diff options
Diffstat (limited to 'src/shared/pager.c')
| -rw-r--r-- | src/shared/pager.c | 330 |
1 files changed, 330 insertions, 0 deletions
diff --git a/src/shared/pager.c b/src/shared/pager.c new file mode 100644 index 0000000..19deefa --- /dev/null +++ b/src/shared/pager.c @@ -0,0 +1,330 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <errno.h> +#include <stddef.h> +#include <stdint.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/prctl.h> +#include <unistd.h> + +#include "sd-login.h" + +#include "copy.h" +#include "env-util.h" +#include "fd-util.h" +#include "fileio.h" +#include "io-util.h" +#include "locale-util.h" +#include "log.h" +#include "macro.h" +#include "pager.h" +#include "process-util.h" +#include "rlimit-util.h" +#include "signal-util.h" +#include "string-util.h" +#include "strv.h" +#include "terminal-util.h" + +static pid_t pager_pid = 0; + +static int stored_stdout = -1; +static int stored_stderr = -1; +static bool stdout_redirected = false; +static bool stderr_redirected = false; + +_noreturn_ static void pager_fallback(void) { + int r; + + r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, UINT64_MAX, 0); + if (r < 0) { + log_error_errno(r, "Internal pager failed: %m"); + _exit(EXIT_FAILURE); + } + + _exit(EXIT_SUCCESS); +} + +static int no_quit_on_interrupt(int exe_name_fd, const char *less_opts) { + _cleanup_fclose_ FILE *file = NULL; + _cleanup_free_ char *line = NULL; + int r; + + assert(exe_name_fd >= 0); + assert(less_opts); + + /* This takes ownership of exe_name_fd */ + file = fdopen(exe_name_fd, "r"); + if (!file) { + safe_close(exe_name_fd); + return log_error_errno(errno, "Failed to create FILE object: %m"); + } + + /* Find the last line */ + for (;;) { + _cleanup_free_ char *t = NULL; + + r = read_line(file, LONG_LINE_MAX, &t); + if (r < 0) + return log_error_errno(r, "Failed to read from socket: %m"); + if (r == 0) + break; + + free_and_replace(line, t); + } + + /* We only treat "less" specially. + * Return true whenever option K is *not* set. */ + r = streq_ptr(line, "less") && !strchr(less_opts, 'K'); + + log_debug("Pager executable is \"%s\", options \"%s\", quit_on_interrupt: %s", + strnull(line), less_opts, yes_no(!r)); + return r; +} + +void pager_open(PagerFlags flags) { + _cleanup_close_pair_ int fd[2] = EBADF_PAIR, exe_name_pipe[2] = EBADF_PAIR; + _cleanup_strv_free_ char **pager_args = NULL; + _cleanup_free_ char *l = NULL; + const char *pager, *less_opts; + int r; + + if (flags & PAGER_DISABLE) + return; + + if (pager_pid > 0) + return; + + if (terminal_is_dumb()) + return; + + if (!is_main_thread()) + return (void) log_error_errno(SYNTHETIC_ERRNO(EPERM), "Pager invoked from wrong thread."); + + pager = getenv("SYSTEMD_PAGER"); + if (!pager) + pager = getenv("PAGER"); + + if (pager) { + pager_args = strv_split(pager, WHITESPACE); + if (!pager_args) + return (void) log_oom(); + + /* If the pager is explicitly turned off, honour it */ + if (strv_isempty(pager_args) || strv_equal(pager_args, STRV_MAKE("cat"))) + return; + } + + /* Determine and cache number of columns/lines before we spawn the pager so that we get the value from the + * actual tty */ + (void) columns(); + (void) lines(); + + if (pipe2(fd, O_CLOEXEC) < 0) + return (void) log_error_errno(errno, "Failed to create pager pipe: %m"); + + /* This is a pipe to feed the name of the executed pager binary into the parent */ + if (pipe2(exe_name_pipe, O_CLOEXEC) < 0) + return (void) log_error_errno(errno, "Failed to create exe_name pipe: %m"); + + /* Initialize a good set of less options */ + less_opts = getenv("SYSTEMD_LESS"); + if (!less_opts) + less_opts = "FRSXMK"; + if (flags & PAGER_JUMP_TO_END) { + l = strjoin(less_opts, " +G"); + if (!l) + return (void) log_oom(); + less_opts = l; + } + + /* We set SIGINT as PR_DEATHSIG signal here, to match the "K" parameter we set in $LESS, which enables SIGINT behaviour. */ + r = safe_fork("(pager)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGINT|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pager_pid); + if (r < 0) + return; + if (r == 0) { + const char *less_charset; + + /* In the child start the pager */ + + if (dup2(fd[0], STDIN_FILENO) < 0) { + log_error_errno(errno, "Failed to duplicate file descriptor to STDIN: %m"); + _exit(EXIT_FAILURE); + } + + safe_close_pair(fd); + + if (setenv("LESS", less_opts, 1) < 0) { + log_error_errno(errno, "Failed to set environment variable LESS: %m"); + _exit(EXIT_FAILURE); + } + + /* Initialize a good charset for less. This is particularly important if we output UTF-8 + * characters. */ + less_charset = getenv("SYSTEMD_LESSCHARSET"); + if (!less_charset && is_locale_utf8()) + less_charset = "utf-8"; + if (less_charset && + setenv("LESSCHARSET", less_charset, 1) < 0) { + log_error_errno(errno, "Failed to set environment variable LESSCHARSET: %m"); + _exit(EXIT_FAILURE); + } + + /* People might invoke us from sudo, don't needlessly allow less to be a way to shell out + * privileged stuff. If the user set $SYSTEMD_PAGERSECURE, trust their configuration of the + * pager. If they didn't, use secure mode when under euid is changed. If $SYSTEMD_PAGERSECURE + * wasn't explicitly set, and we autodetect the need for secure mode, only use the pager we + * know to be good. */ + int use_secure_mode = getenv_bool_secure("SYSTEMD_PAGERSECURE"); + bool trust_pager = use_secure_mode >= 0; + if (use_secure_mode == -ENXIO) { + uid_t uid; + + r = sd_pid_get_owner_uid(0, &uid); + if (r < 0) + log_debug_errno(r, "sd_pid_get_owner_uid() failed, enabling pager secure mode: %m"); + + use_secure_mode = r < 0 || uid != geteuid(); + + } else if (use_secure_mode < 0) { + log_warning_errno(use_secure_mode, "Unable to parse $SYSTEMD_PAGERSECURE, assuming true: %m"); + use_secure_mode = true; + } + + /* We generally always set variables used by less, even if we end up using a different pager. + * They shouldn't hurt in any case, and ideally other pagers would look at them too. */ + r = set_unset_env("LESSSECURE", use_secure_mode ? "1" : NULL, true); + if (r < 0) { + log_error_errno(r, "Failed to adjust environment variable LESSSECURE: %m"); + _exit(EXIT_FAILURE); + } + + if (trust_pager && pager_args) { /* The pager config might be set globally, and we cannot + * know if the user adjusted it to be appropriate for the + * secure mode. Thus, start the pager specified through + * envvars only when $SYSTEMD_PAGERSECURE was explicitly set + * as well. */ + r = loop_write(exe_name_pipe[1], pager_args[0], strlen(pager_args[0]) + 1); + if (r < 0) { + log_error_errno(r, "Failed to write pager name to socket: %m"); + _exit(EXIT_FAILURE); + } + + execvp(pager_args[0], pager_args); + log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno, + "Failed to execute '%s', using fallback pagers: %m", pager_args[0]); + } + + /* Debian's alternatives command for pagers is called 'pager'. Note that we do not call + * sensible-pagers here, since that is just a shell script that implements a logic that is + * similar to this one anyway, but is Debian-specific. */ + static const char* pagers[] = { "pager", "less", "more", "(built-in)" }; + + for (unsigned i = 0; i < ELEMENTSOF(pagers); i++) { + /* Only less (and our trivial fallback) implement secure mode right now. */ + if (use_secure_mode && !STR_IN_SET(pagers[i], "less", "(built-in)")) + continue; + + r = loop_write(exe_name_pipe[1], pagers[i], strlen(pagers[i]) + 1); + if (r < 0) { + log_error_errno(r, "Failed to write pager name to socket: %m"); + _exit(EXIT_FAILURE); + } + + if (i < ELEMENTSOF(pagers) - 1) { + execlp(pagers[i], pagers[i], NULL); + log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno, + "Failed to execute '%s', will try '%s' next: %m", pagers[i], pagers[i+1]); + } else { + /* Close pipe to signal the parent to start sending data */ + safe_close_pair(exe_name_pipe); + pager_fallback(); + assert_not_reached(); + } + } + } + + /* Return in the parent */ + stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3); + if (dup2(fd[1], STDOUT_FILENO) < 0) { + stored_stdout = safe_close(stored_stdout); + return (void) log_error_errno(errno, "Failed to duplicate pager pipe: %m"); + } + stdout_redirected = true; + + stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3); + if (dup2(fd[1], STDERR_FILENO) < 0) { + stored_stderr = safe_close(stored_stderr); + return (void) log_error_errno(errno, "Failed to duplicate pager pipe: %m"); + } + stderr_redirected = true; + + exe_name_pipe[1] = safe_close(exe_name_pipe[1]); + + r = no_quit_on_interrupt(TAKE_FD(exe_name_pipe[0]), less_opts); + if (r > 0) + (void) ignore_signals(SIGINT); +} + +void pager_close(void) { + + if (pager_pid <= 0) + return; + + /* Inform pager that we are done */ + (void) fflush(stdout); + if (stdout_redirected) + if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0) + (void) close(STDOUT_FILENO); + stored_stdout = safe_close(stored_stdout); + (void) fflush(stderr); + if (stderr_redirected) + if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0) + (void) close(STDERR_FILENO); + stored_stderr = safe_close(stored_stderr); + stdout_redirected = stderr_redirected = false; + + (void) kill(pager_pid, SIGCONT); + (void) wait_for_terminate(TAKE_PID(pager_pid), NULL); + pager_pid = 0; +} + +bool pager_have(void) { + return pager_pid > 0; +} + +int show_man_page(const char *desc, bool null_stdio) { + const char *args[4] = { "man", NULL, NULL, NULL }; + char *e = NULL; + pid_t pid; + size_t k; + int r; + + k = strlen(desc); + + if (desc[k-1] == ')') + e = strrchr(desc, '('); + + if (e) { + char *page = NULL, *section = NULL; + + page = strndupa_safe(desc, e - desc); + section = strndupa_safe(e + 1, desc + k - e - 2); + + args[1] = section; + args[2] = page; + } else + args[1] = desc; + + r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGTERM|(null_stdio ? FORK_REARRANGE_STDIO : 0)|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid); + if (r < 0) + return r; + if (r == 0) { + /* Child */ + execvp(args[0], (char**) args); + log_error_errno(errno, "Failed to execute man: %m"); + _exit(EXIT_FAILURE); + } + + return wait_for_terminate_and_check(NULL, pid, 0); +} |