basic/cap-list: report empty capability set as ""

$ systemctl show systemd-journald -p CapabilityBoundingSet,AmbientCapabilities
CapabilityBoundingSet=cap_chown cap_dac_override cap_dac_read_search cap_fowner cap_setgid ...
AmbientCapabilities=(null)

↓

$ systemctl show systemd-journald -p CapabilityBoundingSet,AmbientCapabilities
CapabilityBoundingSet=cap_chown cap_dac_override cap_dac_read_search cap_fowner cap_setgid ...
AmbientCapabilities=

Partially fixes #6511. Add some basic tests for the printing function.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/basic/cap-list.c b/src/basic/cap-list.c
index 124641f940..2e9b2d9a55 100644
--- a/src/basic/cap-list.c
+++ b/src/basic/cap-list.c
@@ -86,15 +86,17 @@ int capability_set_to_string_alloc(uint64_t set, char **s) {
 
                         add = strlen(p);
 
-                        if (!GREEDY_REALLOC0(str, allocated, n + add + 2))
+                        if (!GREEDY_REALLOC(str, allocated, n + add + 2))
                                 return -ENOMEM;
 
                         strcpy(mempcpy(str + n, p, add), " ");
                         n += add + 1;
                 }
 
-        if (n != 0)
-                str[n - 1] = '\0';
+        if (!GREEDY_REALLOC(str, allocated, n + 1))
+                return -ENOMEM;
+
+        str[n > 0 ? n - 1 : 0] = '\0'; /* truncate the last space, if it's there */
 
         *s = str;
         str = NULL;