src/shared/pager.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <errno.h>
   4 #include <stddef.h>
   5 #include <stdint.h>
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <sys/prctl.h>
   9 #include <unistd.h>
  10
  11 #include "sd-login.h"
  12
  13 #include "copy.h"
  14 #include "env-util.h"
  15 #include "fd-util.h"
  16 #include "fileio.h"
  17 #include "io-util.h"
  18 #include "locale-util.h"
  19 #include "log.h"
  20 #include "macro.h"
  21 #include "pager.h"
  22 #include "process-util.h"
  23 #include "rlimit-util.h"
  24 #include "signal-util.h"
  25 #include "string-util.h"
  26 #include "strv.h"
  27 #include "terminal-util.h"
  28 #include "util.h"
  29
  30 static pid_t pager_pid = 0;
  31
  32 static int stored_stdout = -1;
  33 static int stored_stderr = -1;
  34 static bool stdout_redirected = false;
  35 static bool stderr_redirected = false;
  36
  37 _noreturn_ static void pager_fallback(void) {
  38         int r;
  39
  40         r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, UINT64_MAX, 0);
  41         if (r < 0) {
  42                 log_error_errno(r, "Internal pager failed: %m");
  43                 _exit(EXIT_FAILURE);
  44         }
  45
  46         _exit(EXIT_SUCCESS);
  47 }
  48
  49 static int no_quit_on_interrupt(int exe_name_fd, const char *less_opts) {
  50         _cleanup_fclose_ FILE *file = NULL;
  51         _cleanup_free_ char *line = NULL;
  52         int r;
  53
  54         assert(exe_name_fd >= 0);
  55         assert(less_opts);
  56
  57         /* This takes ownership of exe_name_fd */
  58         file = fdopen(exe_name_fd, "r");
  59         if (!file) {
  60                 safe_close(exe_name_fd);
  61                 return log_error_errno(errno, "Failed to create FILE object: %m");
  62         }
  63
  64         /* Find the last line */
  65         for (;;) {
  66                 _cleanup_free_ char *t = NULL;
  67
  68                 r = read_line(file, LONG_LINE_MAX, &t);
  69                 if (r < 0)
  70                         return log_error_errno(r, "Failed to read from socket: %m");
  71                 if (r == 0)
  72                         break;
  73
  74                 free_and_replace(line, t);
  75         }
  76
  77         /* We only treat "less" specially.
  78          * Return true whenever option K is *not* set. */
  79         r = streq_ptr(line, "less") && !strchr(less_opts, 'K');
  80
  81         log_debug("Pager executable is \"%s\", options \"%s\", quit_on_interrupt: %s",
  82                   strnull(line), less_opts, yes_no(!r));
  83         return r;
  84 }
  85
  86 void pager_open(PagerFlags flags) {
  87         _cleanup_close_pair_ int fd[2] = { -1, -1 }, exe_name_pipe[2] = { -1, -1 };
  88         _cleanup_strv_free_ char **pager_args = NULL;
  89         _cleanup_free_ char *l = NULL;
  90         const char *pager, *less_opts;
  91         int r;
  92
  93         if (flags & PAGER_DISABLE)
  94                 return;
  95
  96         if (pager_pid > 0)
  97                 return;
  98
  99         if (terminal_is_dumb())
 100                 return;
 101
 102         if (!is_main_thread())
 103                 return (void) log_error_errno(SYNTHETIC_ERRNO(EPERM), "Pager invoked from wrong thread.");
 104
 105         pager = getenv("SYSTEMD_PAGER");
 106         if (!pager)
 107                 pager = getenv("PAGER");
 108
 109         if (pager) {
 110                 pager_args = strv_split(pager, WHITESPACE);
 111                 if (!pager_args)
 112                         return (void) log_oom();
 113
 114                 /* If the pager is explicitly turned off, honour it */
 115                 if (strv_isempty(pager_args) || strv_equal(pager_args, STRV_MAKE("cat")))
 116                         return;
 117         }
 118
 119         /* Determine and cache number of columns/lines before we spawn the pager so that we get the value from the
 120          * actual tty */
 121         (void) columns();
 122         (void) lines();
 123
 124         if (pipe2(fd, O_CLOEXEC) < 0)
 125                 return (void) log_error_errno(errno, "Failed to create pager pipe: %m");
 126
 127         /* This is a pipe to feed the name of the executed pager binary into the parent */
 128         if (pipe2(exe_name_pipe, O_CLOEXEC) < 0)
 129                 return (void) log_error_errno(errno, "Failed to create exe_name pipe: %m");
 130
 131         /* Initialize a good set of less options */
 132         less_opts = getenv("SYSTEMD_LESS");
 133         if (!less_opts)
 134                 less_opts = "FRSXMK";
 135         if (flags & PAGER_JUMP_TO_END) {
 136                 l = strjoin(less_opts, " +G");
 137                 if (!l)
 138                         return (void) log_oom();
 139                 less_opts = l;
 140         }
 141
 142         /* We set SIGINT as PR_DEATHSIG signal here, to match the "K" parameter we set in $LESS, which enables SIGINT behaviour. */
 143         r = safe_fork("(pager)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGINT|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pager_pid);
 144         if (r < 0)
 145                 return;
 146         if (r == 0) {
 147                 const char *less_charset, *exe;
 148
 149                 /* In the child start the pager */
 150
 151                 if (dup2(fd[0], STDIN_FILENO) < 0) {
 152                         log_error_errno(errno, "Failed to duplicate file descriptor to STDIN: %m");
 153                         _exit(EXIT_FAILURE);
 154                 }
 155
 156                 safe_close_pair(fd);
 157
 158                 if (setenv("LESS", less_opts, 1) < 0) {
 159                         log_error_errno(errno, "Failed to set environment variable LESS: %m");
 160                         _exit(EXIT_FAILURE);
 161                 }
 162
 163                 /* Initialize a good charset for less. This is particularly important if we output UTF-8
 164                  * characters. */
 165                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 166                 if (!less_charset && is_locale_utf8())
 167                         less_charset = "utf-8";
 168                 if (less_charset &&
 169                     setenv("LESSCHARSET", less_charset, 1) < 0) {
 170                         log_error_errno(errno, "Failed to set environment variable LESSCHARSET: %m");
 171                         _exit(EXIT_FAILURE);
 172                 }
 173
 174                 /* People might invoke us from sudo, don't needlessly allow less to be a way to shell out
 175                  * privileged stuff. If the user set $SYSTEMD_PAGERSECURE, trust their configuration of the
 176                  * pager. If they didn't, use secure mode when under euid is changed. If $SYSTEMD_PAGERSECURE
 177                  * wasn't explicitly set, and we autodetect the need for secure mode, only use the pager we
 178                  * know to be good. */
 179                 int use_secure_mode = getenv_bool_secure("SYSTEMD_PAGERSECURE");
 180                 bool trust_pager = use_secure_mode >= 0;
 181                 if (use_secure_mode == -ENXIO) {
 182                         uid_t uid;
 183
 184                         r = sd_pid_get_owner_uid(0, &uid);
 185                         if (r < 0)
 186                                 log_debug_errno(r, "sd_pid_get_owner_uid() failed, enabling pager secure mode: %m");
 187
 188                         use_secure_mode = r < 0 || uid != geteuid();
 189
 190                 } else if (use_secure_mode < 0) {
 191                         log_warning_errno(use_secure_mode, "Unable to parse $SYSTEMD_PAGERSECURE, assuming true: %m");
 192                         use_secure_mode = true;
 193                 }
 194
 195                 /* We generally always set variables used by less, even if we end up using a different pager.
 196                  * They shouldn't hurt in any case, and ideally other pagers would look at them too. */
 197                 r = set_unset_env("LESSSECURE", use_secure_mode ? "1" : NULL, true);
 198                 if (r < 0) {
 199                         log_error_errno(r, "Failed to adjust environment variable LESSSECURE: %m");
 200                         _exit(EXIT_FAILURE);
 201                 }
 202
 203                 if (trust_pager && pager_args) { /* The pager config might be set globally, and we cannot
 204                                                   * know if the user adjusted it to be appropriate for the
 205                                                   * secure mode. Thus, start the pager specified through
 206                                                   * envvars only when $SYSTEMD_PAGERSECURE was explicitly set
 207                                                   * as well. */
 208                         r = loop_write(exe_name_pipe[1], pager_args[0], strlen(pager_args[0]) + 1, false);
 209                         if (r < 0) {
 210                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 211                                 _exit(EXIT_FAILURE);
 212                         }
 213
 214                         execvp(pager_args[0], pager_args);
 215                         log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 216                                        "Failed to execute '%s', using fallback pagers: %m", pager_args[0]);
 217                 }
 218
 219                 /* Debian's alternatives command for pagers is called 'pager'. Note that we do not call
 220                  * sensible-pagers here, since that is just a shell script that implements a logic that is
 221                  * similar to this one anyway, but is Debian-specific. */
 222                 FOREACH_STRING(exe, "pager", "less", "more") {
 223                         /* Only less implements secure mode right now. */
 224                         if (use_secure_mode && !streq(exe, "less"))
 225                                 continue;
 226
 227                         r = loop_write(exe_name_pipe[1], exe, strlen(exe) + 1, false);
 228                         if (r  < 0) {
 229                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 230                                 _exit(EXIT_FAILURE);
 231                         }
 232                         execlp(exe, exe, NULL);
 233                         log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 234                                        "Failed to execute '%s', using next fallback pager: %m", exe);
 235                 }
 236
 237                 /* Our builtin is also very secure. */
 238                 r = loop_write(exe_name_pipe[1], "(built-in)", strlen("(built-in)") + 1, false);
 239                 if (r < 0) {
 240                         log_error_errno(r, "Failed to write pager name to socket: %m");
 241                         _exit(EXIT_FAILURE);
 242                 }
 243                 /* Close pipe to signal the parent to start sending data */
 244                 safe_close_pair(exe_name_pipe);
 245                 pager_fallback();
 246                 /* not reached */
 247         }
 248
 249         /* Return in the parent */
 250         stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3);
 251         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 252                 stored_stdout = safe_close(stored_stdout);
 253                 return (void) log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 254         }
 255         stdout_redirected = true;
 256
 257         stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3);
 258         if (dup2(fd[1], STDERR_FILENO) < 0) {
 259                 stored_stderr = safe_close(stored_stderr);
 260                 return (void) log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 261         }
 262         stderr_redirected = true;
 263
 264         exe_name_pipe[1] = safe_close(exe_name_pipe[1]);
 265
 266         r = no_quit_on_interrupt(TAKE_FD(exe_name_pipe[0]), less_opts);
 267         if (r > 0)
 268                 (void) ignore_signals(SIGINT);
 269 }
 270
 271 void pager_close(void) {
 272
 273         if (pager_pid <= 0)
 274                 return;
 275
 276         /* Inform pager that we are done */
 277         (void) fflush(stdout);
 278         if (stdout_redirected)
 279                 if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0)
 280                         (void) close(STDOUT_FILENO);
 281         stored_stdout = safe_close(stored_stdout);
 282         (void) fflush(stderr);
 283         if (stderr_redirected)
 284                 if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0)
 285                         (void) close(STDERR_FILENO);
 286         stored_stderr = safe_close(stored_stderr);
 287         stdout_redirected = stderr_redirected = false;
 288
 289         (void) kill(pager_pid, SIGCONT);
 290         (void) wait_for_terminate(TAKE_PID(pager_pid), NULL);
 291         pager_pid = 0;
 292 }
 293
 294 bool pager_have(void) {
 295         return pager_pid > 0;
 296 }
 297
 298 int show_man_page(const char *desc, bool null_stdio) {
 299         const char *args[4] = { "man", NULL, NULL, NULL };
 300         char *e = NULL;
 301         pid_t pid;
 302         size_t k;
 303         int r;
 304
 305         k = strlen(desc);
 306
 307         if (desc[k-1] == ')')
 308                 e = strrchr(desc, '(');
 309
 310         if (e) {
 311                 char *page = NULL, *section = NULL;
 312
 313                 page = strndupa_safe(desc, e - desc);
 314                 section = strndupa_safe(e + 1, desc + k - e - 2);
 315
 316                 args[1] = section;
 317                 args[2] = page;
 318         } else
 319                 args[1] = desc;
 320
 321         r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG|(null_stdio ? FORK_NULL_STDIO : 0)|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
 322         if (r < 0)
 323                 return r;
 324         if (r == 0) {
 325                 /* Child */
 326                 execvp(args[0], (char**) args);
 327                 log_error_errno(errno, "Failed to execute man: %m");
 328                 _exit(EXIT_FAILURE);
 329         }
 330
 331         return wait_for_terminate_and_check(NULL, pid, 0);
 332 }