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) {
144 if (!pre_string || !post_string) {
145 init_pre_post_string();
148 DLSYM_FUNCTION(real_write, "write");
149 real_write(fd, pre_string, pre_string_size);
151 static void handle_fd_post(int fd) {
152 /* write() already loaded above in handle_fd_pre(). */
153 real_write(fd, post_string, post_string_size);
156 static void handle_file_pre(FILE *stream) {
157 if (!pre_string || !post_string) {
158 init_pre_post_string();
161 DLSYM_FUNCTION(real_fwrite, "fwrite");
162 real_fwrite(pre_string, pre_string_size, 1, stream);
164 static void handle_file_post(FILE *stream) {
165 /* fwrite() already loaded above in handle_file_pre(). */
166 real_fwrite(post_string, post_string_size, 1, stream);
171 /* Hook all important output functions to manipulate their output. */
173 HOOK_FD3(ssize_t, write, fd,
174 int, fd, void const *, buf, size_t, count)
175 HOOK_FILE4(size_t, fwrite, stream,
176 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
179 HOOK_FILE2(int, fputs, stream,
180 char const *, s, FILE *, stream)
181 HOOK_FILE2(int, fputc, stream,
182 int, c, FILE *, stream)
183 HOOK_FILE2(int, putc, stream,
184 int, c, FILE *, stream)
185 HOOK_FILE1(int, putchar, stdout,
187 HOOK_FILE1(int, puts, stdout,
190 /* printf(3), excluding all s*() and vs*() functions (no output) */
191 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
192 char const *, format)
193 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
194 FILE *, stream, char const *, format)
195 HOOK_FILE2(int, vprintf, stdout,
196 char const *, format, va_list, ap)
197 HOOK_FILE3(int, vfprintf, stream,
198 FILE *, stream, char const *, format, va_list, ap)
199 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
200 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
201 int, flag, char const *, format)
202 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
203 FILE *, fp, int, flag, char const *, format)
204 HOOK_FILE3(int, __vprintf_chk, stdout,
205 int, flag, char const *, format, va_list, ap)
206 HOOK_FILE4(int, __vfprintf_chk, stream,
207 FILE *, stream, int, flag, char const *, format, va_list, ap)
209 /* unlocked_stdio(3), only functions from above are hooked */
210 HOOK_FILE4(size_t, fwrite_unlocked, stream,
211 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
212 HOOK_FILE2(int, fputs_unlocked, stream,
213 char const *, s, FILE *, stream)
214 HOOK_FILE2(int, fputc_unlocked, stream,
215 int, c, FILE *, stream)
216 HOOK_FILE2(int, putc_unlocked, stream,
217 int, c, FILE *, stream)
218 HOOK_FILE1(int, putchar_unlocked, stdout,
222 HOOK_VOID1(void, perror, STDERR_FILENO,
227 static void error_vararg(int status, int errnum,
228 char const *filename, unsigned int linenum,
229 char const *format, va_list ap) {
230 static char const *last_filename;
231 static unsigned int last_linenum;
233 /* Skip this error message if requested and if there was already an error
234 * in the same file/line. */
235 if (error_one_per_line
236 && filename != NULL && linenum != 0
237 && filename == last_filename && linenum == last_linenum) {
240 last_filename = filename;
241 last_linenum = linenum;
243 error_message_count++;
247 if (error_print_progname) {
248 error_print_progname();
250 fprintf(stderr, "%s:", program_invocation_name);
252 if (filename != NULL && linenum != 0) {
253 fprintf(stderr, "%s:%u:", filename, linenum);
254 if (error_print_progname) {
255 fprintf(stderr, " ");
258 if (!error_print_progname) {
259 fprintf(stderr, " ");
263 vfprintf(stderr, format, ap);
266 fprintf(stderr, ": %s", strerror(errnum));
269 fprintf(stderr, "\n");
275 void error_at_line(int status, int errnum,
276 char const *filename, unsigned int linenum,
277 char const *format, ...) {
280 va_start(ap, format);
281 error_vararg(status, errnum, filename, linenum, format, ap);
284 void error(int status, int errnum, char const *format, ...) {
287 va_start(ap, format);
288 error_vararg(status, errnum, NULL, 0, format, ap);
294 /* Hook functions which duplicate file descriptors to track them. */
296 static int (*real_dup)(int);
297 static int (*real_dup2)(int, int);
298 static int (*real_dup3)(int, int, int);
302 DLSYM_FUNCTION(real_dup, "dup");
304 newfd = real_dup(oldfd);
306 int saved_errno = errno;
307 dup_fd(oldfd, newfd);
313 int dup2(int oldfd, int newfd) {
314 DLSYM_FUNCTION(real_dup2, "dup2");
316 newfd = real_dup2(oldfd, newfd);
318 int saved_errno = errno;
319 dup_fd(oldfd, newfd);
325 int dup3(int oldfd, int newfd, int flags) {
326 DLSYM_FUNCTION(real_dup3, "dup3");
328 newfd = real_dup3(oldfd, newfd, flags);
330 int saved_errno = errno;
331 dup_fd(oldfd, newfd);
338 static int (*real_fcntl)(int, int, ...);
339 int fcntl(int fd, int cmd, ...) {
343 DLSYM_FUNCTION(real_fcntl, "fcntl");
345 /* fcntl() takes different types of arguments depending on the cmd type
346 * (int, void and pointers are used at the moment). Handling these
347 * arguments for different systems and with possible changes in the future
350 * Therefore always retrieve a void-pointer from our arguments (even if it
351 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
352 * problems because a void-pointer is most-likely bigger than an int
353 * (something which is not true in reverse) and shouldn't cause
354 * truncation. For register based calling conventions an invalid register
355 * content is passed, but ignored by real_fcntl(). Not perfect, but should
359 result = real_fcntl(fd, cmd, va_arg(ap, void *));
362 /* We only care about duping fds. */
363 if (cmd == F_DUPFD && result != -1) {
364 int saved_errno = errno;
372 static int (*real_close)(int);
374 DLSYM_FUNCTION(real_close, "close");
377 return real_close(fd);
379 static int (*real_fclose)(FILE *);
380 int fclose(FILE *fp) {
381 DLSYM_FUNCTION(real_fclose, "fclose");
383 close_fd(fileno(fp));
384 return real_fclose(fp);
388 /* Hook functions which are necessary for correct tracking. */
390 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
392 /* vfork() is similar to fork() but the address space is shared between
393 * father and child. It's designed for fork()/exec() usage because it's
394 * faster than fork(). However according to the POSIX standard the "child"
395 * isn't allowed to perform any memory-modifications before the exec()
396 * (except the pid_t result variable of vfork()).
398 * As some programs don't adhere to the standard (e.g. the "child" closes
399 * or dups a descriptor before the exec()) and this breaks our tracking of
400 * file descriptors (e.g. it gets closed in the parent as well), we just
401 * fork() instead. This is in compliance with the POSIX standard and as
402 * most systems use copy-on-write anyway not a performance issue. */
408 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
409 * a custom environment which doesn't necessarily contain our updates to
410 * ENV_NAME_FDS. It's also faster to update the environment only when
411 * necessary, right before the exec() to pass it to the new process. */
413 static int (*real_execve)(char const *filename, char * const argv[], char * const env[]);
414 int execve(char const *filename, char * const argv[], char * const env[]) {
415 DLSYM_FUNCTION(real_execve, "execve");
420 /* Count arguments and search for existing ENV_NAME_FDS environment
423 char * const *x = env;
425 if (!strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
433 /* Terminating NULL. */
436 char *env_copy[count + 1 /* space for our new entry if necessary */];
437 memcpy(env_copy, env, count * sizeof(char *));
439 /* Make sure the information from the environment is loaded. We can't just
440 * do nothing (like update_environment()) because the caller might pass a
441 * different environment which doesn't include any of our settings. */
443 init_from_environment();
446 char fds_env[strlen(ENV_NAME_FDS) + 1 + update_environment_buffer_size()];
447 strcpy(fds_env, ENV_NAME_FDS "=");
448 update_environment_buffer(fds_env + strlen(ENV_NAME_FDS) + 1);
451 env_copy[index] = fds_env;
453 /* If the process removed ENV_NAME_FDS from the environment, re-add
455 env_copy[count-1] = fds_env;
456 env_copy[count] = NULL;
459 return real_execve(filename, argv, env_copy);
462 #define EXECL_COPY_VARARGS_START(args) \
466 /* Count arguments. */ \
467 size_t count = 1; /* arg */ \
469 while (va_arg(ap, char const *)) { \
474 /* Copy varargs. */ \
475 char *args[count + 1 /* terminating NULL */]; \
476 args[0] = (char *)arg; \
480 while ((x = va_arg(ap, char *))) { \
484 #define EXECL_COPY_VARARGS_END(args) \
486 #define EXECL_COPY_VARARGS(args) \
487 EXECL_COPY_VARARGS_START(args); \
488 EXECL_COPY_VARARGS_END(args);
490 int execl(char const *path, char const *arg, ...) {
491 EXECL_COPY_VARARGS(args);
493 update_environment();
494 return execv(path, args);
497 int execlp(char const *file, char const *arg, ...) {
498 EXECL_COPY_VARARGS(args);
500 update_environment();
501 return execvp(file, args);
504 int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
505 EXECL_COPY_VARARGS_START(args);
506 /* Get envp[] located after arguments. */
507 char * const *envp = va_arg(ap, char * const *);
508 EXECL_COPY_VARARGS_END(args);
510 return execve(path, args, envp);
513 static int (*real_execv)(char const *path, char * const argv[]);
514 int execv(char const *path, char * const argv[]) {
515 DLSYM_FUNCTION(real_execv, "execv");
517 update_environment();
518 return real_execv(path, argv);
521 static int (*real_execvp)(char const *path, char * const argv[]);
522 int execvp(char const *path, char * const argv[]) {
523 DLSYM_FUNCTION(real_execvp, "execvp");
525 update_environment();
526 return real_execvp(path, argv);