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From 441684c6c961edec1391562fb2f48ff997a6169e Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Mon, 23 Nov 2020 15:38:00 +0100
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Subject: [PATCH] sd-event: ref event loop while in sd_event_prepare() ot
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sd_event_run()
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sd_event_prepare() invokes callbacks that might drop the last user ref
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on our event loop. Let's make sure we keep an explicit ref around it, so
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that we won't end up with an invalid pointer. Similar in sd_event_run().
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Basically, any function that is publically callable that might end up
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invoking callbacks should ref the relevant objects to be protected
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against callbacks destroying these objects while we still want to access
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them. We did this correctly in sd_event_dispatch() and sd_event_loop(),
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but these are not the only ones which are callable from the outside.
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(cherry picked from commit f814c871e65df8552a055dd887bc94b074037833)
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Related: #1819868
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---
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src/libsystemd/sd-event/sd-event.c | 15 +++++++++------
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1 file changed, 9 insertions(+), 6 deletions(-)
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diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
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index 537a0b81d4..be1e6e5f53 100644
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--- a/src/libsystemd/sd-event/sd-event.c
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+++ b/src/libsystemd/sd-event/sd-event.c
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@@ -3256,7 +3256,6 @@ static int event_prepare(sd_event *e) {
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static int dispatch_exit(sd_event *e) {
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sd_event_source *p;
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- _cleanup_(sd_event_unrefp) sd_event *ref = NULL;
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int r;
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assert(e);
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@@ -3267,7 +3266,7 @@ static int dispatch_exit(sd_event *e) {
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return 0;
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}
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- ref = sd_event_ref(e);
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+ _unused_ _cleanup_(sd_event_unrefp) sd_event *ref = sd_event_ref(e);
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e->iteration++;
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e->state = SD_EVENT_EXITING;
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r = source_dispatch(p);
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@@ -3365,6 +3364,9 @@ _public_ int sd_event_prepare(sd_event *e) {
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* syscalls */
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assert_return(!e->default_event_ptr || e->tid == gettid(), -EREMOTEIO);
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+ /* Make sure that none of the preparation callbacks ends up freeing the event source under our feet */
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+ _unused_ _cleanup_(sd_event_unrefp) sd_event *ref = sd_event_ref(e);
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+
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if (e->exit_requested)
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goto pending;
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@@ -3549,9 +3551,8 @@ _public_ int sd_event_dispatch(sd_event *e) {
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p = event_next_pending(e);
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if (p) {
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- _cleanup_(sd_event_unrefp) sd_event *ref = NULL;
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+ _unused_ _cleanup_(sd_event_unrefp) sd_event *ref = sd_event_ref(e);
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- ref = sd_event_ref(e);
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e->state = SD_EVENT_RUNNING;
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r = source_dispatch(p);
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e->state = SD_EVENT_INITIAL;
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@@ -3600,6 +3601,9 @@ _public_ int sd_event_run(sd_event *e, uint64_t timeout) {
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}
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}
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+ /* Make sure that none of the preparation callbacks ends up freeing the event source under our feet */
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+ _unused_ _cleanup_(sd_event_unrefp) sd_event *ref = sd_event_ref(e);
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+
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r = sd_event_prepare(e);
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if (r == 0)
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/* There was nothing? Then wait... */
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@@ -3621,7 +3625,6 @@ _public_ int sd_event_run(sd_event *e, uint64_t timeout) {
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}
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_public_ int sd_event_loop(sd_event *e) {
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- _cleanup_(sd_event_unrefp) sd_event *ref = NULL;
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int r;
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assert_return(e, -EINVAL);
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@@ -3629,7 +3632,7 @@ _public_ int sd_event_loop(sd_event *e) {
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assert_return(!event_pid_changed(e), -ECHILD);
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assert_return(e->state == SD_EVENT_INITIAL, -EBUSY);
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- ref = sd_event_ref(e);
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+ _unused_ _cleanup_(sd_event_unrefp) sd_event *ref = NULL;
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while (e->state != SD_EVENT_FINISHED) {
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r = sd_event_run(e, (uint64_t) -1);
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