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core: accept "|" ExecStart= prefix to spawn target user's shell

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When switching to another user it's oftentimes desirable to also spawn
the target user's shell. sudo supports this via -i flag, run0 currently
doesn't. We don't want to proactively query NSS ourselves, since
that would fall short when operating remotely. Let's instead teach
the service manager to spawn the command using the user's default shell.

I opted for "|" instead of "." in the end because the latter seems
a bit obscure. But happy to change it to something else if a better option
comes up.
This commit is contained in:
Mike Yuan
2025-05-07 18:32:19 +02:00
parent 398b3e4472
commit 5b8bcbcf00
8 changed files with 192 additions and 87 deletions
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src/core/exec-invoke.c
+48 -12
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@@ -4572,12 +4572,11 @@ int exec_invoke(
const CGroupContext *cgroup_context,
int *exit_status) {
_cleanup_strv_free_ char **our_env = NULL, **pass_env = NULL, **joined_exec_search_path = NULL, **accum_env = NULL, **replaced_argv = NULL;
_cleanup_strv_free_ char **our_env = NULL, **pass_env = NULL, **joined_exec_search_path = NULL, **accum_env = NULL;
int r;
const char *username = NULL, *groupname = NULL;
_cleanup_free_ char *home_buffer = NULL, *memory_pressure_path = NULL, *own_user = NULL;
const char *pwent_home = NULL, *shell = NULL;
char **final_argv = NULL;
dev_t journal_stream_dev = 0;
ino_t journal_stream_ino = 0;
bool needs_sandboxing, /* Do we need to set up full sandboxing? (i.e. all namespacing, all MAC stuff, caps, yadda yadda */
@@ -4807,7 +4806,7 @@ int exec_invoke(
if (context->user)
u = context->user;
else if (context->pam_name) {
else if (context->pam_name || FLAGS_SET(command->flags, EXEC_COMMAND_VIA_SHELL)) {
/* If PAM is enabled but no user name is explicitly selected, then use our own one. */
own_user = getusername_malloc();
if (!own_user) {
@@ -5406,17 +5405,26 @@ int exec_invoke(
/* Now that the mount namespace has been set up and privileges adjusted, let's look for the thing we
* shall execute. */
const char *path = command->path;
if (FLAGS_SET(command->flags, EXEC_COMMAND_VIA_SHELL)) {
if (shell_is_placeholder(shell)) {
log_debug("Shell prefixing requested for user without default shell, using /bin/sh: %s",
strna(username));
assert(streq(path, _PATH_BSHELL));
} else
path = shell;
}
_cleanup_free_ char *executable = NULL;
_cleanup_close_ int executable_fd = -EBADF;
r = find_executable_full(command->path, /* root= */ NULL, context->exec_search_path, false, &executable, &executable_fd);
r = find_executable_full(path, /* root= */ NULL, context->exec_search_path, false, &executable, &executable_fd);
if (r < 0) {
*exit_status = EXIT_EXEC;
log_struct_errno(LOG_NOTICE, r,
LOG_MESSAGE_ID(SD_MESSAGE_SPAWN_FAILED_STR),
LOG_EXEC_MESSAGE(params,
"Unable to locate executable '%s': %m",
command->path),
LOG_ITEM("EXECUTABLE=%s", command->path));
LOG_EXEC_MESSAGE(params, "Unable to locate executable '%s': %m", path),
LOG_ITEM("EXECUTABLE=%s", path));
/* If the error will be ignored by manager, tune down the log level here. Missing executable
* is very much expected in this case. */
return r != -ENOMEM && FLAGS_SET(command->flags, EXEC_COMMAND_IGNORE_FAILURE) ? 1 : r;
@@ -5827,10 +5835,13 @@ int exec_invoke(
strv_free_and_replace(accum_env, ee);
}
if (!FLAGS_SET(command->flags, EXEC_COMMAND_NO_ENV_EXPAND)) {
_cleanup_strv_free_ char **replaced_argv = NULL, **argv_via_shell = NULL;
char **final_argv = FLAGS_SET(command->flags, EXEC_COMMAND_VIA_SHELL) ? strv_skip(command->argv, 1) : command->argv;
if (final_argv && !FLAGS_SET(command->flags, EXEC_COMMAND_NO_ENV_EXPAND)) {
_cleanup_strv_free_ char **unset_variables = NULL, **bad_variables = NULL;
r = replace_env_argv(command->argv, accum_env, &replaced_argv, &unset_variables, &bad_variables);
r = replace_env_argv(final_argv, accum_env, &replaced_argv, &unset_variables, &bad_variables);
if (r < 0) {
*exit_status = EXIT_MEMORY;
return log_error_errno(r, "Failed to replace environment variables: %m");
@@ -5846,8 +5857,33 @@ int exec_invoke(
_cleanup_free_ char *jb = strv_join(bad_variables, ", ");
log_warning("Invalid environment variable name evaluates to an empty string: %s", strna(jb));
}
} else
final_argv = command->argv;
}
if (FLAGS_SET(command->flags, EXEC_COMMAND_VIA_SHELL)) {
r = strv_extendf(&argv_via_shell, "%s%s", command->argv[0][0] == '-' ? "-" : "", path);
if (r < 0) {
*exit_status = EXIT_MEMORY;
return log_oom();
}
if (!strv_isempty(final_argv)) {
_cleanup_free_ char *cmdline_joined = NULL;
cmdline_joined = strv_join(final_argv, " ");
if (!cmdline_joined) {
*exit_status = EXIT_MEMORY;
return log_oom();
}
r = strv_extend_many(&argv_via_shell, "-c", cmdline_joined);
if (r < 0) {
*exit_status = EXIT_MEMORY;
return log_oom();
}
}
final_argv = argv_via_shell;
}
log_command_line(context, params, "Executing", executable, final_argv);