core: add %d specifier for the $CREDENTIALS_DIRECTORY

Resolves: #22549

man/systemd.unit.xml

@@ -1975,6 +1975,11 @@
             <entry>Cache directory root</entry>
             <entry>This is either <filename>/var/cache</filename> (for the system manager) or the path <literal>$XDG_CACHE_HOME</literal> resolves to (for user managers).</entry>
           </row>
+          <row>
+            <entry><literal>%d</literal></entry>
+            <entry>Credentials directory</entry>
+            <entry>This is the value of the <literal>$CREDENTIALS_DIRECTORY</literal> environment variable if available. See section "Credentials" in <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information.</entry>
+          </row>
           <row>
             <entry><literal>%E</literal></entry>
             <entry>Configuration directory root</entry>

src/core/unit-printf.c

@@ -148,6 +148,20 @@ static int specifier_special_directory(char specifier, const void *data, const c
         return 0;
 }
 
+static int specifier_credentials_dir(char specifier, const void *data, const char *root, const void *userdata, char **ret) {
+        const Unit *u = ASSERT_PTR(userdata);
+        char *d;
+
+        assert(ret);
+
+        d = strjoin(u->manager->prefix[EXEC_DIRECTORY_RUNTIME], "/credentials/", u->id);
+        if (!d)
+                return -ENOMEM;
+
+        *ret = d;
+        return 0;
+}
+
 int unit_name_printf(const Unit *u, const char* format, char **ret) {
         /*
          * This will use the passed string as format string and replace the following specifiers (which should all be
@@ -191,6 +205,7 @@ int unit_full_printf_full(const Unit *u, const char *format, size_t max_length,
          * %R: the root of this systemd's instance tree (deprecated)
          *
          * %C: the cache directory root (e.g. /var/cache or $XDG_CACHE_HOME)
+         * %d: the credentials directory ($CREDENTIALS_DIRECTORY)
          * %E: the configuration directory root (e.g. /etc or $XDG_CONFIG_HOME)
          * %L: the log directory root (e.g. /var/log or $XDG_CONFIG_HOME/log)
          * %S: the state directory root (e.g. /var/lib or $XDG_CONFIG_HOME)
@@ -227,6 +242,7 @@ int unit_full_printf_full(const Unit *u, const char *format, size_t max_length,
                 { 'R', specifier_cgroup_root,              NULL },
 
                 { 'C', specifier_special_directory,        UINT_TO_PTR(EXEC_DIRECTORY_CACHE) },
+                { 'd', specifier_credentials_dir,          NULL },
                 { 'E', specifier_special_directory,        UINT_TO_PTR(EXEC_DIRECTORY_CONFIGURATION) },
                 { 'L', specifier_special_directory,        UINT_TO_PTR(EXEC_DIRECTORY_LOGS) },
                 { 'S', specifier_special_directory,        UINT_TO_PTR(EXEC_DIRECTORY_STATE) },

src/test/test-execute.c

@@ -1086,6 +1086,7 @@ static void test_exec_specifier(Manager *m) {
         test(m, "exec-specifier.service", 0, CLD_EXITED);
         test(m, "exec-specifier@foo-bar.service", 0, CLD_EXITED);
         test(m, "exec-specifier-interpolation.service", 0, CLD_EXITED);
+        test(m, "exec-specifier-credentials-dir.service", 0, CLD_EXITED);
 }
 
 static void test_exec_standardinput(Manager *m) {

test/test-execute/exec-specifier-credentials-dir.service

@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[Unit]
+Description=Test for specifiers
+
+[Service]
+Type=oneshot
+Environment=TOP_SECRET=%d/very_top_secret
+# Test if the specifier is resolved correctly both before and after LoadCredential=
+ExecStart=test %d/very_top_secret = "${CREDENTIALS_DIRECTORY}/very_top_secret"
+LoadCredential=very_top_secret
+ExecStart=test %d/very_top_secret = "${CREDENTIALS_DIRECTORY}/very_top_secret"
+ExecStart=sh -c 'test %d/very_top_secret = "$TOP_SECRET"'

test/test-execute/exec-specifier.service

@@ -20,6 +20,7 @@ ExecStart=test %L = /var/log
 ExecStart=test %E = /etc
 ExecStart=test %T = /tmp
 ExecStart=test %V = /var/tmp
+ExecStart=test %d = %t/credentials/%n
 ExecStart=sh -c 'test %u = $$(id -un)'
 ExecStart=sh -c 'test %U = $$(id -u)'
 ExecStart=sh -c 'test %g = $$(id -gn)'