rules: add a rule to set /dev/kvm access mode and ownership (systemd#5597)

keszybz · martinpitt · commit 5a664ca10f38 · 2017-03-27T12:34:24.000+02:00
Kernel default mode is 0600, but distributions change it to group kvm, mode either 0660 (e.g. Debian) or 0666 (e.g. Fedora). Both approaches have valid reasons (a stricter mode limits exposure to bugs in the kvm subsystem, a looser mode makes libvirt and other virtualization mechanisms work out of the box for unprivileged users over ssh). In Fedora the qemu package carries the relevant rule, but it's nicer to have it in systemd, so that the permissions are not dependent on the qemu package being installed. Use of packaged qemu binaries is not required to make use of /dev/kvm, e.g. it's possible to use a self-compiled qemu or some alternative. https://bugzilla.redhat.com/show_bug.cgi?id=1431876 To accomodate both approaches, add a rule to set the mode in 50-udev-default.rules, but allow the mode to be overridden with a --with-dev-kvm-mode configure rule. The default is 0660, as the (slightly) more secure option.
diff --git a/Makefile.am b/Makefile.am
@@ -3825,7 +3825,6 @@ dist_network_DATA = \
 	network/80-container-vz.network
 
 dist_udevrules_DATA += \
-	rules/50-udev-default.rules \
 	rules/60-block.rules \
 	rules/60-drm.rules \
 	rules/60-evdev.rules \
@@ -3843,6 +3842,7 @@ dist_udevrules_DATA += \
 	rules/80-net-setup-link.rules
 
 nodist_udevrules_DATA += \
+	rules/50-udev-default.rules \
 	rules/99-systemd.rules
 
 udevconfdir = $(sysconfdir)/udev
@@ -3853,6 +3853,7 @@ pkgconfigdata_DATA += \
 	src/udev/udev.pc
 
 EXTRA_DIST += \
+	rules/50-udev-default.rules.in \
 	rules/99-systemd.rules.in \
 	src/udev/udev.pc.in
 
@@ -6301,6 +6302,7 @@ substitutions = \
        '|KILL_USER_PROCESSES=$(KILL_USER_PROCESSES)|' \
        '|systemuidmax=$(SYSTEM_UID_MAX)|' \
        '|systemgidmax=$(SYSTEM_GID_MAX)|' \
+       '|DEV_KVM_MODE=$(DEV_KVM_MODE)|' \
        '|TTY_GID=$(TTY_GID)|' \
        '|systemsleepdir=$(systemsleepdir)|' \
        '|systemshutdowndir=$(systemshutdowndir)|' \
diff --git a/configure.ac b/configure.ac
@@ -1205,6 +1205,16 @@ AC_ARG_WITH(system-gid-max,
 AC_DEFINE_UNQUOTED(SYSTEM_GID_MAX, [$SYSTEM_GID_MAX], [Maximum System GID])
 AC_SUBST(SYSTEM_GID_MAX)
 
+# ------------------------------------------------------------------------------
+
+AC_ARG_WITH(dev-kvm-mode,
+        AS_HELP_STRING([--with-dev-kvm-mode=MODE],
+                [/dev/kvm access mode, defaults to "0660"]),
+        [DEV_KVM_MODE="$withval"],
+        [DEV_KVM_MODE="0660"])
+
+AC_SUBST(DEV_KVM_MODE, [$DEV_KVM_MODE], [/dev/kvm access mode])
+
 # ------------------------------------------------------------------------------
 have_localed=no
 AC_ARG_ENABLE(localed, AS_HELP_STRING([--disable-localed], [disable locale daemon]))
@@ -1767,6 +1777,7 @@ AC_MSG_RESULT([
         TTY GID:                           ${TTY_GID}
         maximum system UID:                ${SYSTEM_UID_MAX}
         maximum system GID:                ${SYSTEM_GID_MAX}
+        /dev/kvm access mode:              ${DEV_KVM_MODE}
         certificate root:                  ${CERTIFICATEROOT}
         support URL:                       ${SUPPORT_URL}
         nobody user name:                  ${NOBODY_USER_NAME}
diff --git a/rules/.gitignore b/rules/.gitignore
@@ -1 +1,2 @@
+/50-udev-default.rules
 /99-systemd.rules
diff --git a/rules/50-udev-default.rules.in b/rules/50-udev-default.rules.in
@@ -74,6 +74,8 @@ KERNEL=="tun", MODE="0666", OPTIONS+="static_node=net/tun"
 
 KERNEL=="fuse", MODE="0666", OPTIONS+="static_node=fuse"
 
+KERNEL=="kvm", GROUP="kvm", MODE="@DEV_KVM_MODE@"
+
 SUBSYSTEM=="ptp", ATTR{clock_name}=="KVM virtual PTP", SYMLINK += "ptp_kvm"
 
 LABEL="default_end"
diff --git a/sysusers.d/basic.conf.in b/sysusers.d/basic.conf.in
@@ -29,6 +29,7 @@ g dialout -     -            -
 g disk    -     -            -
 g input   -     -            -
 g lp      -     -            -
+g kvm     -     -            -
 g tape    -     -            -
 g video   -     -            -
 

Original file line number	Diff line number	Diff line change
`@@ -1 +1,2 @@`
	`1`	`+/50-udev-default.rules`
`1`	`2`	`/99-systemd.rules`