journald: introduce new "systemd-journal" group and make it own the journal files

Previously all journal files were owned by "adm". In order to allow
specific users to read the journal files without granting it access to
the full "adm" powers, introduce a new specific group for this.

"systemd-journal" has to be created by the packaging scripts manually at
installation time. It's a good idea to assign a static UID/GID to this
group, since /var/log/journal might be shared across machines via NFS.

This commit also grants read access to the journal files by default to
members of the "wheel" and "adm" groups via file system ACLs, since
these "almost-root" groups should be able to see what's going on on the
system. These ACLs are created by "make install". Packagers probably
need to duplicate this logic in their postinst scripts.

This also adds documentation how to grant access to the journal to
additional users or groups via fs ACLs.

5 files changed, 64 insertions, 11 deletions

diff --git a/Makefile.am b/Makefile.am
index 3d3f2652f6..13211c45bd 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -2563,9 +2563,16 @@ libsystemd_journal_internal_la_LIBADD += \
 	$(GCRYPT_LIBS)
 endif
 
-# move lib from $(libdir) to $(rootlibdir) and update devel link, if needed
+# move lib from $(libdir) to $(rootlibdir) and update devel link, if
+# needed. Also, grant read access to new journal files to members of
+# "adm" and "wheel".
 libsystemd-journal-install-hook:
 	libname=libsystemd-journal.so && $(move-to-rootlibdir)
+	$(MKDIR_P) $(DESTDIR)/var/log/journal
+	-chown 0:0 $(DESTDIR)/var/log/journal
+	-chmod 755 $(DESTDIR)/var/log/journal
+	-setfacl -nm g:adm:rx,d:g:adm:rx $(DESTDIR)/var/log/journal/
+	-setfacl -nm g:wheel:rx,d:g:wheel:rx $(DESTDIR)/var/log/journal/
 
 libsystemd-journal-uninstall-hook:
 	rm -f $(DESTDIR)$(rootlibdir)/libsystemd-journal.so*
diff --git a/README b/README
index d8b1b1296a..300a4cf8bc 100644
--- a/README
+++ b/README
@@ -100,6 +100,19 @@ REQUIREMENTS:
         being 'html' or 'latexpdf'. If using DESTDIR for installation,
         pass the same DESTDIR to 'make sphinx-html' invocation.
 
+USERS AND GROUPS:
+        During runtime the journal daemon requires the
+        "system-journal" system group to exist. New journal files will
+        be readable by this group (but not writable) which may be used
+        to grant specific users read access.
+
+        It is also recommended to grant read access to all journal
+        files to the system groups "wheel" and "adm" with a command
+        like the following in the post installation script of the
+        package:
+
+        # setfacl -nm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/
+
 WARNINGS:
         systemd will warn you during boot if /etc/mtab is not a
         symlink to /proc/mounts. Please ensure that /etc/mtab is a
diff --git a/man/systemd-journald.service.xml b/man/systemd-journald.service.xml
index 4969ab19c3..bc32c8e38b 100644
--- a/man/systemd-journald.service.xml
+++ b/man/systemd-journald.service.xml
@@ -158,6 +158,38 @@
                 </variablelist>
         </refsect1>
 
+        <refsect1>
+                <title>Access Control</title>
+
+                <para>Journal files are by default owned and readable
+                by the <literal>systemd-journal</literal> system group
+                (but not writable). Adding a user to this group thus
+                enables her/him to read the journal files.</para>
+
+                <para>By default, each logged in user will get her/his
+                own set of journal files in
+                <filename>/var/log/journal/</filename>. These files
+                will not be owned by the user however, in order to
+                avoid that the user can write to them
+                directly. Instead, file system ACLs are used to ensure
+                the user gets read access only.</para>
+
+                <para>Additional users and groups may be granted
+                access to journal files via file system access control
+                lists (ACL). Distributions and administrators may
+                choose to grant read access to all members of the
+                <literal>wheel</literal> and <literal>adm</literal>
+                system groups with a command such as the
+                following:</para>
+
+                <programlisting># setfacl -Rnm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/</programlisting>
+
+                <para>Note that this command will update the ACLs both
+                for existing journal files and for future journal
+                files created in the
+                <filename>/var/log/journal/</filename>
+                directory.</para>
+        </refsect1>
 
         <refsect1>
                 <title>See Also</title>
@@ -166,7 +198,8 @@
                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                         <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                         <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
-                        <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                        <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>setfacl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                 </para>
         </refsect1>
 
diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index d898ae7179..cb93fea63b 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -870,16 +870,16 @@ static int verify(sd_journal *j) {
 static int access_check(void) {
 
 #ifdef HAVE_ACL
-        if (access("/var/log/journal", F_OK) < 0 && geteuid() != 0 && in_group("adm") <= 0) {
-                log_error("Unprivileged users can't see messages unless persistent log storage is enabled. Users in the group 'adm' can always see messages.");
+        if (access("/var/log/journal", F_OK) < 0 && geteuid() != 0 && in_group("systemd-journal") <= 0) {
+                log_error("Unprivileged users can't see messages unless persistent log storage is enabled. Users in the group 'systemd-journal' can always see messages.");
                 return -EACCES;
         }
 
-        if (!arg_quiet && geteuid() != 0 && in_group("adm") <= 0)
-                log_warning("Showing user generated messages only. Users in the group 'adm' can see all messages. Pass -q to turn this notice off.");
+        if (!arg_quiet && geteuid() != 0 && in_group("systemd-journal") <= 0)
+                log_warning("Showing user generated messages only. Users in the group 'systemd-journal' can see all messages. Pass -q to turn this notice off.");
 #else
-        if (geteuid() != 0 && in_group("adm") <= 0) {
-                log_error("No access to messages. Only users in the group 'adm' can see messages.");
+        if (geteuid() != 0 && in_group("systemd-journal") <= 0) {
+                log_error("No access to messages. Only users in the group 'systemd-journal' can see messages.");
                 return -EACCES;
         }
 #endif
diff --git a/src/journal/journald-server.c b/src/journal/journald-server.c
index 654f7ace21..ac565c7ece 100644
--- a/src/journal/journald-server.c
+++ b/src/journal/journald-server.c
@@ -174,7 +174,7 @@ static uint64_t available_space(Server *s) {
 }
 
 static void server_read_file_gid(Server *s) {
-        const char *adm = "adm";
+        const char *g = "systemd-journal";
         int r;
 
         assert(s);
@@ -182,9 +182,9 @@ static void server_read_file_gid(Server *s) {
         if (s->file_gid_valid)
                 return;
 
-        r = get_group_creds(&adm, &s->file_gid);
+        r = get_group_creds(&g, &s->file_gid);
         if (r < 0)
-                log_warning("Failed to resolve 'adm' group: %s", strerror(-r));
+                log_warning("Failed to resolve '%s' group: %s", g, strerror(-r));
 
         /* if we couldn't read the gid, then it will be 0, but that's
          * fine and we shouldn't try to resolve the group again, so