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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 | int 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 | const char *pager, *less_opts; | |
90 | int r; | |
91 | ||
92 | if (flags & PAGER_DISABLE) | |
93 | return 0; | |
94 | ||
95 | if (pager_pid > 0) | |
96 | return 1; | |
97 | ||
98 | if (terminal_is_dumb()) | |
99 | return 0; | |
100 | ||
101 | if (!is_main_thread()) | |
102 | return log_error_errno(SYNTHETIC_ERRNO(EPERM), "Pager invoked from wrong thread."); | |
103 | ||
104 | pager = getenv("SYSTEMD_PAGER"); | |
105 | if (!pager) | |
106 | pager = getenv("PAGER"); | |
107 | ||
108 | if (pager) { | |
109 | pager_args = strv_split(pager, WHITESPACE); | |
110 | if (!pager_args) | |
111 | return log_oom(); | |
112 | ||
113 | /* If the pager is explicitly turned off, honour it */ | |
114 | if (strv_isempty(pager_args) || strv_equal(pager_args, STRV_MAKE("cat"))) | |
115 | return 0; | |
116 | } | |
117 | ||
118 | /* Determine and cache number of columns/lines before we spawn the pager so that we get the value from the | |
119 | * actual tty */ | |
120 | (void) columns(); | |
121 | (void) lines(); | |
122 | ||
123 | if (pipe2(fd, O_CLOEXEC) < 0) | |
124 | return log_error_errno(errno, "Failed to create pager pipe: %m"); | |
125 | ||
126 | /* This is a pipe to feed the name of the executed pager binary into the parent */ | |
127 | if (pipe2(exe_name_pipe, O_CLOEXEC) < 0) | |
128 | return log_error_errno(errno, "Failed to create exe_name pipe: %m"); | |
129 | ||
130 | /* Initialize a good set of less options */ | |
131 | less_opts = getenv("SYSTEMD_LESS"); | |
132 | if (!less_opts) | |
133 | less_opts = "FRSXMK"; | |
134 | if (flags & PAGER_JUMP_TO_END) | |
135 | less_opts = strjoina(less_opts, " +G"); | |
136 | ||
137 | /* We set SIGINT as PR_DEATHSIG signal here, to match the "K" parameter we set in $LESS, which enables SIGINT behaviour. */ | |
138 | r = safe_fork("(pager)", FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGINT|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pager_pid); | |
139 | if (r < 0) | |
140 | return r; | |
141 | if (r == 0) { | |
142 | const char *less_charset, *exe; | |
143 | ||
144 | /* In the child start the pager */ | |
145 | ||
146 | if (dup2(fd[0], STDIN_FILENO) < 0) { | |
147 | log_error_errno(errno, "Failed to duplicate file descriptor to STDIN: %m"); | |
148 | _exit(EXIT_FAILURE); | |
149 | } | |
150 | ||
151 | safe_close_pair(fd); | |
152 | ||
153 | if (setenv("LESS", less_opts, 1) < 0) { | |
154 | log_error_errno(errno, "Failed to set environment variable LESS: %m"); | |
155 | _exit(EXIT_FAILURE); | |
156 | } | |
157 | ||
158 | /* Initialize a good charset for less. This is particularly important if we output UTF-8 | |
159 | * characters. */ | |
160 | less_charset = getenv("SYSTEMD_LESSCHARSET"); | |
161 | if (!less_charset && is_locale_utf8()) | |
162 | less_charset = "utf-8"; | |
163 | if (less_charset && | |
164 | setenv("LESSCHARSET", less_charset, 1) < 0) { | |
165 | log_error_errno(errno, "Failed to set environment variable LESSCHARSET: %m"); | |
166 | _exit(EXIT_FAILURE); | |
167 | } | |
168 | ||
169 | /* People might invoke us from sudo, don't needlessly allow less to be a way to shell out | |
170 | * privileged stuff. If the user set $SYSTEMD_PAGERSECURE, trust their configuration of the | |
171 | * pager. If they didn't, use secure mode when under euid is changed. If $SYSTEMD_PAGERSECURE | |
172 | * wasn't explicitly set, and we autodetect the need for secure mode, only use the pager we | |
173 | * know to be good. */ | |
174 | int use_secure_mode = getenv_bool_secure("SYSTEMD_PAGERSECURE"); | |
175 | bool trust_pager = use_secure_mode >= 0; | |
176 | if (use_secure_mode == -ENXIO) { | |
177 | uid_t uid; | |
178 | ||
179 | r = sd_pid_get_owner_uid(0, &uid); | |
180 | if (r < 0) | |
181 | log_debug_errno(r, "sd_pid_get_owner_uid() failed, enabling pager secure mode: %m"); | |
182 | ||
183 | use_secure_mode = r < 0 || uid != geteuid(); | |
184 | ||
185 | } else if (use_secure_mode < 0) { | |
186 | log_warning_errno(use_secure_mode, "Unable to parse $SYSTEMD_PAGERSECURE, assuming true: %m"); | |
187 | use_secure_mode = true; | |
188 | } | |
189 | ||
190 | /* We generally always set variables used by less, even if we end up using a different pager. | |
191 | * They shouldn't hurt in any case, and ideally other pagers would look at them too. */ | |
192 | r = set_unset_env("LESSSECURE", use_secure_mode ? "1" : NULL, true); | |
193 | if (r < 0) { | |
194 | log_error_errno(r, "Failed to adjust environment variable LESSSECURE: %m"); | |
195 | _exit(EXIT_FAILURE); | |
196 | } | |
197 | ||
198 | if (trust_pager && pager_args) { /* The pager config might be set globally, and we cannot | |
199 | * know if the user adjusted it to be appropriate for the | |
200 | * secure mode. Thus, start the pager specified through | |
201 | * envvars only when $SYSTEMD_PAGERSECURE was explicitly set | |
202 | * as well. */ | |
203 | r = loop_write(exe_name_pipe[1], pager_args[0], strlen(pager_args[0]) + 1, false); | |
204 | if (r < 0) { | |
205 | log_error_errno(r, "Failed to write pager name to socket: %m"); | |
206 | _exit(EXIT_FAILURE); | |
207 | } | |
208 | ||
209 | execvp(pager_args[0], pager_args); | |
210 | log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno, | |
211 | "Failed to execute '%s', using fallback pagers: %m", pager_args[0]); | |
212 | } | |
213 | ||
214 | /* Debian's alternatives command for pagers is called 'pager'. Note that we do not call | |
215 | * sensible-pagers here, since that is just a shell script that implements a logic that is | |
216 | * similar to this one anyway, but is Debian-specific. */ | |
217 | FOREACH_STRING(exe, "pager", "less", "more") { | |
218 | /* Only less implements secure mode right now. */ | |
219 | if (use_secure_mode && !streq(exe, "less")) | |
220 | continue; | |
221 | ||
222 | r = loop_write(exe_name_pipe[1], exe, strlen(exe) + 1, false); | |
223 | if (r < 0) { | |
224 | log_error_errno(r, "Failed to write pager name to socket: %m"); | |
225 | _exit(EXIT_FAILURE); | |
226 | } | |
227 | execlp(exe, exe, NULL); | |
228 | log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_WARNING, errno, | |
229 | "Failed to execute '%s', using next fallback pager: %m", exe); | |
230 | } | |
231 | ||
232 | /* Our builtin is also very secure. */ | |
233 | r = loop_write(exe_name_pipe[1], "(built-in)", strlen("(built-in)") + 1, false); | |
234 | if (r < 0) { | |
235 | log_error_errno(r, "Failed to write pager name to socket: %m"); | |
236 | _exit(EXIT_FAILURE); | |
237 | } | |
238 | /* Close pipe to signal the parent to start sending data */ | |
239 | safe_close_pair(exe_name_pipe); | |
240 | pager_fallback(); | |
241 | /* not reached */ | |
242 | } | |
243 | ||
244 | /* Return in the parent */ | |
245 | stored_stdout = fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 3); | |
246 | if (dup2(fd[1], STDOUT_FILENO) < 0) { | |
247 | stored_stdout = safe_close(stored_stdout); | |
248 | return log_error_errno(errno, "Failed to duplicate pager pipe: %m"); | |
249 | } | |
250 | stdout_redirected = true; | |
251 | ||
252 | stored_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC, 3); | |
253 | if (dup2(fd[1], STDERR_FILENO) < 0) { | |
254 | stored_stderr = safe_close(stored_stderr); | |
255 | return log_error_errno(errno, "Failed to duplicate pager pipe: %m"); | |
256 | } | |
257 | stderr_redirected = true; | |
258 | ||
259 | exe_name_pipe[1] = safe_close(exe_name_pipe[1]); | |
260 | ||
261 | r = no_quit_on_interrupt(TAKE_FD(exe_name_pipe[0]), less_opts); | |
262 | if (r < 0) | |
263 | return r; | |
264 | if (r > 0) | |
265 | (void) ignore_signals(SIGINT); | |
266 | ||
267 | return 1; | |
268 | } | |
269 | ||
270 | void pager_close(void) { | |
271 | ||
272 | if (pager_pid <= 0) | |
273 | return; | |
274 | ||
275 | /* Inform pager that we are done */ | |
276 | (void) fflush(stdout); | |
277 | if (stdout_redirected) | |
278 | if (stored_stdout < 0 || dup2(stored_stdout, STDOUT_FILENO) < 0) | |
279 | (void) close(STDOUT_FILENO); | |
280 | stored_stdout = safe_close(stored_stdout); | |
281 | (void) fflush(stderr); | |
282 | if (stderr_redirected) | |
283 | if (stored_stderr < 0 || dup2(stored_stderr, STDERR_FILENO) < 0) | |
284 | (void) close(STDERR_FILENO); | |
285 | stored_stderr = safe_close(stored_stderr); | |
286 | stdout_redirected = stderr_redirected = false; | |
287 | ||
288 | (void) kill(pager_pid, SIGCONT); | |
289 | (void) wait_for_terminate(pager_pid, NULL); | |
290 | pager_pid = 0; | |
291 | } | |
292 | ||
293 | bool pager_have(void) { | |
294 | return pager_pid > 0; | |
295 | } | |
296 | ||
297 | int show_man_page(const char *desc, bool null_stdio) { | |
298 | const char *args[4] = { "man", NULL, NULL, NULL }; | |
299 | char *e = NULL; | |
300 | pid_t pid; | |
301 | size_t k; | |
302 | int r; | |
303 | ||
304 | k = strlen(desc); | |
305 | ||
306 | if (desc[k-1] == ')') | |
307 | e = strrchr(desc, '('); | |
308 | ||
309 | if (e) { | |
310 | char *page = NULL, *section = NULL; | |
311 | ||
312 | page = strndupa(desc, e - desc); | |
313 | section = strndupa(e + 1, desc + k - e - 2); | |
314 | ||
315 | args[1] = section; | |
316 | args[2] = page; | |
317 | } else | |
318 | args[1] = desc; | |
319 | ||
320 | r = safe_fork("(man)", FORK_RESET_SIGNALS|FORK_DEATHSIG|(null_stdio ? FORK_NULL_STDIO : 0)|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid); | |
321 | if (r < 0) | |
322 | return r; | |
323 | if (r == 0) { | |
324 | /* Child */ | |
325 | execvp(args[0], (char**) args); | |
326 | log_error_errno(errno, "Failed to execute man: %m"); | |
327 | _exit(EXIT_FAILURE); | |
328 | } | |
329 | ||
330 | return wait_for_terminate_and_check(NULL, pid, 0); | |
331 | } |