core: Check unit start rate limiting earlier

Fixes #17433. Currently, if any of the validations we do before we
check start rate limiting fail, we can still enter a busy loop as
no rate limiting gets applied. A common occurence of this scenario
is path units triggering a service that fails a condition check.

To fix the issue, we simply move up start rate limiting checks to
be the first thing we do when starting a unit. To achieve this,
we add a new method to the unit vtable and implement it for the
relevant unit types so that we can do the start rate limit checks
earlier on.

16 files changed, 169 insertions, 43 deletions

diff --git a/src/core/automount.c b/src/core/automount.c
index 30226b9bde..11eb352b9b 100644
--- a/src/core/automount.c
+++ b/src/core/automount.c
@@ -813,12 +813,6 @@ static int automount_start(Unit *u) {
         if (r < 0)
                 return r;
 
-        r = unit_test_start_limit(u);
-        if (r < 0) {
-                automount_enter_dead(a, AUTOMOUNT_FAILURE_START_LIMIT_HIT);
-                return r;
-        }
-
         r = unit_acquire_invocation_id(u);
         if (r < 0)
                 return r;
@@ -1064,6 +1058,21 @@ static bool automount_supported(void) {
         return supported;
 }
 
+static int automount_test_start_limit(Unit *u) {
+        Automount *a = AUTOMOUNT(u);
+        int r;
+
+        assert(a);
+
+        r = unit_test_start_limit(u);
+        if (r < 0) {
+                automount_enter_dead(a, AUTOMOUNT_FAILURE_START_LIMIT_HIT);
+                return r;
+        }
+
+        return 0;
+}
+
 static const char* const automount_result_table[_AUTOMOUNT_RESULT_MAX] = {
         [AUTOMOUNT_SUCCESS]                       = "success",
         [AUTOMOUNT_FAILURE_RESOURCES]             = "resources",
@@ -1126,4 +1135,6 @@ const UnitVTable automount_vtable = {
                         [JOB_FAILED]     = "Failed to unset automount %s.",
                 },
         },
+
+        .test_start_limit = automount_test_start_limit,
 };
diff --git a/src/core/mount.c b/src/core/mount.c
index fb8f72e257..35b56426d4 100644
--- a/src/core/mount.c
+++ b/src/core/mount.c
@@ -1167,12 +1167,6 @@ static int mount_start(Unit *u) {
 
         assert(IN_SET(m->state, MOUNT_DEAD, MOUNT_FAILED));
 
-        r = unit_test_start_limit(u);
-        if (r < 0) {
-                mount_enter_dead(m, MOUNT_FAILURE_START_LIMIT_HIT);
-                return r;
-        }
-
         r = unit_acquire_invocation_id(u);
         if (r < 0)
                 return r;
@@ -2138,6 +2132,21 @@ static int mount_can_clean(Unit *u, ExecCleanMask *ret) {
         return exec_context_get_clean_mask(&m->exec_context, ret);
 }
 
+static int mount_test_start_limit(Unit *u) {
+        Mount *m = MOUNT(u);
+        int r;
+
+        assert(m);
+
+        r = unit_test_start_limit(u);
+        if (r < 0) {
+                mount_enter_dead(m, MOUNT_FAILURE_START_LIMIT_HIT);
+                return r;
+        }
+
+        return 0;
+}
+
 static const char* const mount_exec_command_table[_MOUNT_EXEC_COMMAND_MAX] = {
         [MOUNT_EXEC_MOUNT]   = "ExecMount",
         [MOUNT_EXEC_UNMOUNT] = "ExecUnmount",
@@ -2235,4 +2244,6 @@ const UnitVTable mount_vtable = {
                         [JOB_TIMEOUT]    = "Timed out unmounting %s.",
                 },
         },
+
+        .test_start_limit = mount_test_start_limit,
 };
diff --git a/src/core/path.c b/src/core/path.c
index 800524a308..693636b0ee 100644
--- a/src/core/path.c
+++ b/src/core/path.c
@@ -590,12 +590,6 @@ static int path_start(Unit *u) {
         if (r < 0)
                 return r;
 
-        r = unit_test_start_limit(u);
-        if (r < 0) {
-                path_enter_dead(p, PATH_FAILURE_START_LIMIT_HIT);
-                return r;
-        }
-
         r = unit_acquire_invocation_id(u);
         if (r < 0)
                 return r;
@@ -812,6 +806,21 @@ static void path_reset_failed(Unit *u) {
         p->result = PATH_SUCCESS;
 }
 
+static int path_test_start_limit(Unit *u) {
+        Path *p = PATH(u);
+        int r;
+
+        assert(p);
+
+        r = unit_test_start_limit(u);
+        if (r < 0) {
+                path_enter_dead(p, PATH_FAILURE_START_LIMIT_HIT);
+                return r;
+        }
+
+        return 0;
+}
+
 static const char* const path_type_table[_PATH_TYPE_MAX] = {
         [PATH_EXISTS]              = "PathExists",
         [PATH_EXISTS_GLOB]         = "PathExistsGlob",
@@ -866,4 +875,6 @@ const UnitVTable path_vtable = {
         .reset_failed = path_reset_failed,
 
         .bus_set_property = bus_path_set_property,
+
+        .test_start_limit = path_test_start_limit,
 };
diff --git a/src/core/service.c b/src/core/service.c
index c55304d170..9d8eef1f74 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -2436,13 +2436,6 @@ static int service_start(Unit *u) {
 
         assert(IN_SET(s->state, SERVICE_DEAD, SERVICE_FAILED));
 
-        /* Make sure we don't enter a busy loop of some kind. */
-        r = unit_test_start_limit(u);
-        if (r < 0) {
-                service_enter_dead(s, SERVICE_FAILURE_START_LIMIT_HIT, false);
-                return r;
-        }
-
         r = unit_acquire_invocation_id(u);
         if (r < 0)
                 return r;
@@ -4445,6 +4438,22 @@ static const char *service_finished_job(Unit *u, JobType t, JobResult result) {
         return NULL;
 }
 
+static int service_test_start_limit(Unit *u) {
+        Service *s = SERVICE(u);
+        int r;
+
+        assert(s);
+
+        /* Make sure we don't enter a busy loop of some kind. */
+        r = unit_test_start_limit(u);
+        if (r < 0) {
+                service_enter_dead(s, SERVICE_FAILURE_START_LIMIT_HIT, false);
+                return r;
+        }
+
+        return 0;
+}
+
 static const char* const service_restart_table[_SERVICE_RESTART_MAX] = {
         [SERVICE_RESTART_NO]          = "no",
         [SERVICE_RESTART_ON_SUCCESS]  = "on-success",
@@ -4608,4 +4617,6 @@ const UnitVTable service_vtable = {
                 },
                 .finished_job = service_finished_job,
         },
+
+        .test_start_limit = service_test_start_limit,
 };
diff --git a/src/core/socket.c b/src/core/socket.c
index ceaf39bdd3..177068eed4 100644
--- a/src/core/socket.c
+++ b/src/core/socket.c
@@ -2513,12 +2513,6 @@ static int socket_start(Unit *u) {
 
         assert(IN_SET(s->state, SOCKET_DEAD, SOCKET_FAILED));
 
-        r = unit_test_start_limit(u);
-        if (r < 0) {
-                socket_enter_dead(s, SOCKET_FAILURE_START_LIMIT_HIT);
-                return r;
-        }
-
         r = unit_acquire_invocation_id(u);
         if (r < 0)
                 return r;
@@ -3425,6 +3419,21 @@ static int socket_can_clean(Unit *u, ExecCleanMask *ret) {
         return exec_context_get_clean_mask(&s->exec_context, ret);
 }
 
+static int socket_test_start_limit(Unit *u) {
+        Socket *s = SOCKET(u);
+        int r;
+
+        assert(s);
+
+        r = unit_test_start_limit(u);
+        if (r < 0) {
+                socket_enter_dead(s, SOCKET_FAILURE_START_LIMIT_HIT);
+                return r;
+        }
+
+        return 0;
+}
+
 static const char* const socket_exec_command_table[_SOCKET_EXEC_COMMAND_MAX] = {
         [SOCKET_EXEC_START_PRE]   = "ExecStartPre",
         [SOCKET_EXEC_START_CHOWN] = "ExecStartChown",
@@ -3551,4 +3560,6 @@ const UnitVTable socket_vtable = {
                         [JOB_TIMEOUT]    = "Timed out stopping %s.",
                 },
         },
+
+        .test_start_limit = socket_test_start_limit,
 };
diff --git a/src/core/swap.c b/src/core/swap.c
index 48ba5c7664..29c63118ac 100644
--- a/src/core/swap.c
+++ b/src/core/swap.c
@@ -932,12 +932,6 @@ static int swap_start(Unit *u) {
                 if (UNIT(other)->job && UNIT(other)->job->state == JOB_RUNNING)
                         return -EAGAIN;
 
-        r = unit_test_start_limit(u);
-        if (r < 0) {
-                swap_enter_dead(s, SWAP_FAILURE_START_LIMIT_HIT);
-                return r;
-        }
-
         r = unit_acquire_invocation_id(u);
         if (r < 0)
                 return r;
@@ -1588,6 +1582,21 @@ static int swap_can_clean(Unit *u, ExecCleanMask *ret) {
         return exec_context_get_clean_mask(&s->exec_context, ret);
 }
 
+static int swap_test_start_limit(Unit *u) {
+        Swap *s = SWAP(u);
+        int r;
+
+        assert(s);
+
+        r = unit_test_start_limit(u);
+        if (r < 0) {
+                swap_enter_dead(s, SWAP_FAILURE_START_LIMIT_HIT);
+                return r;
+        }
+
+        return 0;
+}
+
 static const char* const swap_exec_command_table[_SWAP_EXEC_COMMAND_MAX] = {
         [SWAP_EXEC_ACTIVATE]   = "ExecActivate",
         [SWAP_EXEC_DEACTIVATE] = "ExecDeactivate",
@@ -1683,4 +1692,6 @@ const UnitVTable swap_vtable = {
                         [JOB_TIMEOUT]    = "Timed out deactivating swap %s.",
                 },
         },
+
+        .test_start_limit = swap_test_start_limit,
 };
diff --git a/src/core/timer.c b/src/core/timer.c
index 12515a6a75..8853121c00 100644
--- a/src/core/timer.c
+++ b/src/core/timer.c
@@ -627,12 +627,6 @@ static int timer_start(Unit *u) {
         if (r < 0)
                 return r;
 
-        r = unit_test_start_limit(u);
-        if (r < 0) {
-                timer_enter_dead(t, TIMER_FAILURE_START_LIMIT_HIT);
-                return r;
-        }
-
         r = unit_acquire_invocation_id(u);
         if (r < 0)
                 return r;
@@ -890,6 +884,21 @@ static int timer_can_clean(Unit *u, ExecCleanMask *ret) {
         return 0;
 }
 
+static int timer_test_start_limit(Unit *u) {
+        Timer *t = TIMER(u);
+        int r;
+
+        assert(t);
+
+        r = unit_test_start_limit(u);
+        if (r < 0) {
+                timer_enter_dead(t, TIMER_FAILURE_START_LIMIT_HIT);
+                return r;
+        }
+
+        return 0;
+}
+
 static const char* const timer_base_table[_TIMER_BASE_MAX] = {
         [TIMER_ACTIVE]        = "OnActiveSec",
         [TIMER_BOOT]          = "OnBootSec",
@@ -949,4 +958,6 @@ const UnitVTable timer_vtable = {
         .timezone_change = timer_timezone_change,
 
         .bus_set_property = bus_timer_set_property,
+
+        .test_start_limit = timer_test_start_limit,
 };
diff --git a/src/core/unit.c b/src/core/unit.c
index 7d72dfa864..48e7b95e56 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -1857,6 +1857,13 @@ int unit_start(Unit *u) {
 
         assert(u);
 
+        /* Check start rate limiting early so that failure conditions don't cause us to enter a busy loop. */
+        if (UNIT_VTABLE(u)->test_start_limit) {
+                int r = UNIT_VTABLE(u)->test_start_limit(u);
+                if (r < 0)
+                        return r;
+        }
+
         /* If this is already started, then this will succeed. Note that this will even succeed if this unit
          * is not startable by the user. This is relied on to detect when we need to wait for units and when
          * waiting is finished. */
diff --git a/src/core/unit.h b/src/core/unit.h
index b3e9c2106f..b689f29f8f 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -658,6 +658,10 @@ typedef struct UnitVTable {
          * of this type will immediately fail. */
         bool (*supported)(void);
 
+        /* If this function is set, it's invoked first as part of starting a unit to allow start rate
+         * limiting checks to occur before we do anything else. */
+        int (*test_start_limit)(Unit *u);
+
         /* The strings to print in status messages */
         UnitStatusMessageFormats status_message_formats;
 
diff --git a/test/TEST-63-ISSUE-17433/Makefile b/test/TEST-63-ISSUE-17433/Makefile
new file mode 120000
index 0000000000..e9f93b1104
--- /dev/null
+++ b/test/TEST-63-ISSUE-17433/Makefile
@@ -0,0 +1 @@
+../TEST-01-BASIC/Makefile
\ No newline at end of file
diff --git a/test/TEST-63-ISSUE-17433/test.sh b/test/TEST-63-ISSUE-17433/test.sh
new file mode 100755
index 0000000000..c595a9f2de
--- /dev/null
+++ b/test/TEST-63-ISSUE-17433/test.sh
@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+set -e
+
+TEST_DESCRIPTION="https://github.com/systemd/systemd/issues/17433"
+
+# shellcheck source=test/test-functions
+. "${TEST_BASE_DIR:?}/test-functions"
+
+do_test "$@"
diff --git a/test/meson.build b/test/meson.build
index a21230a4a8..b8335fb50f 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -33,6 +33,8 @@ if install_tests
                        install_dir : testdata_dir)
         install_subdir('testsuite-52.units',
                        install_dir : testdata_dir)
+        install_subdir('testsuite-63.units',
+                       install_dir : testdata_dir)
 
         testsuite08_dir = testdata_dir + '/testsuite-08.units'
         install_data('testsuite-08.units/-.mount',
diff --git a/test/testsuite-10.units/test10.service b/test/testsuite-10.units/test10.service
index d0be786b01..2fb476b986 100644
--- a/test/testsuite-10.units/test10.service
+++ b/test/testsuite-10.units/test10.service
@@ -1,6 +1,9 @@
 [Unit]
 Requires=test10.socket
 ConditionPathExistsGlob=/tmp/nonexistent
+# Make sure we hit the socket trigger limit in the test and not the service start limit.
+StartLimitInterval=1000
+StartLimitBurst=1000
 
 [Service]
 ExecStart=true
diff --git a/test/testsuite-63.units/test63.path b/test/testsuite-63.units/test63.path
new file mode 100644
index 0000000000..a6573bda0a
--- /dev/null
+++ b/test/testsuite-63.units/test63.path
@@ -0,0 +1,2 @@
+[Path]
+PathExists=/tmp/test63
diff --git a/test/testsuite-63.units/test63.service b/test/testsuite-63.units/test63.service
new file mode 100644
index 0000000000..c83801874d
--- /dev/null
+++ b/test/testsuite-63.units/test63.service
@@ -0,0 +1,5 @@
+[Unit]
+ConditionPathExists=!/tmp/nonexistent
+
+[Service]
+ExecStart=true
diff --git a/test/units/testsuite-63.service b/test/units/testsuite-63.service
new file mode 100644
index 0000000000..04122723d4
--- /dev/null
+++ b/test/units/testsuite-63.service
@@ -0,0 +1,16 @@
+[Unit]
+Description=TEST-63-ISSUE-17433
+
+[Service]
+ExecStartPre=rm -f /failed /testok
+Type=oneshot
+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.
+ExecStart=sleep 2
+ExecStart=sh -x -c 'test "$(systemctl show test63.service -P ActiveState)" = failed'
+ExecStart=sh -x -c 'test "$(systemctl show test63.service -P Result)" = start-limit-hit'
+ExecStart=sh -x -c 'test "$(systemctl show test63.path -P ActiveState)" = failed'
+ExecStart=sh -x -c 'test "$(systemctl show test63.path -P Result)" = unit-start-limit-hit'
+ExecStart=sh -x -c 'echo OK >/testok'