From 598eecf5c1c948535ca626833bc5cea59060913f Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 20 Apr 2022 22:30:22 +0200
Subject: [PATCH] sd-bus: switch to a manual overflow check in
 sd_bus_track_add_name()

This is generally used in a directly client controllable way, hence we
should handle ref count overflow gracefully, instead of hitting an
assert().

As discussed:

https://github.com/systemd/systemd/pull/23099#discussion_r854341850
(cherry picked from commit 7f40cb7c86b0fff3a82096a9499570bad9c19fd2)

[msekleta: We've never switched to using track_item_ref/unref introduced
in c2d7dd35d2 hence we still had potential undefined behavior related to
overflow check and this commit fixes that.]

Related: #2047373
---
 src/libsystemd/sd-bus/bus-track.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/libsystemd/sd-bus/bus-track.c b/src/libsystemd/sd-bus/bus-track.c
index 8893f190a1..b818e93bec 100644
--- a/src/libsystemd/sd-bus/bus-track.c
+++ b/src/libsystemd/sd-bus/bus-track.c
@@ -208,12 +208,16 @@ _public_ int sd_bus_track_add_name(sd_bus_track *track, const char *name) {
         i = hashmap_get(track->names, name);
         if (i) {
                 if (track->recursive) {
-                        unsigned k = i->n_ref + 1;
+                        assert(i->n_ref > 0);
 
-                        if (k < i->n_ref) /* Check for overflow */
+                        /* Manual oveflow check (instead of a DEFINE_TRIVIAL_REF_FUNC() helper or so), so
+                         * that we can return a proper error, given this is almost always called in a
+                         * directly client controllable way, and thus better should never hit an assertion
+                         * here. */
+                        if (i->n_ref >= UINT_MAX)
                                 return -EOVERFLOW;
 
-                        i->n_ref = k;
+                        i->n_ref++;
                 }
 
                 bus_track_remove_from_queue(track);