path: root/src/shared/exec-util.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <dirent.h>
#include <errno.h>
#include <sys/prctl.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>

#include "alloc-util.h"
#include "conf-files.h"
#include "env-file.h"
#include "env-util.h"
#include "errno-util.h"
#include "exec-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "hashmap.h"
#include "macro.h"
#include "missing_syscall.h"
#include "process-util.h"
#include "rlimit-util.h"
#include "serialize.h"
#include "set.h"
#include "signal-util.h"
#include "stat-util.h"
#include "string-table.h"
#include "string-util.h"
#include "strv.h"
#include "terminal-util.h"
#include "tmpfile-util.h"

/* Put this test here for a lack of better place */
assert_cc(EAGAIN == EWOULDBLOCK);

static int do_spawn(const char *path, char *argv[], int stdout_fd, pid_t *pid, bool set_systemd_exec_pid) {
        pid_t _pid;
        int r;

        if (null_or_empty_path(path)) {
                log_debug("%s is empty (a mask).", path);
                return 0;
        }

        r = safe_fork("(direxec)", FORK_DEATHSIG|FORK_LOG, &_pid);
        if (r < 0)
                return r;
        if (r == 0) {
                char *_argv[2];

                if (stdout_fd >= 0) {
                        r = rearrange_stdio(STDIN_FILENO, TAKE_FD(stdout_fd), STDERR_FILENO);
                        if (r < 0)
                                _exit(EXIT_FAILURE);
                }

                (void) rlimit_nofile_safe();

                if (set_systemd_exec_pid) {
                        r = setenv_systemd_exec_pid(false);
                        if (r < 0)
                                log_warning_errno(r, "Failed to set $SYSTEMD_EXEC_PID, ignoring: %m");
                }

                if (!argv) {
                        _argv[0] = (char*) path;
                        _argv[1] = NULL;
                        argv = _argv;
                } else
                        argv[0] = (char*) path;

                execv(path, argv);
                log_error_errno(errno, "Failed to execute %s: %m", path);
                _exit(EXIT_FAILURE);
        }

        *pid = _pid;
        return 1;
}

static int do_execute(
                char **directories,
                usec_t timeout,
                gather_stdout_callback_t const callbacks[_STDOUT_CONSUME_MAX],
                void* const callback_args[_STDOUT_CONSUME_MAX],
                int output_fd,
                char *argv[],
                char *envp[],
                ExecDirFlags flags) {

        _cleanup_hashmap_free_free_ Hashmap *pids = NULL;
        _cleanup_strv_free_ char **paths = NULL;
        int r;
        bool parallel_execution;

        /* We fork this all off from a child process so that we can somewhat cleanly make
         * use of SIGALRM to set a time limit.
         *
         * We attempt to perform parallel execution if configured by the user, however
         * if `callbacks` is nonnull, execution must be serial.
         */
        parallel_execution = FLAGS_SET(flags, EXEC_DIR_PARALLEL) && !callbacks;

        r = conf_files_list_strv(&paths, NULL, NULL, CONF_FILES_EXECUTABLE|CONF_FILES_REGULAR|CONF_FILES_FILTER_MASKED, (const char* const*) directories);
        if (r < 0)
                return log_error_errno(r, "Failed to enumerate executables: %m");

        if (parallel_execution) {
                pids = hashmap_new(NULL);
                if (!pids)
                        return log_oom();
        }

        /* Abort execution of this process after the timeout. We simply rely on SIGALRM as
         * default action terminating the process, and turn on alarm(). */

        if (timeout != USEC_INFINITY)
                alarm(DIV_ROUND_UP(timeout, USEC_PER_SEC));

        STRV_FOREACH(e, envp)
                if (putenv(*e) != 0)
                        return log_error_errno(errno, "Failed to set environment variable: %m");

        STRV_FOREACH(path, paths) {
                _cleanup_free_ char *t = NULL;
                _cleanup_close_ int fd = -EBADF;
                pid_t pid;

                t = strdup(*path);
                if (!t)
                        return log_oom();

                if (callbacks) {
                        fd = open_serialization_fd(basename(*path));
                        if (fd < 0)
                                return log_error_errno(fd, "Failed to open serialization file: %m");
                }

                r = do_spawn(t, argv, fd, &pid, FLAGS_SET(flags, EXEC_DIR_SET_SYSTEMD_EXEC_PID));
                if (r <= 0)
                        continue;

                if (parallel_execution) {
                        r = hashmap_put(pids, PID_TO_PTR(pid), t);
                        if (r < 0)
                                return log_oom();
                        t = NULL;
                } else {
                        r = wait_for_terminate_and_check(t, pid, WAIT_LOG);
                        if (FLAGS_SET(flags, EXEC_DIR_IGNORE_ERRORS)) {
                                if (r < 0)
                                        continue;
                        } else if (r > 0)
                                return r;

                        if (callbacks) {
                                if (lseek(fd, 0, SEEK_SET) < 0)
                                        return log_error_errno(errno, "Failed to seek on serialization fd: %m");

                                r = callbacks[STDOUT_GENERATE](fd, callback_args[STDOUT_GENERATE]);
                                fd = -EBADF;
                                if (r < 0)
                                        return log_error_errno(r, "Failed to process output from %s: %m", *path);
                        }
                }
        }

        if (callbacks) {
                r = callbacks[STDOUT_COLLECT](output_fd, callback_args[STDOUT_COLLECT]);
                if (r < 0)
                        return log_error_errno(r, "Callback two failed: %m");
        }

        while (!hashmap_isempty(pids)) {
                _cleanup_free_ char *t = NULL;
                pid_t pid;

                pid = PTR_TO_PID(hashmap_first_key(pids));
                assert(pid > 0);

                t = hashmap_remove(pids, PID_TO_PTR(pid));
                assert(t);

                r = wait_for_terminate_and_check(t, pid, WAIT_LOG);
                if (!FLAGS_SET(flags, EXEC_DIR_IGNORE_ERRORS) && r > 0)
                        return r;
        }

        return 0;
}

int execute_directories(
                const char* const* directories,
                usec_t timeout,
                gather_stdout_callback_t const callbacks[_STDOUT_CONSUME_MAX],
                void* const callback_args[_STDOUT_CONSUME_MAX],
                char *argv[],
                char *envp[],
                ExecDirFlags flags) {

        char **dirs = (char**) directories;
        _cleanup_close_ int fd = -EBADF;
        char *name;
        int r;
        pid_t executor_pid;

        assert(!strv_isempty(dirs));

        name = basename(dirs[0]);
        assert(!isempty(name));

        if (callbacks) {
                assert(callback_args);
                assert(callbacks[STDOUT_GENERATE]);
                assert(callbacks[STDOUT_COLLECT]);
                assert(callbacks[STDOUT_CONSUME]);

                fd = open_serialization_fd(name);
                if (fd < 0)
                        return log_error_errno(fd, "Failed to open serialization file: %m");
        }

        /* Executes all binaries in the directories serially or in parallel and waits for
         * them to finish. Optionally a timeout is applied. If a file with the same name
         * exists in more than one directory, the earliest one wins. */

        r = safe_fork("(sd-executor)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_LOG, &executor_pid);
        if (r < 0)
                return r;
        if (r == 0) {
                r = do_execute(dirs, timeout, callbacks, callback_args, fd, argv, envp, flags);
                _exit(r < 0 ? EXIT_FAILURE : r);
        }

        r = wait_for_terminate_and_check("(sd-executor)", executor_pid, 0);
        if (r < 0)
                return r;
        if (!FLAGS_SET(flags, EXEC_DIR_IGNORE_ERRORS) && r > 0)
                return r;

        if (!callbacks)
                return 0;

        if (lseek(fd, 0, SEEK_SET) < 0)
                return log_error_errno(errno, "Failed to rewind serialization fd: %m");

        r = callbacks[STDOUT_CONSUME](fd, callback_args[STDOUT_CONSUME]);
        fd = -EBADF;
        if (r < 0)
                return log_error_errno(r, "Failed to parse returned data: %m");
        return 0;
}

static int gather_environment_generate(int fd, void *arg) {
        char ***env = ASSERT_PTR(arg);
        _cleanup_fclose_ FILE *f = NULL;
        _cleanup_strv_free_ char **new = NULL;
        int r;

        /* Read a series of VAR=value assignments from fd, use them to update the list of
         * variables in env. Also update the exported environment.
         *
         * fd is always consumed, even on error.
         */

        f = fdopen(fd, "r");
        if (!f) {
                safe_close(fd);
                return -errno;
        }

        r = load_env_file_pairs(f, NULL, &new);
        if (r < 0)
                return r;

        STRV_FOREACH_PAIR(x, y, new) {
                if (!env_name_is_valid(*x)) {
                        log_warning("Invalid variable assignment \"%s=...\", ignoring.", *x);
                        continue;
                }

                r = strv_env_assign(env, *x, *y);
                if (r < 0)
                        return r;

                if (setenv(*x, *y, true) < 0)
                        return -errno;
        }

        return 0;
}

static int gather_environment_collect(int fd, void *arg) {
        _cleanup_fclose_ FILE *f = NULL;
        char ***env = ASSERT_PTR(arg);
        int r;

        /* Write out a series of env=cescape(VAR=value) assignments to fd. */

        f = fdopen(fd, "w");
        if (!f) {
                safe_close(fd);
                return -errno;
        }

        r = serialize_strv(f, "env", *env);
        if (r < 0)
                return r;

        r = fflush_and_check(f);
        if (r < 0)
                return r;

        return 0;
}

static int gather_environment_consume(int fd, void *arg) {
        _cleanup_fclose_ FILE *f = NULL;
        char ***env = ASSERT_PTR(arg);
        int r = 0;

        /* Read a series of env=cescape(VAR=value) assignments from fd into env. */

        f = fdopen(fd, "r");
        if (!f) {
                safe_close(fd);
                return -errno;
        }

        for (;;) {
                _cleanup_free_ char *line = NULL;
                const char *v;
                int k;

                k = read_line(f, LONG_LINE_MAX, &line);
                if (k < 0)
                        return k;
                if (k == 0)
                        break;

                v = startswith(line, "env=");
                if (!v) {
                        log_debug("Serialization line \"%s\" unexpectedly didn't start with \"env=\".", line);
                        if (r == 0)
                                r = -EINVAL;

                        continue;
                }

                k = deserialize_environment(v, env);
                if (k < 0) {
                        log_debug_errno(k, "Invalid serialization line \"%s\": %m", line);

                        if (r == 0)
                                r = k;
                }
        }

        return r;
}

int exec_command_flags_from_strv(char **ex_opts, ExecCommandFlags *flags) {
        ExecCommandFlags ex_flag, ret_flags = 0;

        assert(flags);

        STRV_FOREACH(opt, ex_opts) {
                ex_flag = exec_command_flags_from_string(*opt);
                if (ex_flag < 0)
                        return ex_flag;
                ret_flags |= ex_flag;
        }

        *flags = ret_flags;

        return 0;
}

int exec_command_flags_to_strv(ExecCommandFlags flags, char ***ex_opts) {
        _cleanup_strv_free_ char **ret_opts = NULL;
        ExecCommandFlags it = flags;
        const char *str;
        int i, r;

        assert(ex_opts);

        if (flags < 0)
                return flags;

        for (i = 0; it != 0; it &= ~(1 << i), i++) {
                if (FLAGS_SET(flags, (1 << i))) {
                        str = exec_command_flags_to_string(1 << i);
                        if (!str)
                                return -EINVAL;

                        r = strv_extend(&ret_opts, str);
                        if (r < 0)
                                return r;
                }
        }

        *ex_opts = TAKE_PTR(ret_opts);

        return 0;
}

const gather_stdout_callback_t gather_environment[] = {
        gather_environment_generate,
        gather_environment_collect,
        gather_environment_consume,
};

static const char* const exec_command_strings[] = {
        "ignore-failure", /* EXEC_COMMAND_IGNORE_FAILURE */
        "privileged",     /* EXEC_COMMAND_FULLY_PRIVILEGED */
        "no-setuid",      /* EXEC_COMMAND_NO_SETUID */
        "ambient",        /* EXEC_COMMAND_AMBIENT_MAGIC */
        "no-env-expand",  /* EXEC_COMMAND_NO_ENV_EXPAND */
};

const char* exec_command_flags_to_string(ExecCommandFlags i) {
        size_t idx;

        for (idx = 0; idx < ELEMENTSOF(exec_command_strings); idx++)
                if (i == (1 << idx))
                        return exec_command_strings[idx];

        return NULL;
}

ExecCommandFlags exec_command_flags_from_string(const char *s) {
        ssize_t idx;

        idx = string_table_lookup(exec_command_strings, ELEMENTSOF(exec_command_strings), s);

        if (idx < 0)
                return _EXEC_COMMAND_FLAGS_INVALID;
        else
                return 1 << idx;
}

int fexecve_or_execve(int executable_fd, const char *executable, char *const argv[], char *const envp[]) {
        /* Refuse invalid fds, regardless if fexecve() use is enabled or not */
        if (executable_fd < 0)
                return -EBADF;

        /* Block any attempts on exploiting Linux' liberal argv[] handling, i.e. CVE-2021-4034 and suchlike */
        if (isempty(executable) || strv_isempty(argv))
                return -EINVAL;

#if ENABLE_FEXECVE

        execveat(executable_fd, "", argv, envp, AT_EMPTY_PATH);

        if (IN_SET(errno, ENOSYS, ENOENT) || ERRNO_IS_PRIVILEGE(errno))
                /* Old kernel or a script or an overzealous seccomp filter? Let's fall back to execve().
                 *
                 * fexecve(3): "If fd refers to a script (i.e., it is an executable text file that names a
                 * script interpreter with a first line that begins with the characters #!) and the
                 * close-on-exec flag has been set for fd, then fexecve() fails with the error ENOENT. This
                 * error occurs because, by the time the script interpreter is executed, fd has already been
                 * closed because of the close-on-exec flag. Thus, the close-on-exec flag can't be set on fd
                 * if it refers to a script."
                 *
                 * Unfortunately, if we unset close-on-exec, the script will be executed just fine, but (at
                 * least in case of bash) the script name, $0, will be shown as /dev/fd/nnn, which breaks
                 * scripts which make use of $0. Thus, let's fall back to execve() in this case.
                 */
#endif
                execve(executable, argv, envp);
        return -errno;
}

int fork_agent(const char *name, const int except[], size_t n_except, pid_t *ret_pid, const char *path, ...) {
        bool stdout_is_tty, stderr_is_tty;
        size_t n, i;
        va_list ap;
        char **l;
        int r;

        assert(path);

        /* Spawns a temporary TTY agent, making sure it goes away when we go away */

        r = safe_fork_full(name,
                           except,
                           n_except,
                           FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_CLOSE_ALL_FDS|FORK_REOPEN_LOG,
                           ret_pid);
        if (r < 0)
                return r;
        if (r > 0)
                return 0;

        /* In the child: */

        stdout_is_tty = isatty(STDOUT_FILENO);
        stderr_is_tty = isatty(STDERR_FILENO);

        if (!stdout_is_tty || !stderr_is_tty) {
                int fd;

                /* Detach from stdout/stderr and reopen /dev/tty for them. This is important to ensure that
                 * when systemctl is started via popen() or a similar call that expects to read EOF we
                 * actually do generate EOF and not delay this indefinitely by keeping an unused copy of
                 * stdin around. */
                fd = open("/dev/tty", O_WRONLY);
                if (fd < 0) {
                        if (errno != ENXIO) {
                                log_error_errno(errno, "Failed to open /dev/tty: %m");
                                _exit(EXIT_FAILURE);
                        }

                        /* If we get ENXIO here we have no controlling TTY even though stdout/stderr are
                         * connected to a TTY. That's a weird setup, but let's handle it gracefully: let's
                         * skip the forking of the agents, given the TTY setup is not in order. */
                } else {
                        if (!stdout_is_tty && dup2(fd, STDOUT_FILENO) < 0) {
                                log_error_errno(errno, "Failed to dup2 /dev/tty: %m");
                                _exit(EXIT_FAILURE);
                        }

                        if (!stderr_is_tty && dup2(fd, STDERR_FILENO) < 0) {
                                log_error_errno(errno, "Failed to dup2 /dev/tty: %m");
                                _exit(EXIT_FAILURE);
                        }

                        fd = safe_close_above_stdio(fd);
                }
        }

        (void) rlimit_nofile_safe();

        /* Count arguments */
        va_start(ap, path);
        for (n = 0; va_arg(ap, char*); n++)
                ;
        va_end(ap);

        /* Allocate strv */
        l = newa(char*, n + 1);

        /* Fill in arguments */
        va_start(ap, path);
        for (i = 0; i <= n; i++)
                l[i] = va_arg(ap, char*);
        va_end(ap);

        execv(path, l);
        _exit(EXIT_FAILURE);
}