2 * Hook output functions (like printf(3)) with LD_PRELOAD to color stderr (or
3 * other file descriptors).
5 * Copyright (C) 2013 Simon Ruderich
7 * This program is free software: you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation, either version 3 of the License, or
10 * (at your option) any later version.
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
17 * You should have received a copy of the GNU General Public License
18 * along with this program. If not, see <http://www.gnu.org/licenses/>.
23 /* Must be loaded before the following headers. */
24 #include "ldpreload.h"
37 /* Conflicting declaration in glibc. */
38 #undef fwrite_unlocked
41 /* Used by various functions, including debug(). */
42 static ssize_t (*real_write)(int, void const *, size_t);
43 static int (*real_close)(int);
44 static size_t (*real_fwrite)(void const *, size_t, size_t, FILE *);
46 /* Did we already (try to) parse the environment and setup the necessary
48 static int initialized;
49 /* Force hooked writes even when not writing to a tty. Used for tests. */
50 static int force_write_to_non_tty;
53 #include "constants.h"
58 #include "hookmacros.h"
63 /* Should the "action" handler be invoked for this file descriptor? */
64 static int check_handle_fd(int fd) {
65 /* Load state from environment. Only necessary once per process. */
67 init_from_environment();
70 /* tracked_fds_find() is most likely faster than calling isatty(),
71 * therefore check if we are tracking this file descriptor first. */
72 if (!tracked_fds_find(fd)) {
76 /* Never touch anything not going to a terminal - unless we are explicitly
78 if (force_write_to_non_tty) {
82 int saved_errno = errno;
83 int result = isatty(fd);
89 static void dup_fd(int oldfd, int newfd) {
91 debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
95 init_from_environment();
98 /* We are already tracking this file descriptor, add newfd to the list as
99 * it will reference the same descriptor. */
100 if (tracked_fds_find(oldfd)) {
101 if (!tracked_fds_find(newfd)) {
102 tracked_fds_add(newfd);
104 /* We are not tracking this file descriptor, remove newfd from the list
107 tracked_fds_remove(newfd);
111 static void close_fd(int fd) {
113 debug("%3d -> .\t\t\t[%d]\n", fd, getpid());
117 init_from_environment();
120 tracked_fds_remove(fd);
124 /* "Action" handlers called when a file descriptor is matched. */
126 static char const *pre_string;
127 static size_t pre_string_size;
128 static char const *post_string;
129 static size_t post_string_size;
131 /* Load alternative pre/post strings from the environment if available, fall
132 * back to default values. */
133 inline static void init_pre_post_string(void) {
134 pre_string = getenv(ENV_NAME_PRE_STRING);
136 pre_string = DEFAULT_PRE_STRING;
138 pre_string_size = strlen(pre_string);
140 post_string = getenv(ENV_NAME_POST_STRING);
142 post_string = DEFAULT_POST_STRING;
144 post_string_size = strlen(post_string);
147 static void handle_fd_pre(int fd) {
148 int saved_errno = errno;
150 if (!pre_string || !post_string) {
151 init_pre_post_string();
154 DLSYM_FUNCTION(real_write, "write");
155 real_write(fd, pre_string, pre_string_size);
159 static void handle_fd_post(int fd) {
160 int saved_errno = errno;
162 /* write() already loaded above in handle_fd_pre(). */
163 real_write(fd, post_string, post_string_size);
168 static void handle_file_pre(FILE *stream) {
169 int saved_errno = errno;
171 if (!pre_string || !post_string) {
172 init_pre_post_string();
175 DLSYM_FUNCTION(real_fwrite, "fwrite");
176 real_fwrite(pre_string, pre_string_size, 1, stream);
180 static void handle_file_post(FILE *stream) {
181 int saved_errno = errno;
183 /* fwrite() already loaded above in handle_file_pre(). */
184 real_fwrite(post_string, post_string_size, 1, stream);
191 /* Hook all important output functions to manipulate their output. */
193 HOOK_FD3(ssize_t, write, fd,
194 int, fd, void const *, buf, size_t, count)
195 HOOK_FILE4(size_t, fwrite, stream,
196 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
199 HOOK_FILE2(int, fputs, stream,
200 char const *, s, FILE *, stream)
201 HOOK_FILE2(int, fputc, stream,
202 int, c, FILE *, stream)
203 HOOK_FILE2(int, putc, stream,
204 int, c, FILE *, stream)
205 HOOK_FILE1(int, putchar, stdout,
207 HOOK_FILE1(int, puts, stdout,
210 /* printf(3), excluding all s*() and vs*() functions (no output) */
211 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
212 char const *, format)
213 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
214 FILE *, stream, char const *, format)
215 HOOK_FILE2(int, vprintf, stdout,
216 char const *, format, va_list, ap)
217 HOOK_FILE3(int, vfprintf, stream,
218 FILE *, stream, char const *, format, va_list, ap)
219 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
220 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
221 int, flag, char const *, format)
222 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
223 FILE *, fp, int, flag, char const *, format)
224 HOOK_FILE3(int, __vprintf_chk, stdout,
225 int, flag, char const *, format, va_list, ap)
226 HOOK_FILE4(int, __vfprintf_chk, stream,
227 FILE *, stream, int, flag, char const *, format, va_list, ap)
229 /* unlocked_stdio(3), only functions from above are hooked */
230 HOOK_FILE4(size_t, fwrite_unlocked, stream,
231 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
232 HOOK_FILE2(int, fputs_unlocked, stream,
233 char const *, s, FILE *, stream)
234 HOOK_FILE2(int, fputc_unlocked, stream,
235 int, c, FILE *, stream)
236 HOOK_FILE2(int, putc_unlocked, stream,
237 int, c, FILE *, stream)
238 HOOK_FILE1(int, putchar_unlocked, stdout,
242 HOOK_VOID1(void, perror, STDERR_FILENO,
247 static void error_vararg(int status, int errnum,
248 char const *filename, unsigned int linenum,
249 char const *format, va_list ap) {
250 static char const *last_filename;
251 static unsigned int last_linenum;
253 /* Skip this error message if requested and if there was already an error
254 * in the same file/line. */
255 if (error_one_per_line
256 && filename != NULL && linenum != 0
257 && filename == last_filename && linenum == last_linenum) {
260 last_filename = filename;
261 last_linenum = linenum;
263 error_message_count++;
267 if (error_print_progname) {
268 error_print_progname();
270 fprintf(stderr, "%s:", program_invocation_name);
272 if (filename != NULL && linenum != 0) {
273 fprintf(stderr, "%s:%u:", filename, linenum);
274 if (error_print_progname) {
275 fprintf(stderr, " ");
278 if (!error_print_progname) {
279 fprintf(stderr, " ");
283 vfprintf(stderr, format, ap);
286 fprintf(stderr, ": %s", strerror(errnum));
289 fprintf(stderr, "\n");
295 void error_at_line(int status, int errnum,
296 char const *filename, unsigned int linenum,
297 char const *format, ...) {
300 va_start(ap, format);
301 error_vararg(status, errnum, filename, linenum, format, ap);
304 void error(int status, int errnum, char const *format, ...) {
307 va_start(ap, format);
308 error_vararg(status, errnum, NULL, 0, format, ap);
314 /* Hook functions which duplicate file descriptors to track them. */
316 static int (*real_dup)(int);
317 static int (*real_dup2)(int, int);
318 static int (*real_dup3)(int, int, int);
322 DLSYM_FUNCTION(real_dup, "dup");
324 newfd = real_dup(oldfd);
326 dup_fd(oldfd, newfd);
331 int dup2(int oldfd, int newfd) {
332 DLSYM_FUNCTION(real_dup2, "dup2");
334 newfd = real_dup2(oldfd, newfd);
336 dup_fd(oldfd, newfd);
341 int dup3(int oldfd, int newfd, int flags) {
342 DLSYM_FUNCTION(real_dup3, "dup3");
344 newfd = real_dup3(oldfd, newfd, flags);
346 dup_fd(oldfd, newfd);
352 static int (*real_fcntl)(int, int, ...);
353 int fcntl(int fd, int cmd, ...) {
357 DLSYM_FUNCTION(real_fcntl, "fcntl");
359 /* fcntl() takes different types of arguments depending on the cmd type
360 * (int, void and pointers are used at the moment). Handling these
361 * arguments for different systems and with possible changes in the future
364 * Therefore always retrieve a void-pointer from our arguments (even if it
365 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
366 * problems because a void-pointer is most-likely bigger than an int
367 * (something which is not true in reverse) and shouldn't cause
368 * truncation. For register based calling conventions an invalid register
369 * content is passed, but ignored by real_fcntl(). Not perfect, but should
373 result = real_fcntl(fd, cmd, va_arg(ap, void *));
376 /* We only care about duping fds. */
377 if (cmd == F_DUPFD && result != -1) {
384 static int (*real_close)(int);
386 DLSYM_FUNCTION(real_close, "close");
389 return real_close(fd);
391 static int (*real_fclose)(FILE *);
392 int fclose(FILE *fp) {
393 DLSYM_FUNCTION(real_fclose, "fclose");
395 close_fd(fileno(fp));
396 return real_fclose(fp);
400 /* Hook functions which are necessary for correct tracking. */
402 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
404 /* vfork() is similar to fork() but the address space is shared between
405 * father and child. It's designed for fork()/exec() usage because it's
406 * faster than fork(). However according to the POSIX standard the "child"
407 * isn't allowed to perform any memory-modifications before the exec()
408 * (except the pid_t result variable of vfork()).
410 * As some programs don't adhere to the standard (e.g. the "child" closes
411 * or dups a descriptor before the exec()) and this breaks our tracking of
412 * file descriptors (e.g. it gets closed in the parent as well), we just
413 * fork() instead. This is in compliance with the POSIX standard and as
414 * most systems use copy-on-write anyway not a performance issue. */
420 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
421 * a custom environment which doesn't necessarily contain our updates to
422 * ENV_NAME_FDS. It's also faster to update the environment only when
423 * necessary, right before the exec() to pass it to the new process. */
425 static int (*real_execve)(char const *filename, char * const argv[], char * const env[]);
426 int execve(char const *filename, char * const argv[], char * const env[]) {
427 DLSYM_FUNCTION(real_execve, "execve");
432 /* Count arguments and search for existing ENV_NAME_FDS environment
435 char * const *x = env;
437 if (!strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
445 /* Terminating NULL. */
448 char *env_copy[count + 1 /* space for our new entry if necessary */];
449 memcpy(env_copy, env, count * sizeof(char *));
451 /* Make sure the information from the environment is loaded. We can't just
452 * do nothing (like update_environment()) because the caller might pass a
453 * different environment which doesn't include any of our settings. */
455 init_from_environment();
458 char fds_env[strlen(ENV_NAME_FDS) + 1 + update_environment_buffer_size()];
459 strcpy(fds_env, ENV_NAME_FDS "=");
460 update_environment_buffer(fds_env + strlen(ENV_NAME_FDS) + 1);
463 env_copy[index] = fds_env;
465 /* If the process removed ENV_NAME_FDS from the environment, re-add
467 env_copy[count-1] = fds_env;
468 env_copy[count] = NULL;
471 return real_execve(filename, argv, env_copy);
474 #define EXECL_COPY_VARARGS_START(args) \
478 /* Count arguments. */ \
479 size_t count = 1; /* arg */ \
481 while (va_arg(ap, char const *)) { \
486 /* Copy varargs. */ \
487 char *args[count + 1 /* terminating NULL */]; \
488 args[0] = (char *)arg; \
492 while ((x = va_arg(ap, char *))) { \
496 #define EXECL_COPY_VARARGS_END(args) \
498 #define EXECL_COPY_VARARGS(args) \
499 EXECL_COPY_VARARGS_START(args); \
500 EXECL_COPY_VARARGS_END(args);
502 int execl(char const *path, char const *arg, ...) {
503 EXECL_COPY_VARARGS(args);
505 update_environment();
506 return execv(path, args);
509 int execlp(char const *file, char const *arg, ...) {
510 EXECL_COPY_VARARGS(args);
512 update_environment();
513 return execvp(file, args);
516 int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
517 EXECL_COPY_VARARGS_START(args);
518 /* Get envp[] located after arguments. */
519 char * const *envp = va_arg(ap, char * const *);
520 EXECL_COPY_VARARGS_END(args);
522 return execve(path, args, envp);
525 static int (*real_execv)(char const *path, char * const argv[]);
526 int execv(char const *path, char * const argv[]) {
527 DLSYM_FUNCTION(real_execv, "execv");
529 update_environment();
530 return real_execv(path, argv);
533 static int (*real_execvp)(char const *path, char * const argv[]);
534 int execvp(char const *path, char * const argv[]) {
535 DLSYM_FUNCTION(real_execvp, "execvp");
537 update_environment();
538 return real_execvp(path, argv);