From de8f6fb530db706d14e9ece52b2acfd77c823133 Mon Sep 17 00:00:00 2001

From: Kristijan Gjoshev <crypter@mail.com>

Date: Sat, 1 Feb 2020 18:27:08 +0100

Subject: [PATCH 3/3] timer: add new feature FixedRandomDelay=

FixedRandomDelay=yes will use

`siphash24(sd_id128_get_machine() || MANAGER_IS_SYSTEM(m) || getuid() || u->id)`,

where || is concatenation, instead of a random number to choose a value between

0 and RandomizedDelaySec= as the timer delay.

This essentially sets up a fixed, but seemingly random, offset for each timer

iteration rather than having a random offset recalculated each time it fires.

Closes #10355

Co-author: Anita Zhang <the.anitazha@gmail.com>

---

 docs/TRANSIENT-SETTINGS.md                    |  1 +

 man/org.freedesktop.systemd1.xml              |  6 ++++

 man/systemd.timer.xml                         | 12 +++++++

 src/core/dbus-timer.c                         |  4 +++

 src/core/timer.c                              | 34 ++++++++++++++++++-

 src/core/timer.h                              |  1 +

 src/shared/bus-unit-util.c                    |  3 +-

 test/fuzz/fuzz-unit-file/directives.service   |  1 +

 .../systemd-tmpfiles-clean.timer              |  1 +

 9 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/docs/TRANSIENT-SETTINGS.md b/docs/TRANSIENT-SETTINGS.md

index 19944d08b8..f4639b2e87 100644

--- a/docs/TRANSIENT-SETTINGS.md

+++ b/docs/TRANSIENT-SETTINGS.md

@@ -368,6 +368,7 @@ Most timer unit settings are available to transient units.

 ✓ RemainAfterElapse=

 ✓ AccuracySec=

 ✓ RandomizedDelaySec=

+✓ FixedRandomDelay=

   Unit=

 ```

diff --git a/man/org.freedesktop.systemd1.xml b/man/org.freedesktop.systemd1.xml

index 6b16ae16da..ab4cbaa2fb 100644

--- a/man/org.freedesktop.systemd1.xml

+++ b/man/org.freedesktop.systemd1.xml

@@ -6866,6 +6866,8 @@ node /org/freedesktop/systemd1/unit/systemd_2dtmpfiles_2dclean_2etimer {

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly t RandomizedDelayUSec = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

+      readonly b FixedRandomDelay = ...;

+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b Persistent = ...;

       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")

       readonly b WakeSystem = ...;

@@ -6891,6 +6893,8 @@ node /org/freedesktop/systemd1/unit/systemd_2dtmpfiles_2dclean_2etimer {

+    

+

@@ -6931,6 +6935,8 @@ node /org/freedesktop/systemd1/unit/systemd_2dtmpfiles_2dclean_2etimer {

     <variablelist class="dbus-property" generated="True" extra-ref="RandomizedDelayUSec"/>

+    <variablelist class="dbus-property" generated="True" extra-ref="FixedRandomDelay"/>

+

     <variablelist class="dbus-property" generated="True" extra-ref="Persistent"/>

     <variablelist class="dbus-property" generated="True" extra-ref="WakeSystem"/>

diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml

index 5822402712..6f731e2311 100644

--- a/man/systemd.timer.xml

+++ b/man/systemd.timer.xml

@@ -268,6 +268,18 @@

         <varname>AccuracySec=1us</varname>.</para></listitem>

       </varlistentry>

+      <varlistentry>

+        <term><varname>FixedRandomDelay=</varname></term>

+

+        <listitem><para>Takes a boolean argument. If true, some amount of time between 0 and

+        <varname>RandomizedDelaySec=</varname> is chosen and added as the delay for each timer iteration. As this

+        delay will not be recalculated on each run, this effectively creates a fixed offset for each iteration.

+        The distribution between 0 and <varname>RandomizedDelaySec=</varname> is deterministic and based on

+        a combination of the machine ID, whether the timer is run by the user/system manager, the service manager's

+        user ID, and the timer's unit name. Has no effect if

+        <varname>RandomizedDelaySec=</varname> is set to 0. Defaults to <option>false</option>.</para></listitem>

+      </varlistentry>

+

       <varlistentry>

         <term><varname>OnClockChange=</varname></term>

         <term><varname>OnTimezoneChange=</varname></term>

diff --git a/src/core/dbus-timer.c b/src/core/dbus-timer.c

index da35fa8678..ee54ba8772 100644

--- a/src/core/dbus-timer.c

+++ b/src/core/dbus-timer.c

@@ -131,6 +131,7 @@ const sd_bus_vtable bus_timer_vtable[] = {

         SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Timer, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),

         SD_BUS_PROPERTY("AccuracyUSec", "t", bus_property_get_usec, offsetof(Timer, accuracy_usec), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("RandomizedDelayUSec", "t", bus_property_get_usec, offsetof(Timer, random_usec), SD_BUS_VTABLE_PROPERTY_CONST),

+        SD_BUS_PROPERTY("FixedRandomDelay", "b", bus_property_get_bool, offsetof(Timer, fixed_random_delay), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("Persistent", "b", bus_property_get_bool, offsetof(Timer, persistent), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("WakeSystem", "b", bus_property_get_bool, offsetof(Timer, wake_system), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("RemainAfterElapse", "b", bus_property_get_bool, offsetof(Timer, remain_after_elapse), SD_BUS_VTABLE_PROPERTY_CONST),

@@ -232,6 +233,9 @@ static int bus_timer_set_transient_property(

         if (streq(name, "RandomizedDelayUSec"))

                 return bus_set_transient_usec(u, name, &t->random_usec, message, flags, error);

+        if (streq(name, "FixedRandomDelay"))

+                return bus_set_transient_bool(u, name, &t->fixed_random_delay, message, flags, error);

+

         if (streq(name, "WakeSystem"))

                 return bus_set_transient_bool(u, name, &t->wake_system, message, flags, error);

diff --git a/src/core/timer.c b/src/core/timer.c

index 03a9c14f76..b2c5e26f63 100644

--- a/src/core/timer.c

+++ b/src/core/timer.c

@@ -169,6 +169,36 @@ static int timer_setup_persistent(Timer *t) {

         return 0;

 }

+static uint64_t timer_get_fixed_delay_hash(Timer *t) {

+        static const uint8_t hash_key[] = {

+                0x51, 0x0a, 0xdb, 0x76, 0x29, 0x51, 0x42, 0xc2,

+                0x80, 0x35, 0xea, 0xe6, 0x8e, 0x3a, 0x37, 0xbd

+        };

+

+        struct siphash state;

+        sd_id128_t machine_id;

+        uid_t uid;

+        int r;

+

+        assert(t);

+

+        uid = getuid();

+        r = sd_id128_get_machine(&machine_id);

+        if (r < 0) {

+                log_unit_debug_errno(UNIT(t), r,

+                                     "Failed to get machine ID for the fixed delay calculation, proceeding with 0: %m");

+                machine_id = SD_ID128_NULL;

+        }

+

+        siphash24_init(&state, hash_key);

+        siphash24_compress(&machine_id, sizeof(sd_id128_t), &state);

+        siphash24_compress_boolean(MANAGER_IS_SYSTEM(UNIT(t)->manager), &state);

+        siphash24_compress(&uid, sizeof(uid_t), &state);

+        siphash24_compress_string(UNIT(t)->id, &state);

+

+        return siphash24_finalize(&state);

+}

+

 static int timer_load(Unit *u) {

         Timer *t = TIMER(u);

         int r;

@@ -215,6 +245,7 @@ static void timer_dump(Unit *u, FILE *f, const char *prefix) {

                 "%sWakeSystem: %s\n"

                 "%sAccuracy: %s\n"

                 "%sRemainAfterElapse: %s\n"

+                "%sFixedRandomDelay: %s\n"

                 "%sOnClockChange: %s\n"

                 "%sOnTimeZoneChange: %s\n",

                 prefix, timer_state_to_string(t->state),

@@ -224,6 +255,7 @@ static void timer_dump(Unit *u, FILE *f, const char *prefix) {

                 prefix, yes_no(t->wake_system),

                 prefix, format_timespan(buf, sizeof(buf), t->accuracy_usec, 1),

                 prefix, yes_no(t->remain_after_elapse),

+                prefix, yes_no(t->fixed_random_delay),

                 prefix, yes_no(t->on_clock_change),

                 prefix, yes_no(t->on_timezone_change));

@@ -332,7 +364,7 @@ static void add_random(Timer *t, usec_t *v) {

         if (*v == USEC_INFINITY)

                 return;

-        add = random_u64() % t->random_usec;

+        add = (t->fixed_random_delay ? timer_get_fixed_delay_hash(t) : random_u64()) % t->random_usec;

         if (*v + add < *v) /* overflow */

                 *v = (usec_t) -2; /* Highest possible value, that is not USEC_INFINITY */

diff --git a/src/core/timer.h b/src/core/timer.h

index ab66a201ad..ce4046a210 100644

--- a/src/core/timer.h

+++ b/src/core/timer.h

@@ -59,6 +59,7 @@ struct Timer {

         bool remain_after_elapse;

         bool on_clock_change;

         bool on_timezone_change;

+        bool fixed_random_delay;

         char *stamp_path;

 };

diff --git a/src/shared/bus-unit-util.c b/src/shared/bus-unit-util.c

index f2652ed9a5..68de4a2ed1 100644

--- a/src/shared/bus-unit-util.c

+++ b/src/shared/bus-unit-util.c

@@ -1779,7 +1779,8 @@ static int bus_append_timer_property(sd_bus_message *m, const char *field, const

                               "RemainAfterElapse",

                               "Persistent",

                               "OnTimezoneChange",

-                              "OnClockChange"))

+                              "OnClockChange",

+                              "FixedRandomDelay"))

                 return bus_append_parse_boolean(m, field, eq);

         if (STR_IN_SET(field, "AccuracySec",

diff --git a/test/fuzz/fuzz-unit-file/directives.service b/test/fuzz/fuzz-unit-file/directives.service

index dbff9ab2cc..95304ea0c6 100644

--- a/test/fuzz/fuzz-unit-file/directives.service

+++ b/test/fuzz/fuzz-unit-file/directives.service

@@ -175,6 +175,7 @@ PipeSize=

 Priority=

 PropagatesReloadTo=

 RandomizedDelaySec=

+FixedRandomDelay=

 RebootArgument=

 ReceiveBuffer=

 RefuseManualStart=

diff --git a/test/fuzz/fuzz-unit-file/systemd-tmpfiles-clean.timer b/test/fuzz/fuzz-unit-file/systemd-tmpfiles-clean.timer

index 7db361cd69..64b8808adc 100644

--- a/test/fuzz/fuzz-unit-file/systemd-tmpfiles-clean.timer

+++ b/test/fuzz/fuzz-unit-file/systemd-tmpfiles-clean.timer

@@ -32,6 +32,7 @@ OnCalendar=Fri 2012-11-23 11:12:13

 Persistent=true

 AccuracySec=24h

 RandomizedDelaySec=234234234

+FixedRandomDelay=true

 Persistent=no

 Unit=foo.service

-- 

2.24.1