execute: Add new PassEnvironment= directive

This directive allows passing environment variables from the system
manager to spawned services. Variables in the system manager can be set
inside a container by passing `--set-env=...` options to systemd-spawn.

Tested with an on-disk test.service unit. Tested using multiple variable
names on a single line, with an empty setting to clear the current list
of variables, with non-existing variables.

Tested using `systemd-run -p PassEnvironment=VARNAME` to confirm it
works with transient units.

Confirmed that `systemctl show` will display the PassEnvironment
settings.

Checked that man pages are generated correctly.

No regressions in `make check`.

6 files changed, 141 insertions, 2 deletions

diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
index db4206a523..093179c003 100644
--- a/src/core/dbus-execute.c
+++ b/src/core/dbus-execute.c
@@ -629,6 +629,7 @@ const sd_bus_vtable bus_exec_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_PROPERTY("Environment", "as", NULL, offsetof(ExecContext, environment), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("EnvironmentFiles", "a(sb)", property_get_environment_files, 0, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("PassEnvironment", "as", NULL, offsetof(ExecContext, pass_environment), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("UMask", "u", bus_property_get_mode, offsetof(ExecContext, umask), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("LimitCPU", "t", bus_property_get_rlimit, offsetof(ExecContext, rlimit[RLIMIT_CPU]), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("LimitFSIZE", "t", bus_property_get_rlimit, offsetof(ExecContext, rlimit[RLIMIT_FSIZE]), SD_BUS_VTABLE_PROPERTY_CONST),
@@ -1289,6 +1290,38 @@ int bus_exec_context_set_transient_property(
 
                 return 1;
 
+        } else if (streq(name, "PassEnvironment")) {
+
+                _cleanup_strv_free_ char **l = NULL;
+
+                r = sd_bus_message_read_strv(message, &l);
+                if (r < 0)
+                        return r;
+
+                if (!strv_env_name_is_valid(l))
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid PassEnvironment block.");
+
+                if (mode != UNIT_CHECK) {
+                        if (strv_isempty(l)) {
+                                c->pass_environment = strv_free(c->pass_environment);
+                                unit_write_drop_in_private_format(u, mode, name, "PassEnvironment=\n");
+                        } else {
+                                _cleanup_free_ char *joined = NULL;
+
+                                r = strv_extend_strv(&c->pass_environment, l, true);
+                                if (r < 0)
+                                        return r;
+
+                                joined = strv_join_quoted(c->pass_environment);
+                                if (!joined)
+                                        return -ENOMEM;
+
+                                unit_write_drop_in_private_format(u, mode, name, "PassEnvironment=%s\n", joined);
+                        }
+                }
+
+                return 1;
+
         } else if (STR_IN_SET(name, "ReadWriteDirectories", "ReadOnlyDirectories", "InaccessibleDirectories")) {
 
                 _cleanup_strv_free_ char **l = NULL;
diff --git a/src/core/execute.c b/src/core/execute.c
index d751065af0..07979bf8b3 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -1332,6 +1332,34 @@ static int build_environment(
         return 0;
 }
 
+static int build_pass_environment(const ExecContext *c, char ***ret) {
+        _cleanup_strv_free_ char **pass_env = NULL;
+        size_t n_env = 0, n_bufsize = 0;
+        char **i;
+
+        STRV_FOREACH(i, c->pass_environment) {
+                _cleanup_free_ char *x = NULL;
+                char *v;
+
+                v = getenv(*i);
+                if (!v)
+                        continue;
+                x = strjoin(*i, "=", v, NULL);
+                if (!x)
+                        return -ENOMEM;
+                if (!GREEDY_REALLOC(pass_env, n_bufsize, n_env + 2))
+                        return -ENOMEM;
+                pass_env[n_env++] = x;
+                pass_env[n_env] = NULL;
+                x = NULL;
+        }
+
+        *ret = pass_env;
+        pass_env = NULL;
+
+        return 0;
+}
+
 static bool exec_needs_mount_namespace(
                 const ExecContext *context,
                 const ExecParameters *params,
@@ -1412,7 +1440,7 @@ static int exec_child(
                 char **files_env,
                 int *exit_status) {
 
-        _cleanup_strv_free_ char **our_env = NULL, **pam_env = NULL, **final_env = NULL, **final_argv = NULL;
+        _cleanup_strv_free_ char **our_env = NULL, **pass_env = NULL, **pam_env = NULL, **final_env = NULL, **final_argv = NULL;
         _cleanup_free_ char *mac_selinux_context_net = NULL;
         const char *username = NULL, *home = NULL, *shell = NULL, *wd;
         uid_t uid = UID_INVALID;
@@ -1928,9 +1956,16 @@ static int exec_child(
                 return r;
         }
 
-        final_env = strv_env_merge(5,
+        r = build_pass_environment(context, &pass_env);
+        if (r < 0) {
+                *exit_status = EXIT_MEMORY;
+                return r;
+        }
+
+        final_env = strv_env_merge(6,
                                    params->environment,
                                    our_env,
+                                   pass_env,
                                    context->environment,
                                    files_env,
                                    pam_env,
@@ -2088,6 +2123,7 @@ void exec_context_done(ExecContext *c) {
 
         c->environment = strv_free(c->environment);
         c->environment_files = strv_free(c->environment_files);
+        c->pass_environment = strv_free(c->pass_environment);
 
         for (l = 0; l < ELEMENTSOF(c->rlimit); l++)
                 c->rlimit[l] = mfree(c->rlimit[l]);
@@ -2358,6 +2394,9 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
         STRV_FOREACH(e, c->environment_files)
                 fprintf(f, "%sEnvironmentFile: %s\n", prefix, *e);
 
+        STRV_FOREACH(e, c->pass_environment)
+                fprintf(f, "%sPassEnvironment: %s\n", prefix, *e);
+
         fprintf(f, "%sRuntimeDirectoryMode: %04o\n", prefix, c->runtime_directory_mode);
 
         STRV_FOREACH(d, c->runtime_directory)
diff --git a/src/core/execute.h b/src/core/execute.h
index f8995a4203..1faff160cb 100644
--- a/src/core/execute.h
+++ b/src/core/execute.h
@@ -99,6 +99,7 @@ struct ExecRuntime {
 struct ExecContext {
         char **environment;
         char **environment_files;
+        char **pass_environment;
 
         struct rlimit *rlimit[_RLIMIT_MAX];
         char *working_directory, *root_directory;
diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4
index 75b11ee4f2..3294054ef7 100644
--- a/src/core/load-fragment-gperf.gperf.m4
+++ b/src/core/load-fragment-gperf.gperf.m4
@@ -33,6 +33,7 @@ $1.CPUAffinity,                  config_parse_exec_cpu_affinity,     0,
 $1.UMask,                        config_parse_mode,                  0,                             offsetof($1, exec_context.umask)
 $1.Environment,                  config_parse_environ,               0,                             offsetof($1, exec_context.environment)
 $1.EnvironmentFile,              config_parse_unit_env_file,         0,                             offsetof($1, exec_context.environment_files)
+$1.PassEnvironment,              config_parse_pass_environ,          0,                             offsetof($1, exec_context.pass_environment)
 $1.StandardInput,                config_parse_input,                 0,                             offsetof($1, exec_context.std_input)
 $1.StandardOutput,               config_parse_output,                0,                             offsetof($1, exec_context.std_output)
 $1.StandardError,                config_parse_output,                0,                             offsetof($1, exec_context.std_error)
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index 79cabd26e7..53d96dee14 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -2196,6 +2196,70 @@ int config_parse_environ(const char *unit,
         return 0;
 }
 
+int config_parse_pass_environ(const char *unit,
+                              const char *filename,
+                              unsigned line,
+                              const char *section,
+                              unsigned section_line,
+                              const char *lvalue,
+                              int ltype,
+                              const char *rvalue,
+                              void *data,
+                              void *userdata) {
+
+        const char *whole_rvalue = rvalue;
+        char*** passenv = data;
+        _cleanup_strv_free_ char **n = NULL;
+        size_t nlen = 0, nbufsize = 0;
+        int r;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+        assert(data);
+
+        if (isempty(rvalue)) {
+                /* Empty assignment resets the list */
+                *passenv = strv_free(*passenv);
+                return 0;
+        }
+
+        for (;;) {
+                _cleanup_free_ char *word = NULL;
+
+                r = extract_first_word(&rvalue, &word, WHITESPACE, EXTRACT_QUOTES);
+                if (r == 0)
+                        break;
+                if (r == -ENOMEM)
+                        return log_oom();
+                if (r < 0) {
+                        log_syntax(unit, LOG_ERR, filename, line, r,
+                                   "Trailing garbage in %s, ignoring: %s", lvalue, whole_rvalue);
+                        break;
+                }
+
+                if (!env_name_is_valid(word)) {
+                        log_syntax(unit, LOG_ERR, filename, line, EINVAL,
+                                   "Invalid environment name for %s, ignoring: %s", lvalue, word);
+                        continue;
+                }
+
+                if (!GREEDY_REALLOC(n, nbufsize, nlen + 2))
+                        return log_oom();
+                n[nlen++] = word;
+                n[nlen] = NULL;
+                word = NULL;
+        }
+
+        if (n) {
+                r = strv_extend_strv(passenv, n, true);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
 int config_parse_ip_tos(const char *unit,
                         const char *filename,
                         unsigned line,
diff --git a/src/core/load-fragment.h b/src/core/load-fragment.h
index 0cf821289c..eb4de1582f 100644
--- a/src/core/load-fragment.h
+++ b/src/core/load-fragment.h
@@ -84,6 +84,7 @@ int config_parse_syscall_filter(const char *unit, const char *filename, unsigned
 int config_parse_syscall_archs(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_syscall_errno(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_environ(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
+int config_parse_pass_environ(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_unit_slice(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_cpu_shares(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_memory_limit(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);