src/shared/pager.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6
   7 #include "sd-login.h"
   8
   9 #include "copy.h"
  10 #include "env-util.h"
  11 #include "fd-util.h"
  12 #include "fileio.h"
  13 #include "io-util.h"
  14 #include "locale-util.h"
  15 #include "log.h"
  16 #include "pager.h"
  17 #include "process-util.h"
  18 #include "signal-util.h"
  19 #include "string-util.h"
  20 #include "strv.h"
  21 #include "terminal-util.h"
  22
  23 static pid_t pager_pid = 0;
  24
  25 static int stored_stdout = -1;
  26 static int stored_stderr = -1;
  27 static bool stdout_redirected = false;
  28 static bool stderr_redirected = false;
  29
  30 _noreturn_ static void pager_fallback(void) {
  31         int r;
  32
  33         r = copy_bytes(STDIN_FILENO, STDOUT_FILENO, UINT64_MAX, 0);
  34         if (r < 0) {
  35                 log_error_errno(r, "Internal pager failed: %m");
  36                 _exit(EXIT_FAILURE);
  37         }
  38
  39         _exit(EXIT_SUCCESS);
  40 }
  41
  42 static int no_quit_on_interrupt(int exe_name_fd, const char *less_opts) {
  43         _cleanup_fclose_ FILE *file = NULL;
  44         _cleanup_free_ char *line = NULL;
  45         int r;
  46
  47         assert(exe_name_fd >= 0);
  48         assert(less_opts);
  49
  50         /* This takes ownership of exe_name_fd */
  51         file = fdopen(exe_name_fd, "r");
  52         if (!file) {
  53                 safe_close(exe_name_fd);
  54                 return log_error_errno(errno, "Failed to create FILE object: %m");
  55         }
  56
  57         /* Find the last line */
  58         for (;;) {
  59                 _cleanup_free_ char *t = NULL;
  60
  61                 r = read_line(file, LONG_LINE_MAX, &t);
  62                 if (r < 0)
  63                         return log_error_errno(r, "Failed to read from socket: %m");
  64                 if (r == 0)
  65                         break;
  66
  67                 free_and_replace(line, t);
  68         }
  69
  70         /* We only treat "less" specially.
  71          * Return true whenever option K is *not* set. */
  72         r = streq_ptr(line, "less") && !strchr(less_opts, 'K');
  73
  74         log_debug("Pager executable is \"%s\", options \"%s\", quit_on_interrupt: %s",
  75                   strnull(line), less_opts, yes_no(!r));
  76         return r;
  77 }
  78
  79 static bool running_with_escalated_privileges(void) {
  80         int r;
  81
  82         if (getenv("SUDO_UID"))
  83                 return true;
  84
  85         uid_t uid;
  86         r = sd_pid_get_owner_uid(0, &uid);
  87         if (r < 0) {
  88                 log_debug_errno(r, "sd_pid_get_owner_uid() failed, enabling pager secure mode: %m");
  89                 return true;
  90         }
  91
  92         return uid != geteuid();
  93 }
  94
  95 void pager_open(PagerFlags flags) {
  96         _cleanup_close_pair_ int fd[2] = EBADF_PAIR, exe_name_pipe[2] = EBADF_PAIR;
  97         _cleanup_strv_free_ char **pager_args = NULL;
  98         _cleanup_free_ char *l = NULL;
  99         const char *pager, *less_opts;
 100         int r;
 101
 102         if (flags & PAGER_DISABLE)
 103                 return;
 104
 105         if (pager_pid > 0)
 106                 return;
 107
 108         if (terminal_is_dumb())
 109                 return;
 110
 111         if (!is_main_thread())
 112                 return (void) log_error_errno(SYNTHETIC_ERRNO(EPERM), "Pager invoked from wrong thread.");
 113
 114         pager = getenv("SYSTEMD_PAGER");
 115         if (!pager)
 116                 pager = getenv("PAGER");
 117
 118         if (pager) {
 119                 pager_args = strv_split(pager, WHITESPACE);
 120                 if (!pager_args)
 121                         return (void) log_oom();
 122
 123                 /* If the pager is explicitly turned off, honour it */
 124                 if (strv_isempty(pager_args) || strv_equal(pager_args, STRV_MAKE("cat")))
 125                         return;
 126         }
 127
 128         /* Determine and cache number of columns/lines before we spawn the pager so that we get the value from the
 129          * actual tty */
 130         (void) columns();
 131         (void) lines();
 132
 133         if (pipe2(fd, O_CLOEXEC) < 0)
 134                 return (void) log_error_errno(errno, "Failed to create pager pipe: %m");
 135
 136         /* This is a pipe to feed the name of the executed pager binary into the parent */
 137         if (pipe2(exe_name_pipe, O_CLOEXEC) < 0)
 138                 return (void) log_error_errno(errno, "Failed to create exe_name pipe: %m");
 139
 140         /* Initialize a good set of less options */
 141         less_opts = getenv("SYSTEMD_LESS");
 142         if (!less_opts)
 143                 less_opts = "FRSXMK";
 144         if (flags & PAGER_JUMP_TO_END) {
 145                 l = strjoin(less_opts, " +G");
 146                 if (!l)
 147                         return (void) log_oom();
 148                 less_opts = l;
 149         }
 150
 151         /* We set SIGINT as PR_DEATHSIG signal here, to match the "K" parameter we set in $LESS, which enables SIGINT behaviour. */
 152         r = safe_fork("(pager)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGINT|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pager_pid);
 153         if (r < 0)
 154                 return;
 155         if (r == 0) {
 156                 const char *less_charset;
 157
 158                 /* In the child start the pager */
 159
 160                 if (dup2(fd[0], STDIN_FILENO) < 0) {
 161                         log_error_errno(errno, "Failed to duplicate file descriptor to STDIN: %m");
 162                         _exit(EXIT_FAILURE);
 163                 }
 164
 165                 safe_close_pair(fd);
 166
 167                 if (setenv("LESS", less_opts, 1) < 0) {
 168                         log_error_errno(errno, "Failed to set environment variable LESS: %m");
 169                         _exit(EXIT_FAILURE);
 170                 }
 171
 172                 /* Initialize a good charset for less. This is particularly important if we output UTF-8
 173                  * characters. */
 174                 less_charset = getenv("SYSTEMD_LESSCHARSET");
 175                 if (!less_charset && is_locale_utf8())
 176                         less_charset = "utf-8";
 177                 if (less_charset &&
 178                     setenv("LESSCHARSET", less_charset, 1) < 0) {
 179                         log_error_errno(errno, "Failed to set environment variable LESSCHARSET: %m");
 180                         _exit(EXIT_FAILURE);
 181                 }
 182
 183                 /* People might invoke us from sudo, don't needlessly allow less to be a way to shell out
 184                  * privileged stuff. If the user set $SYSTEMD_PAGERSECURE, trust their configuration of the
 185                  * pager. If they didn't, use secure mode when under euid is changed. If $SYSTEMD_PAGERSECURE
 186                  * wasn't explicitly set, and we autodetect the need for secure mode, only use the pager we
 187                  * know to be good. */
 188                 int use_secure_mode = secure_getenv_bool("SYSTEMD_PAGERSECURE");
 189                 bool trust_pager = use_secure_mode >= 0;
 190                 if (use_secure_mode == -ENXIO)
 191                         use_secure_mode = running_with_escalated_privileges();
 192                 else if (use_secure_mode < 0) {
 193                         log_warning_errno(use_secure_mode, "Unable to parse $SYSTEMD_PAGERSECURE, assuming true: %m");
 194                         use_secure_mode = true;
 195                 }
 196
 197                 /* We generally always set variables used by less, even if we end up using a different pager.
 198                  * They shouldn't hurt in any case, and ideally other pagers would look at them too. */
 199                 r = set_unset_env("LESSSECURE", use_secure_mode ? "1" : NULL, true);
 200                 if (r < 0) {
 201                         log_error_errno(r, "Failed to adjust environment variable LESSSECURE: %m");
 202                         _exit(EXIT_FAILURE);
 203                 }
 204
 205                 if (trust_pager && pager_args) { /* The pager config might be set globally, and we cannot
 206                                                   * know if the user adjusted it to be appropriate for the
 207                                                   * secure mode. Thus, start the pager specified through
 208                                                   * envvars only when $SYSTEMD_PAGERSECURE was explicitly set
 209                                                   * as well. */
 210                         r = loop_write(exe_name_pipe[1], pager_args[0], strlen(pager_args[0]) + 1);
 211                         if (r < 0) {
 212                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 213                                 _exit(EXIT_FAILURE);
 214                         }
 215
 216                         execvp(pager_args[0], pager_args);
 217                         log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 218                                        "Failed to execute '%s', using fallback pagers: %m", pager_args[0]);
 219                 }
 220
 221                 /* Debian's alternatives command for pagers is called 'pager'. Note that we do not call
 222                  * sensible-pagers here, since that is just a shell script that implements a logic that is
 223                  * similar to this one anyway, but is Debian-specific. */
 224                 static const char* pagers[] = { "pager", "less", "more", "(built-in)" };
 225
 226                 for (unsigned i = 0; i < ELEMENTSOF(pagers); i++) {
 227                         /* Only less (and our trivial fallback) implement secure mode right now. */
 228                         if (use_secure_mode && !STR_IN_SET(pagers[i], "less", "(built-in)"))
 229                                 continue;
 230
 231                         r = loop_write(exe_name_pipe[1], pagers[i], strlen(pagers[i]) + 1);
 232                         if (r < 0) {
 233                                 log_error_errno(r, "Failed to write pager name to socket: %m");
 234                                 _exit(EXIT_FAILURE);
 235                         }
 236
 237                         if (i < ELEMENTSOF(pagers) - 1) {
 238                                 execlp(pagers[i], pagers[i], NULL);
 239                                 log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno,
 240                                                "Failed to execute '%s', will try '%s' next: %m", pagers[i], pagers[i+1]);
 241                         } else {
 242                                 /* Close pipe to signal the parent to start sending data */
 243                                 safe_close_pair(exe_name_pipe);
 244                                 pager_fallback();
 245                                 assert_not_reached();
 246                         }
 247                 }
 248         }
 249
 250         /* Return in the parent */
 251         stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3);
 252         if (dup2(fd[1], STDOUT_FILENO) < 0) {
 253                 stored_stdout = safe_close(stored_stdout);
 254                 return (void) log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 255         }
 256         stdout_redirected = true;
 257
 258         stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3);
 259         if (dup2(fd[1], STDERR_FILENO) < 0) {
 260                 stored_stderr = safe_close(stored_stderr);
 261                 return (void) log_error_errno(errno, "Failed to duplicate pager pipe: %m");
 262         }
 263         stderr_redirected = true;
 264
 265         exe_name_pipe[1] = safe_close(exe_name_pipe[1]);
 266
 267         r = no_quit_on_interrupt(TAKE_FD(exe_name_pipe[0]), less_opts);
 268         if (r > 0)
 269                 (void) ignore_signals(SIGINT);
 270 }
 271
 272 void pager_close(void) {
 273
 274         if (pager_pid <= 0)
 275                 return;
 276
 277         /* Inform pager that we are done */
 278         (void) fflush(stdout);
 279         if (stdout_redirected)
 280                 if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0)
 281                         (void) close(STDOUT_FILENO);
 282         stored_stdout = safe_close(stored_stdout);
 283         (void) fflush(stderr);
 284         if (stderr_redirected)
 285                 if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0)
 286                         (void) close(STDERR_FILENO);
 287         stored_stderr = safe_close(stored_stderr);
 288         stdout_redirected = stderr_redirected = false;
 289
 290         (void) kill(pager_pid, SIGCONT);
 291         (void) wait_for_terminate(TAKE_PID(pager_pid), NULL);
 292         pager_pid = 0;
 293 }
 294
 295 bool pager_have(void) {
 296         return pager_pid > 0;
 297 }
 298
 299 int show_man_page(const char *desc, bool null_stdio) {
 300         const char *args[4] = { "man", NULL, NULL, NULL };
 301         char *e = NULL;
 302         pid_t pid;
 303         size_t k;
 304         int r;
 305
 306         k = strlen(desc);
 307
 308         if (desc[k-1] == ')')
 309                 e = strrchr(desc, '(');
 310
 311         if (e) {
 312                 char *page = NULL, *section = NULL;
 313
 314                 page = strndupa_safe(desc, e - desc);
 315                 section = strndupa_safe(e + 1, desc + k - e - 2);
 316
 317                 args[1] = section;
 318                 args[2] = page;
 319         } else
 320                 args[1] = desc;
 321
 322         r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGTERM|(null_stdio ? FORK_REARRANGE_STDIO : 0)|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
 323         if (r < 0)
 324                 return r;
 325         if (r == 0) {
 326                 /* Child */
 327                 execvp(args[0], (char**) args);
 328                 log_error_errno(errno, "Failed to execute man: %m");
 329                 _exit(EXIT_FAILURE);
 330         }
 331
 332         return wait_for_terminate_and_check(NULL, pid, 0);
 333 }