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 && !isatty(fd)) {
85 static void dup_fd(int oldfd, int newfd) {
87 debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
91 init_from_environment();
94 /* We are already tracking this file descriptor, add newfd to the list as
95 * it will reference the same descriptor. */
96 if (tracked_fds_find(oldfd)) {
97 if (!tracked_fds_find(newfd)) {
98 tracked_fds_add(newfd);
100 /* We are not tracking this file descriptor, remove newfd from the list
103 tracked_fds_remove(newfd);
107 static void close_fd(int fd) {
109 debug("%3d -> .\t\t\t[%d]\n", fd, getpid());
113 init_from_environment();
116 tracked_fds_remove(fd);
120 /* "Action" handlers called when a file descriptor is matched. */
122 static char const *pre_string;
123 static size_t pre_string_size;
124 static char const *post_string;
125 static size_t post_string_size;
127 /* Load alternative pre/post strings from the environment if available, fall
128 * back to default values. */
129 inline static void init_pre_post_string(void) {
130 pre_string = getenv(ENV_NAME_PRE_STRING);
132 pre_string = DEFAULT_PRE_STRING;
134 pre_string_size = strlen(pre_string);
136 post_string = getenv(ENV_NAME_POST_STRING);
138 post_string = DEFAULT_POST_STRING;
140 post_string_size = strlen(post_string);
143 static void handle_fd_pre(int fd, int action) {
146 if (!pre_string || !post_string) {
147 init_pre_post_string();
150 DLSYM_FUNCTION(real_write, "write");
151 real_write(fd, pre_string, pre_string_size);
153 static void handle_fd_post(int fd, int action) {
156 /* write() already loaded above in handle_fd_pre(). */
157 real_write(fd, post_string, post_string_size);
160 static void handle_file_pre(FILE *stream, int action) {
163 if (!pre_string || !post_string) {
164 init_pre_post_string();
167 DLSYM_FUNCTION(real_fwrite, "fwrite");
168 real_fwrite(pre_string, pre_string_size, 1, stream);
170 static void handle_file_post(FILE *stream, int action) {
173 /* fwrite() already loaded above in handle_file_pre(). */
174 real_fwrite(post_string, post_string_size, 1, stream);
179 /* Hook all important output functions to manipulate their output. */
181 HOOK_FD3(ssize_t, write, fd,
182 int, fd, void const *, buf, size_t, count)
183 HOOK_FILE4(size_t, fwrite, stream,
184 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
187 HOOK_FILE2(int, fputs, stream,
188 char const *, s, FILE *, stream)
189 HOOK_FILE2(int, fputc, stream,
190 int, c, FILE *, stream)
191 HOOK_FILE2(int, putc, stream,
192 int, c, FILE *, stream)
193 HOOK_FILE1(int, putchar, stdout,
195 HOOK_FILE1(int, puts, stdout,
198 /* printf(3), excluding all s*() and vs*() functions (no output) */
199 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
200 char const *, format)
201 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
202 FILE *, stream, char const *, format)
203 HOOK_FILE2(int, vprintf, stdout,
204 char const *, format, va_list, ap)
205 HOOK_FILE3(int, vfprintf, stream,
206 FILE *, stream, char const *, format, va_list, ap)
207 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
208 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
209 int, flag, char const *, format)
210 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
211 FILE *, fp, int, flag, char const *, format)
212 HOOK_FILE3(int, __vprintf_chk, stdout,
213 int, flag, char const *, format, va_list, ap)
214 HOOK_FILE4(int, __vfprintf_chk, stream,
215 FILE *, stream, int, flag, char const *, format, va_list, ap)
217 /* unlocked_stdio(3), only functions from above are hooked */
218 HOOK_FILE4(size_t, fwrite_unlocked, stream,
219 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
220 HOOK_FILE2(int, fputs_unlocked, stream,
221 char const *, s, FILE *, stream)
222 HOOK_FILE2(int, fputc_unlocked, stream,
223 int, c, FILE *, stream)
224 HOOK_FILE2(int, putc_unlocked, stream,
225 int, c, FILE *, stream)
226 HOOK_FILE1(int, putchar_unlocked, stdout,
228 HOOK_FILE1(int, puts_unlocked, stdout,
232 HOOK_VOID1(void, perror, STDERR_FILENO,
237 static void error_vararg(int status, int errnum,
238 char const *filename, unsigned int linenum,
239 char const *format, va_list ap) {
240 static char const *last_filename;
241 static unsigned int last_linenum;
243 /* Skip this error message if requested and if there was already an error
244 * in the same file/line. */
245 if (error_one_per_line
246 && filename != NULL && linenum != 0
247 && filename == last_filename && linenum == last_linenum) {
250 last_filename = filename;
251 last_linenum = linenum;
253 error_message_count++;
257 if (error_print_progname) {
258 error_print_progname();
260 fprintf(stderr, "%s:", program_invocation_name);
262 if (filename != NULL && linenum != 0) {
263 fprintf(stderr, "%s:%u:", filename, linenum);
264 if (error_print_progname) {
265 fprintf(stderr, " ");
268 if (!error_print_progname) {
269 fprintf(stderr, " ");
273 vfprintf(stderr, format, ap);
276 fprintf(stderr, ": %s", strerror(errnum));
279 fprintf(stderr, "\n");
285 void error_at_line(int status, int errnum,
286 char const *filename, unsigned int linenum,
287 char const *format, ...) {
290 va_start(ap, format);
291 error_vararg(status, errnum, filename, linenum, format, ap);
294 void error(int status, int errnum, char const *format, ...) {
297 va_start(ap, format);
298 error_vararg(status, errnum, NULL, 0, format, ap);
304 /* Hook functions which duplicate file descriptors to track them. */
306 static int (*real_dup)(int);
307 static int (*real_dup2)(int, int);
308 static int (*real_dup3)(int, int, int);
312 DLSYM_FUNCTION(real_dup, "dup");
314 newfd = real_dup(oldfd);
316 int saved_errno = errno;
317 dup_fd(oldfd, newfd);
323 int dup2(int oldfd, int newfd) {
324 DLSYM_FUNCTION(real_dup2, "dup2");
326 newfd = real_dup2(oldfd, newfd);
328 int saved_errno = errno;
329 dup_fd(oldfd, newfd);
335 int dup3(int oldfd, int newfd, int flags) {
336 DLSYM_FUNCTION(real_dup3, "dup3");
338 newfd = real_dup3(oldfd, newfd, flags);
340 int saved_errno = errno;
341 dup_fd(oldfd, newfd);
348 static int (*real_fcntl)(int, int, ...);
349 int fcntl(int fd, int cmd, ...) {
353 DLSYM_FUNCTION(real_fcntl, "fcntl");
355 /* fcntl() takes different types of arguments depending on the cmd type
356 * (int, void and pointers are used at the moment). Handling these
357 * arguments for different systems and with possible changes in the future
360 * Therefore always retrieve a void-pointer from our arguments (even if it
361 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
362 * problems because a void-pointer is most-likely bigger than an int
363 * (something which is not true in reverse) and shouldn't cause
364 * truncation. For register based calling conventions an invalid register
365 * content is passed, but ignored by real_fcntl(). Not perfect, but should
369 result = real_fcntl(fd, cmd, va_arg(ap, void *));
372 /* We only care about duping fds. */
373 if (cmd == F_DUPFD && result != -1) {
374 int saved_errno = errno;
382 static int (*real_close)(int);
384 DLSYM_FUNCTION(real_close, "close");
387 return real_close(fd);
389 static int (*real_fclose)(FILE *);
390 int fclose(FILE *fp) {
391 DLSYM_FUNCTION(real_fclose, "fclose");
393 close_fd(fileno(fp));
394 return real_fclose(fp);
398 /* Hook functions which are necessary for correct tracking. */
400 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
402 /* vfork() is similar to fork() but the address space is shared between
403 * father and child. It's designed for fork()/exec() usage because it's
404 * faster than fork(). However according to the POSIX standard the "child"
405 * isn't allowed to perform any memory-modifications before the exec()
406 * (except the pid_t result variable of vfork()).
408 * As some programs don't adhere to the standard (e.g. the "child" closes
409 * or dups a descriptor before the exec()) and this breaks our tracking of
410 * file descriptors (e.g. it gets closed in the parent as well), we just
411 * fork() instead. This is in compliance with the POSIX standard and as
412 * most systems use copy-on-write anyway not a performance issue. */
418 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
419 * a custom environment which doesn't necessarily contain our updates to
420 * ENV_NAME_FDS. It's also faster to update the environment only when
421 * necessary, right before the exec() to pass it to the new process. */
423 static int (*real_execve)(char const *filename, char * const argv[], char * const env[]);
424 int execve(char const *filename, char * const argv[], char * const env[]) {
425 DLSYM_FUNCTION(real_execve, "execve");
430 /* Count arguments and search for existing ENV_NAME_FDS environment
433 char * const *x = env;
435 if (!strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
443 /* Terminating NULL. */
446 char *env_copy[count + 1 /* space for our new entry if necessary */];
447 memcpy(env_copy, env, count * sizeof(char *));
449 /* Make sure the information from the environment is loaded. We can't just
450 * do nothing (like update_environment()) because the caller might pass a
451 * different environment which doesn't include any of our settings. */
453 init_from_environment();
456 char fds_env[strlen(ENV_NAME_FDS) + 1 + update_environment_buffer_size()];
457 strcpy(fds_env, ENV_NAME_FDS "=");
458 update_environment_buffer(fds_env + strlen(ENV_NAME_FDS) + 1);
461 env_copy[index] = fds_env;
463 /* If the process removed ENV_NAME_FDS from the environment, re-add
465 env_copy[count-1] = fds_env;
466 env_copy[count] = NULL;
469 return real_execve(filename, argv, env_copy);
472 #define EXECL_COPY_VARARGS_START(args) \
476 /* Count arguments. */ \
477 size_t count = 1; /* arg */ \
479 while (va_arg(ap, char const *)) { \
484 /* Copy varargs. */ \
485 char *args[count + 1 /* terminating NULL */]; \
486 args[0] = (char *)arg; \
490 while ((x = va_arg(ap, char *))) { \
494 #define EXECL_COPY_VARARGS_END(args) \
496 #define EXECL_COPY_VARARGS(args) \
497 EXECL_COPY_VARARGS_START(args); \
498 EXECL_COPY_VARARGS_END(args);
500 int execl(char const *path, char const *arg, ...) {
501 EXECL_COPY_VARARGS(args);
503 update_environment();
504 return execv(path, args);
507 int execlp(char const *file, char const *arg, ...) {
508 EXECL_COPY_VARARGS(args);
510 update_environment();
511 return execvp(file, args);
514 int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
515 EXECL_COPY_VARARGS_START(args);
516 /* Get envp[] located after arguments. */
517 char * const *envp = va_arg(ap, char * const *);
518 EXECL_COPY_VARARGS_END(args);
520 return execve(path, args, envp);
523 static int (*real_execv)(char const *path, char * const argv[]);
524 int execv(char const *path, char * const argv[]) {
525 DLSYM_FUNCTION(real_execv, "execv");
527 update_environment();
528 return real_execv(path, argv);
531 static int (*real_execvp)(char const *path, char * const argv[]);
532 int execvp(char const *path, char * const argv[]) {
533 DLSYM_FUNCTION(real_execvp, "execvp");
535 update_environment();
536 return real_execvp(path, argv);