a new version of systemd, we actually want to enforce
some changes to tmpfiles configuration immediately. This should now be
possible to do safely, so distribution packages can be modified to
execute the "safe" subset at package installation time.

/run/nologin creation is split out into a separate service, to make it
easy to override.

https://bugzilla.redhat.com/show_bug.cgi?id=1043212
https://bugzilla.redhat.com/show_bug.cgi?id=1045849

9 files changed, 71 insertions, 12 deletions

diff --git a/Makefile.am b/Makefile.am
index f4b19589a1..b7a4681447 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1584,6 +1584,7 @@ nodist_systemunit_DATA += \
 
 dist_tmpfiles_DATA = \
 	tmpfiles.d/systemd.conf \
+	tmpfiles.d/systemd-nologin.conf \
 	tmpfiles.d/tmp.conf \
 	tmpfiles.d/x11.conf
 
diff --git a/man/systemd-tmpfiles.xml b/man/systemd-tmpfiles.xml
index c65636b0fe..9b8932c635 100644
--- a/man/systemd-tmpfiles.xml
+++ b/man/systemd-tmpfiles.xml
@@ -147,6 +147,12 @@
                                 removed.</para></listitem>
                         </varlistentry>
                         <varlistentry>
+                                <term><option>--unsafe</option></term>
+                                <listitem><para>Also execute lines
+                                with an exclamation mark.
+                                </para></listitem>
+                        </varlistentry>
+                        <varlistentry>
                                 <term><option>--prefix=PATH</option></term>
                                 <listitem><para>Only apply rules that
                                 apply to paths with the specified
diff --git a/man/tmpfiles.d.xml b/man/tmpfiles.d.xml
index 331fd1b472..0da52aedad 100644
--- a/man/tmpfiles.d.xml
+++ b/man/tmpfiles.d.xml
@@ -113,6 +113,9 @@ L    /tmp/foobar -    -    -    -   /dev/null</programlisting>
                 <refsect2>
                         <title>Type</title>
 
+                        <para>The type consists of a single letter and
+                        optionally an exclamation mark.</para>
+
                         <para>The following line types are understood:</para>
 
                         <variablelist>
@@ -262,6 +265,28 @@ L    /tmp/foobar -    -    -    -   /dev/null</programlisting>
                                         names.</para></listitem>
                                 </varlistentry>
                         </variablelist>
+
+                        <para>If the exclamation mark is used, this
+                        line is only safe of execute during boot, and
+                        can break a running system. Lines without the
+                        exclamation mark are presumed to be safe to
+                        execute at any time, e.g. on package upgrades.
+                        <command>systemd-tmpfiles</command> will
+                        execute line with an exclamation mark only if
+                        option <option>--unsafe</option> is given.
+                        </para>
+
+                        <para>For example:
+                        <programlisting>
+# Make sure these are created by default so that nobody else can
+d /tmp/.X11-unix 1777 root root 10d
+
+# Unlink the X11 lock files
+r! /tmp/.X[0-9]*-lock
+                        </programlisting>
+                        The second line in contrast to the first one
+                        would break a running system, and will only be
+                        executed with <option>--unsafe</option>.</para>
                 </refsect2>
 
                 <refsect2>
diff --git a/src/tmpfiles/tmpfiles.c b/src/tmpfiles/tmpfiles.c
index 02351e18f7..881c3b0d78 100644
--- a/src/tmpfiles/tmpfiles.c
+++ b/src/tmpfiles/tmpfiles.c
@@ -107,6 +107,7 @@ static Set *unix_sockets = NULL;
 static bool arg_create = false;
 static bool arg_clean = false;
 static bool arg_remove = false;
+static bool arg_unsafe = false;
 
 static char **include_prefixes = NULL;
 static char **exclude_prefixes = NULL;
@@ -1077,7 +1078,7 @@ static int parse_line(const char *fname, unsigned line, const char *buffer) {
         _cleanup_item_free_ Item *i = NULL;
         Item *existing;
         _cleanup_free_ char
-                *mode = NULL, *user = NULL, *group = NULL, *age = NULL, *path = NULL;
+                *action = NULL, *mode = NULL, *user = NULL, *group = NULL, *age = NULL, *path = NULL;
         char type;
         Hashmap *h;
         int r, n = -1;
@@ -1087,8 +1088,8 @@ static int parse_line(const char *fname, unsigned line, const char *buffer) {
         assert(buffer);
 
         r = sscanf(buffer,
-                   "%c %ms %ms %ms %ms %ms %n",
-                   &type,
+                   "%ms %ms %ms %ms %ms %ms %n",
+                   &action,
                    &path,
                    &mode,
                    &user,
@@ -1100,6 +1101,14 @@ static int parse_line(const char *fname, unsigned line, const char *buffer) {
                 return -EIO;
         }
 
+        if (strlen(action) > 2 || (strlen(action) > 1 && action[1] != '!')) {
+                log_error("[%s:%u] Unknown modifier '%s'", fname, line, action);
+                return -EINVAL;
+        } else if (strlen(action) > 1 && !arg_unsafe)
+                return 0;
+
+        type = action[0];
+
         i = new0(Item, 1);
         if (!i)
                 return log_oom();
@@ -1271,6 +1280,7 @@ static int help(void) {
                "     --create               Create marked files/directories\n"
                "     --clean                Clean up marked directories\n"
                "     --remove               Remove marked files/directories\n"
+               "     --unsafe               Execute actions only safe at boot\n"
                "     --prefix=PATH          Only apply rules that apply to paths with the specified prefix\n"
                "     --exclude-prefix=PATH  Ignore rules that apply to paths with the specified prefix\n",
                program_invocation_short_name);
@@ -1285,6 +1295,7 @@ static int parse_argv(int argc, char *argv[]) {
                 ARG_CREATE,
                 ARG_CLEAN,
                 ARG_REMOVE,
+                ARG_UNSAFE,
                 ARG_PREFIX,
                 ARG_EXCLUDE_PREFIX,
         };
@@ -1295,6 +1306,7 @@ static int parse_argv(int argc, char *argv[]) {
                 { "create",         no_argument,         NULL, ARG_CREATE         },
                 { "clean",          no_argument,         NULL, ARG_CLEAN          },
                 { "remove",         no_argument,         NULL, ARG_REMOVE         },
+                { "unsafe",         no_argument,         NULL, ARG_UNSAFE         },
                 { "prefix",         required_argument,   NULL, ARG_PREFIX         },
                 { "exclude-prefix", required_argument,   NULL, ARG_EXCLUDE_PREFIX },
                 {}
@@ -1329,6 +1341,10 @@ static int parse_argv(int argc, char *argv[]) {
                         arg_remove = true;
                         break;
 
+                case ARG_UNSAFE:
+                        arg_unsafe = true;
+                        break;
+
                 case ARG_PREFIX:
                         if (strv_extend(&include_prefixes, optarg) < 0)
                                 return log_oom();
diff --git a/tmpfiles.d/legacy.conf b/tmpfiles.d/legacy.conf
index 3fff347db4..a1656873da 100644
--- a/tmpfiles.d/legacy.conf
+++ b/tmpfiles.d/legacy.conf
@@ -29,6 +29,6 @@ d /run/lock/lockdev 0775 root lock -
 # kernel command line options 'fsck.mode=force', 'fsck.mode=skip' and
 # 'quotacheck.mode=force'
 
-r /forcefsck
-r /fastboot
-r /forcequotacheck
+r! /forcefsck
+r! /fastboot
+r! /forcequotacheck
diff --git a/tmpfiles.d/systemd-nologin.conf b/tmpfiles.d/systemd-nologin.conf
new file mode 100644
index 0000000000..d61232b534
--- /dev/null
+++ b/tmpfiles.d/systemd-nologin.conf
@@ -0,0 +1,11 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+# See tmpfiles.d(5) and systemd-forbid-user-logins.service(5).
+# This file has special suffix so it is not run by mistake.
+
+F! /run/nologin 0644 - - - "System is booting up. See pam_nologin(8)"
diff --git a/tmpfiles.d/systemd.conf b/tmpfiles.d/systemd.conf
index a05c6577d2..7c6d6b9099 100644
--- a/tmpfiles.d/systemd.conf
+++ b/tmpfiles.d/systemd.conf
@@ -8,7 +8,7 @@
 # See tmpfiles.d(5) for details
 
 d /run/user 0755 root root ~10d
-F /run/utmp 0664 root utmp -
+F! /run/utmp 0664 root utmp -
 
 f /var/log/wtmp 0664 root utmp -
 f /var/log/btmp 0600 root utmp -
@@ -22,8 +22,6 @@ d /run/systemd/users 0755 root root -
 d /run/systemd/machines 0755 root root -
 d /run/systemd/shutdown 0755 root root -
 
-F /run/nologin 0644 - - - "System is booting up. See pam_nologin(8)"
-
 m /var/log/journal 2755 root systemd-journal - -
 m /var/log/journal/%m 2755 root systemd-journal - -
 m /run/log/journal 2755 root systemd-journal - -
diff --git a/tmpfiles.d/x11.conf b/tmpfiles.d/x11.conf
index ece6a5ce98..4c96a54a13 100644
--- a/tmpfiles.d/x11.conf
+++ b/tmpfiles.d/x11.conf
@@ -15,4 +15,4 @@ d /tmp/.font-unix 1777 root root 10d
 d /tmp/.Test-unix 1777 root root 10d
 
 # Unlink the X11 lock files
-r /tmp/.X[0-9]*-lock
+r! /tmp/.X[0-9]*-lock
diff --git a/units/systemd-tmpfiles-setup.service.in b/units/systemd-tmpfiles-setup.service.in
index 3405e2842c..c2dcae0e13 100644
--- a/units/systemd-tmpfiles-setup.service.in
+++ b/units/systemd-tmpfiles-setup.service.in
@@ -6,7 +6,7 @@
 #  (at your option) any later version.
 
 [Unit]
-Description=Recreate Volatile Files and Directories
+Description=Create Volatile Files and Directories
 Documentation=man:tmpfiles.d(5) man:systemd-tmpfiles(8)
 DefaultDependencies=no
 Wants=local-fs.target
@@ -18,8 +18,10 @@ ConditionDirectoryNotEmpty=|/lib/tmpfiles.d
 ConditionDirectoryNotEmpty=|/usr/local/lib/tmpfiles.d
 ConditionDirectoryNotEmpty=|/etc/tmpfiles.d
 ConditionDirectoryNotEmpty=|/run/tmpfiles.d
+RefuseManualStart=yes
+RefuseManualStop=yes
 
 [Service]
 Type=oneshot
 RemainAfterExit=yes
-ExecStart=@rootbindir@/systemd-tmpfiles --create --remove --exclude-prefix=/dev
+ExecStart=@rootbindir@/systemd-tmpfiles --create --remove --unsafe --exclude-prefix=/dev