tmpfiles: fix crash with NULL in arg_root and other fixes and tests

The function to replacement paths into the configuration file list was borked.
Apart from the crash with empty root prefix, it would incorrectly handle the
case where root *was* set, and the replacement file was supposed to override
an existing file.

prefix_root is used instead of path_join because prefix_root removes duplicate
slashes (when --root=dir/ is used).

A test is added.

Fixes #11124.

2 files changed, 73 insertions, 9 deletions

diff --git a/src/basic/conf-files.c b/src/basic/conf-files.c
index 76750606b..b70c6e50a 100644
--- a/src/basic/conf-files.c
+++ b/src/basic/conf-files.c
@@ -201,14 +201,17 @@ int conf_files_insert(char ***strv, const char *root, char **dirs, const char *p
                 if (c == 0) {
                         char **dir;
 
-                        /* Oh, we found our spot and it already contains something. */
+                        /* Oh, there already is an entry with a matching name (the last component). */
+
                         STRV_FOREACH(dir, dirs) {
+                                _cleanup_free_ char *rdir = NULL;
                                 char *p1, *p2;
 
-                                p1 = path_startswith((*strv)[i], root);
-                                if (p1)
-                                        /* Skip "/" in *dir, because p1 is without "/" too */
-                                        p1 = path_startswith(p1, *dir + 1);
+                                rdir = prefix_root(root, *dir);
+                                if (!rdir)
+                                        return -ENOMEM;
+
+                                p1 = path_startswith((*strv)[i], rdir);
                                 if (p1)
                                         /* Existing entry with higher priority
                                          * or same priority, no need to do anything. */
@@ -217,7 +220,8 @@ int conf_files_insert(char ***strv, const char *root, char **dirs, const char *p
                                 p2 = path_startswith(path, *dir);
                                 if (p2) {
                                         /* Our new entry has higher priority */
-                                        t = path_join(root, path);
+
+                                        t = prefix_root(root, path);
                                         if (!t)
                                                 return log_oom();
 
@@ -233,7 +237,8 @@ int conf_files_insert(char ***strv, const char *root, char **dirs, const char *p
                 /* … we are not there yet, let's continue */
         }
 
-        t = path_join(root, path);
+        /* The new file has lower priority than all the existing entries */
+        t = prefix_root(root, path);
         if (!t)
                 return -ENOMEM;
 
@@ -308,7 +313,7 @@ int conf_files_list_with_replacement(
                 if (r < 0)
                         return log_error_errno(r, "Failed to extend config file list: %m");
 
-                p = path_join(root, replacement);
+                p = prefix_root(root, replacement);
                 if (!p)
                         return log_oom();
         }
diff --git a/src/test/test-conf-files.c b/src/test/test-conf-files.c
index b69046c9c..9fd8b6b59 100644
--- a/src/test/test-conf-files.c
+++ b/src/test/test-conf-files.c
@@ -13,6 +13,7 @@
 #include "macro.h"
 #include "mkdir.h"
 #include "parse-util.h"
+#include "path-util.h"
 #include "rm-rf.h"
 #include "string-util.h"
 #include "strv.h"
@@ -43,7 +44,7 @@ static void test_conf_files_list(bool use_root) {
         _cleanup_strv_free_ char **found_files = NULL, **found_files2 = NULL;
         const char *root_dir, *search_1, *search_2, *expect_a, *expect_b, *expect_c, *mask;
 
-        log_debug("/* %s */", __func__);
+        log_debug("/* %s(%s) */", __func__, yes_no(use_root));
 
         setup_test_dir(tmp_dir,
                        "/dir1/a.conf",
@@ -93,10 +94,68 @@ static void test_conf_files_list(bool use_root) {
         assert_se(rm_rf(tmp_dir, REMOVE_ROOT|REMOVE_PHYSICAL) == 0);
 }
 
+static void test_conf_files_insert(const char *root) {
+        _cleanup_strv_free_ char **s = NULL;
+
+        log_info("/* %s root=%s */", __func__, strempty(root));
+
+        char **dirs = STRV_MAKE("/dir1", "/dir2", "/dir3");
+
+        _cleanup_free_ const char
+                *foo1 = prefix_root(root, "/dir1/foo.conf"),
+                *foo2 = prefix_root(root, "/dir2/foo.conf"),
+                *bar2 = prefix_root(root, "/dir2/bar.conf"),
+                *zzz3 = prefix_root(root, "/dir3/zzz.conf"),
+                *whatever = prefix_root(root, "/whatever.conf");
+
+        assert_se(conf_files_insert(&s, root, dirs, "/dir2/foo.conf") == 0);
+        assert_se(strv_equal(s, STRV_MAKE(foo2)));
+
+        /* The same file again, https://github.com/systemd/systemd/issues/11124 */
+        assert_se(conf_files_insert(&s, root, dirs, "/dir2/foo.conf") == 0);
+        assert_se(strv_equal(s, STRV_MAKE(foo2)));
+
+        /* Lower priority → new entry is ignored */
+        assert_se(conf_files_insert(&s, root, dirs, "/dir3/foo.conf") == 0);
+        assert_se(strv_equal(s, STRV_MAKE(foo2)));
+
+        /* Higher priority → new entry replaces */
+        assert_se(conf_files_insert(&s, root, dirs, "/dir1/foo.conf") == 0);
+        assert_se(strv_equal(s, STRV_MAKE(foo1)));
+
+        /* Earlier basename */
+        assert_se(conf_files_insert(&s, root, dirs, "/dir2/bar.conf") == 0);
+        assert_se(strv_equal(s, STRV_MAKE(bar2, foo1)));
+
+        /* Later basename */
+        assert_se(conf_files_insert(&s, root, dirs, "/dir3/zzz.conf") == 0);
+        assert_se(strv_equal(s, STRV_MAKE(bar2, foo1, zzz3)));
+
+        /* All lower priority → all ignored */
+        assert_se(conf_files_insert(&s, root, dirs, "/dir3/zzz.conf") == 0);
+        assert_se(conf_files_insert(&s, root, dirs, "/dir2/bar.conf") == 0);
+        assert_se(conf_files_insert(&s, root, dirs, "/dir3/bar.conf") == 0);
+        assert_se(conf_files_insert(&s, root, dirs, "/dir2/foo.conf") == 0);
+        assert_se(strv_equal(s, STRV_MAKE(bar2, foo1, zzz3)));
+
+        /* Two entries that don't match any of the directories, but match basename */
+        assert_se(conf_files_insert(&s, root, dirs, "/dir4/zzz.conf") == 0);
+        assert_se(conf_files_insert(&s, root, dirs, "/zzz.conf") == 0);
+        assert_se(strv_equal(s, STRV_MAKE(bar2, foo1, zzz3)));
+
+        /* An entry that doesn't match any of the directories, no match at all */
+        assert_se(conf_files_insert(&s, root, dirs, "/whatever.conf") == 0);
+        assert_se(strv_equal(s, STRV_MAKE(bar2, foo1, whatever, zzz3)));
+}
+
 int main(int argc, char **argv) {
         test_setup_logging(LOG_DEBUG);
 
         test_conf_files_list(false);
         test_conf_files_list(true);
+        test_conf_files_insert(NULL);
+        test_conf_files_insert("/root");
+        test_conf_files_insert("/root/");
+
         return 0;
 }