systemd/0001-conf-parser-introduce-early-drop-ins.patch

From 569f94a86a608fa7a47fef583f3f504ec8223967 Mon Sep 17 00:00:00 2001
From: Franck Bui <fbui@suse.com>
Date: Fri, 22 Jan 2021 14:57:08 +0100
Subject: [PATCH 1/1] conf-parser: introduce 'early' drop-ins
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As formerly known as "downstream conf file drop-ins should never override main
user conf file".

Previously all drop-ins, including those shipped by downstream, shipped in
/usr, could override user's main configuration file (located in /etc) because
the main file was always parsed first.

This was problematic for downstreams because their customization should never
override the users one in general. Therefore the only way to make this logic
usable was by teaching users to never use the main conf files and to put all
theirs settings in drop-ins with a higher priority than the one downsteam would
use. However customizing the defaults through the main conf file is something
very well established since a long time hence this is not something
conceivable.

This patch reworks the way we parse configuration files by introducing "early"
conf files (idea from Zbigniew Jędrzejewski-Szmek), which always have a
priority lower than the main config file and hence other conf file drop-ins
too.

Early conf files can be located in any locations where regular conf snippets
can be installed and are sorted between them using the same sorting rules that
apply to other conf files. A conf file is considered as an early one if its
filename is prefixed with "__" (double underscore).

Hence for example, drop-in "/usr/lib/systemd/logind.conf.d/__99-foo.conf" will
always be parsed before:

  /etc/systemd/logind.conf
  /etc/systemd/logind.conf.d/00-foo.conf
  /usr/lib/systemd/logind.conf.d/00-foo.conf

This change isn't backwards-compatible, but the '__' prefix is something that
is unlikely used. Hence the risk should be very low.

Unfortunately upstream is not seing this problem as a serious one and accept
that vendors' configuration files can take precedence over the main
configuration files (placed in /etc). See the following links for the
related discussions:

  https://github.com/systemd/systemd/issues/2121 (initial issue report)
  https://github.com/systemd/systemd/pull/17161  (first attempt to solve this issue)
  https://github.com/systemd/systemd/pull/18347  (introduction of early drop-in)

Since SUSE heavily relies on drop-ins to customize some of the upstream default
settings, there was no other choice than to diverge from upstream in this
regard.

But it should be noted that these early drop-ins are strictly reserved for SUSE
own purpose only. IOW users should never use them and early drop-ins should
never be created in /etc but only in /usr. We reserve the right to change or
drop this feature at any time.

Fixes: #2121
---
 src/shared/conf-parser.c    |  47 ++++++++++-
 src/test/test-conf-parser.c | 151 ++++++++++++++++++++++++++++++++++++
 2 files changed, 194 insertions(+), 4 deletions(-)

diff --git a/src/shared/conf-parser.c b/src/shared/conf-parser.c
index 7499b3b882..799026626c 100644
--- a/src/shared/conf-parser.c
+++ b/src/shared/conf-parser.c
@@ -426,6 +426,7 @@ int config_parse(const char *unit,
 
 static int config_parse_many_files(
                 const char *conf_file,
+                char **early_files,
                 char **files,
                 const char *sections,
                 ConfigItemLookup lookup,
@@ -438,6 +439,12 @@ static int config_parse_many_files(
         char **fn;
         int r;
 
+        STRV_FOREACH(fn, early_files) {
+                r = config_parse(NULL, *fn, NULL, sections, lookup, table, flags, userdata, &mtime);
+                if (r < 0)
+                        return r;
+        }
+
         if (conf_file) {
                 r = config_parse(NULL, conf_file, NULL, sections, lookup, table, flags, userdata, &mtime);
                 if (r < 0)
@@ -456,6 +463,28 @@ static int config_parse_many_files(
         return 0;
 }
 
+static int config_parse_split_conf_files(char **files, char ***early_files, char ***late_files) {
+        char **f;
+
+        assert(files);
+        assert(early_files);
+        assert(late_files);
+
+        STRV_FOREACH(f, files) {
+                char ***s, *p;
+
+                p = strdup(*f);
+                if (!p)
+                        return log_oom();
+
+                s = startswith(basename(*f), "__") ? early_files : late_files;
+                if (strv_push(s, p) < 0)
+                        return log_oom();
+        }
+
+        return 0;
+}
+
 /* Parse each config file in the directories specified as nulstr. */
 int config_parse_many_nulstr(
                 const char *conf_file,
@@ -467,14 +496,19 @@ int config_parse_many_nulstr(
                 void *userdata,
                 usec_t *ret_mtime) {
 
-        _cleanup_strv_free_ char **files = NULL;
+        _cleanup_strv_free_ char **files = NULL, **early_files = NULL, **late_files = NULL;
         int r;
 
         r = conf_files_list_nulstr(&files, ".conf", NULL, 0, conf_file_dirs);
         if (r < 0)
                 return r;
 
-        return config_parse_many_files(conf_file, files, sections, lookup, table, flags, userdata, ret_mtime);
+        r = config_parse_split_conf_files(files, &early_files, &late_files);
+        if (r < 0)
+                return r;
+
+        return config_parse_many_files(conf_file, early_files, late_files, sections,
+                                       lookup, table, flags, userdata, ret_mtime);
 }
 
 /* Parse each config file in the directories specified as strv. */
@@ -489,8 +523,8 @@ int config_parse_many(
                 void *userdata,
                 usec_t *ret_mtime) {
 
+        _cleanup_strv_free_ char **files = NULL, **early_files = NULL, **late_files = NULL;
         _cleanup_strv_free_ char **dropin_dirs = NULL;
-        _cleanup_strv_free_ char **files = NULL;
         const char *suffix;
         int r;
 
@@ -503,7 +537,12 @@ int config_parse_many(
         if (r < 0)
                 return r;
 
-        return config_parse_many_files(conf_file, files, sections, lookup, table, flags, userdata, ret_mtime);
+        r = config_parse_split_conf_files(files, &early_files, &late_files);
+        if (r < 0)
+                return r;
+
+        return config_parse_many_files(conf_file, early_files, late_files, sections,
+                                       lookup, table, flags, userdata, ret_mtime);
 }
 
 #define DEFINE_PARSER(type, vartype, conv_func)                         \
diff --git a/src/test/test-conf-parser.c b/src/test/test-conf-parser.c
index 07edc17f92..2df4b073c5 100644
--- a/src/test/test-conf-parser.c
+++ b/src/test/test-conf-parser.c
@@ -5,6 +5,9 @@
 #include "fs-util.h"
 #include "log.h"
 #include "macro.h"
+#include "mkdir.h"
+#include "path-util.h"
+#include "rm-rf.h"
 #include "string-util.h"
 #include "strv.h"
 #include "tmpfile-util.h"
@@ -385,6 +388,151 @@ static void test_config_parse(unsigned i, const char *s) {
         }
 }
 
+static void setup_conf_files(const char *root, bool is_main, char **conf_files, char ***ret_conf_dirs) {
+        char **path;
+
+        /* If 'is_main' is true then 'conf_files' should only contain an entry
+         * for the main conf file. */
+        if (is_main)
+                assert_se(strv_length(conf_files) <= 1);
+
+        STRV_FOREACH(path, conf_files) {
+                _cleanup_free_ char *abspath = NULL;
+                _cleanup_fclose_ FILE *f = NULL;
+
+                abspath = path_join(root, *path);
+                assert_se(abspath);
+
+                (void) mkdir_parents(abspath, 0755);
+
+                f = fopen(abspath, "w");
+                assert_se(f);
+                fprintf(f,
+                        "[Section]\n"
+                        "name=%s\n",
+                        *path);
+
+                if (!is_main)
+                        fprintf(f,
+                                "%s=%s\n",
+                                startswith(basename(*path), "__") ? "early" : "late",
+                                *path);
+
+                if (ret_conf_dirs) {
+                        char *d;
+
+                        assert_se((d = dirname_malloc(abspath)));
+                        assert_se(strv_push(ret_conf_dirs, d) == 0);
+                }
+        }
+
+        if (ret_conf_dirs) {
+                strv_uniq(*ret_conf_dirs);
+                strv_sort(*ret_conf_dirs);
+        }
+}
+
+static void test_config_parse_many_one(bool nulstr, const char *main, char **conf_files,
+                                       const char *name, const char *early, const char *late) {
+
+        _cleanup_free_ char *parsed_name = NULL, *parsed_early = NULL, *parsed_late = NULL;
+        _cleanup_strv_free_ char **conf_dirs = NULL;
+        _cleanup_free_ char *conf_dirs_nulstr = NULL;
+        char *conf_file;
+        char *tmp_dir;
+        size_t size;
+        int r;
+
+        const ConfigTableItem items[] = {
+                { "Section", "name",  config_parse_string, 0, &parsed_name},
+                { "Section", "late",  config_parse_string, 0, &parsed_late},
+                { "Section", "early", config_parse_string, 0, &parsed_early},
+        };
+
+        tmp_dir = strdupa("/tmp/test-conf-parser-XXXXXX");
+        assert_se(mkdtemp(tmp_dir));
+
+        setup_conf_files(tmp_dir, true, STRV_MAKE(main), NULL);
+        setup_conf_files(tmp_dir, false, conf_files, &conf_dirs);
+
+        conf_file = main ? strjoina(tmp_dir, "/", main) : NULL;
+
+        if (nulstr) {
+                r = strv_make_nulstr(conf_dirs, &conf_dirs_nulstr, &size);
+                assert_se(r == 0);
+
+                r = config_parse_many_nulstr(conf_file, conf_dirs_nulstr,
+                                             "Section\0",
+                                             config_item_table_lookup, items,
+                                             CONFIG_PARSE_WARN,
+                                             NULL,
+                                             NULL);
+        } else {
+                r = config_parse_many(conf_file, (const char * const*) conf_dirs, "",
+                                      "Section\0",
+                                      config_item_table_lookup, items,
+                                      CONFIG_PARSE_WARN,
+                                      NULL,
+                                      NULL);
+        }
+
+        assert_se(r == 0);
+        assert_se((!name && !parsed_name) || streq(name, parsed_name));
+        assert_se((!late && !parsed_late) || streq(late, parsed_late));
+        assert_se((!early && !parsed_early) || streq(early, parsed_early));
+
+        assert_se(rm_rf(tmp_dir, REMOVE_ROOT|REMOVE_PHYSICAL) == 0);
+}
+
+static void test_config_parse_many(bool nulstr) {
+        log_info("== %s%s ==", __func__, nulstr ? "_nulstr" : "");
+
+        test_config_parse_many_one(nulstr, NULL, NULL, NULL, NULL, NULL);
+
+        test_config_parse_many_one(nulstr,
+                                   "dir/main.conf", NULL,
+                                   "dir/main.conf", NULL, NULL);
+
+        test_config_parse_many_one(nulstr,
+                                   NULL, STRV_MAKE("dir1/50-foo.conf"),
+                                   "dir1/50-foo.conf", NULL, "dir1/50-foo.conf");
+
+        test_config_parse_many_one(nulstr,
+                                   NULL, STRV_MAKE("dir1/__50-foo.conf"),
+                                   "dir1/__50-foo.conf", "dir1/__50-foo.conf", NULL);
+
+        test_config_parse_many_one(nulstr,
+                                   NULL, STRV_MAKE("dir1/10-foo.conf", "dir1/50-bar.conf"),
+                                   "dir1/50-bar.conf", NULL, "dir1/50-bar.conf");
+
+        test_config_parse_many_one(nulstr,
+                                   NULL, STRV_MAKE("dir1/50-foo.conf", "dir2/10-bar.conf"),
+                                   "dir1/50-foo.conf", NULL, "dir1/50-foo.conf");
+
+        test_config_parse_many_one(nulstr,
+                                   NULL, STRV_MAKE("dir1/10-foo.conf", "dir2/10-foo.conf"),
+                                   "dir1/10-foo.conf", NULL, "dir1/10-foo.conf");
+
+        /* Early conf files should never override the main one whatever their
+         * priority/location. */
+        test_config_parse_many_one(nulstr,
+                                   "dir/10-main.conf",
+                                   STRV_MAKE("dir1/__10-foo.conf", "dir2/__99-foo.conf"),
+                                   "dir/10-main.conf", "dir2/__99-foo.conf", NULL);
+
+        /* Late conf files always take precendence over the early conf files
+         * and the main one. */
+        test_config_parse_many_one(nulstr,
+                                   "dir/50-main.conf", STRV_MAKE("dir1/10-foo.conf"),
+                                   "dir1/10-foo.conf", NULL, "dir1/10-foo.conf");
+
+        test_config_parse_many_one(nulstr,
+                                   "dir/10-main.conf",
+                                   STRV_MAKE("dir1/__10-foo.conf", "dir2/__99-foo.conf",
+                                             "dir2/10-foo.conf"),
+                                   "dir2/10-foo.conf", "dir2/__99-foo.conf", "dir2/10-foo.conf");
+}
+
 int main(int argc, char **argv) {
         unsigned i;
 
@@ -407,5 +555,8 @@ int main(int argc, char **argv) {
         for (i = 0; i < ELEMENTSOF(config_file); i++)
                 test_config_parse(i, config_file[i]);
 
+        test_config_parse_many(true);
+        test_config_parse_many(false);
+
         return 0;
 }
-- 
2.26.2