From d61bd956e599dd747490d36ff793b63fb6a9fedc Mon Sep 17 00:00:00 2001
From: Daan De Meyer <daan.j.demeyer@gmail.com>
Date: Fri, 17 Dec 2021 20:01:31 +0100
Subject: [PATCH] core: Add trigger limit for path units

When conditions fail on a service unit, a path unit can cause
PID 1 to busy loop as it keeps trying to activate the service unit.
To avoid this from happening, add a trigger limit to the path unit,
identical to the trigger limit we have for socket units.

Initially, let's start with a high limit and not make it configurable.
If needed, we can add properties to configure the rate limit similar
to the ones we have for socket units.

(cherry picked from commit aaae822b37aa3ca39aebb516fdc6bef36d730c25)

Resolves: #2123801
---
 src/core/path.c                            | 10 ++++++++++
 src/core/path.h                            |  3 +++
 test/TEST-63-ISSUE-17433/test63.service    |  2 +-
 test/TEST-63-ISSUE-17433/testsuite.service | 21 +++++++++++++++++----
 4 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/src/core/path.c b/src/core/path.c
index c2facf0b16..b899bde0de 100644
--- a/src/core/path.c
+++ b/src/core/path.c
@@ -238,6 +238,9 @@ static void path_init(Unit *u) {
         assert(u->load_state == UNIT_STUB);
 
         p->directory_mode = 0755;
+
+        p->trigger_limit.interval = 2 * USEC_PER_SEC;
+        p->trigger_limit.burst = 200;
 }
 
 void path_free_specs(Path *p) {
@@ -467,6 +470,12 @@ static void path_enter_running(Path *p) {
         if (unit_stop_pending(UNIT(p)))
                 return;
 
+        if (!ratelimit_below(&p->trigger_limit)) {
+                log_unit_warning(UNIT(p), "Trigger limit hit, refusing further activation.");
+                path_enter_dead(p, PATH_FAILURE_TRIGGER_LIMIT_HIT);
+                return;
+        }
+
         trigger = UNIT_TRIGGER(UNIT(p));
         if (!trigger) {
                 log_unit_error(UNIT(p), "Unit to trigger vanished.");
@@ -767,6 +776,7 @@ static const char* const path_result_table[_PATH_RESULT_MAX] = {
         [PATH_FAILURE_RESOURCES] = "resources",
         [PATH_FAILURE_START_LIMIT_HIT] = "start-limit-hit",
         [PATH_FAILURE_UNIT_START_LIMIT_HIT] = "unit-start-limit-hit",
+        [PATH_FAILURE_TRIGGER_LIMIT_HIT]    = "trigger-limit-hit",
 };
 
 DEFINE_STRING_TABLE_LOOKUP(path_result, PathResult);
diff --git a/src/core/path.h b/src/core/path.h
index 8a69f06c13..12fd13fbe3 100644
--- a/src/core/path.h
+++ b/src/core/path.h
@@ -46,6 +46,7 @@ typedef enum PathResult {
         PATH_FAILURE_RESOURCES,
         PATH_FAILURE_START_LIMIT_HIT,
         PATH_FAILURE_UNIT_START_LIMIT_HIT,
+        PATH_FAILURE_TRIGGER_LIMIT_HIT,
         _PATH_RESULT_MAX,
         _PATH_RESULT_INVALID = -1
 } PathResult;
@@ -63,6 +64,8 @@ struct Path {
         mode_t directory_mode;
 
         PathResult result;
+
+        RateLimit trigger_limit;
 };
 
 void path_free_specs(Path *p);
diff --git a/test/TEST-63-ISSUE-17433/test63.service b/test/TEST-63-ISSUE-17433/test63.service
index c83801874d..6292434c5c 100644
--- a/test/TEST-63-ISSUE-17433/test63.service
+++ b/test/TEST-63-ISSUE-17433/test63.service
@@ -1,5 +1,5 @@
 [Unit]
-ConditionPathExists=!/tmp/nonexistent
+ConditionPathExists=/tmp/nonexistent
 
 [Service]
 ExecStart=true
diff --git a/test/TEST-63-ISSUE-17433/testsuite.service b/test/TEST-63-ISSUE-17433/testsuite.service
index d3ca5b002b..39f9643890 100644
--- a/test/TEST-63-ISSUE-17433/testsuite.service
+++ b/test/TEST-63-ISSUE-17433/testsuite.service
@@ -4,14 +4,27 @@ Description=TEST-63-ISSUE-17433
 [Service]
 ExecStartPre=rm -f /failed /testok
 Type=oneshot
+
+# Test that a path unit continuously triggering a service that fails condition checks eventually fails with
+# the trigger-limit-hit error.
 ExecStart=rm -f /tmp/nonexistent
 ExecStart=systemctl start test63.path
 ExecStart=touch /tmp/test63
-# Make sure systemd has sufficient time to hit the start limit for test63.service.
+# Make sure systemd has sufficient time to hit the trigger limit for test63.path.
 ExecStart=sleep 2
-ExecStart=sh -x -c 'test "$(systemctl show test63.service --value -p ActiveState)" = failed'
-ExecStart=sh -x -c 'test "$(systemctl show test63.service --value -p Result)" = start-limit-hit'
+ExecStart=sh -x -c 'test "$(systemctl show test63.service --value -p ActiveState)" = inactive'
+ExecStart=sh -x -c 'test "$(systemctl show test63.service --value -p Result)" = success'
 # FIXME: The path remains active, which it should not
 # ExecStart=sh -x -c 'test "$(systemctl show test63.path --value -p ActiveState)" = failed'
-# ExecStart=sh -x -c 'test "$(systemctl show test63.path --value -p Result)" = unit-start-limit-hit'
+# ExecStart=sh -x -c 'test "$(systemctl show test63.path --value -p Result)" = trigger-limit-hit'
+
+# Test that starting the service manually doesn't affect the path unit.
+ExecStart=rm -f /tmp/test63
+ExecStart=systemctl reset-failed
+ExecStart=systemctl start test63.path
+ExecStart=systemctl start test63.service
+ExecStart=sh -x -c 'test "$(systemctl show test63.service --value -p ActiveState)" = inactive'
+ExecStart=sh -x -c 'test "$(systemctl show test63.service --value -p Result)" = success'
+ExecStart=sh -x -c 'test "$(systemctl show test63.path --value -p ActiveState)" = active'
+ExecStart=sh -x -c 'test "$(systemctl show test63.path --value -p Result)" = success'
 ExecStart=sh -x -c 'echo OK >/testok'