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, const void *, size_t);
43 static int (*real_close)(int);
44 static size_t (*real_fwrite)(const void *, 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();
69 if (tracked_fds_count == 0) {
73 /* Never touch anything not going to a terminal - unless we are explicitly
75 if (!force_write_to_non_tty && !isatty(fd)) {
79 return tracked_fds_find(fd);
82 static void dup_fd(int oldfd, int newfd) {
84 debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
88 init_from_environment();
90 if (tracked_fds_count == 0) {
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();
115 if (tracked_fds_count == 0) {
119 tracked_fds_remove(fd);
123 /* "Action" handlers called when a file descriptor is matched. */
125 static char *pre_string;
126 static size_t pre_string_size;
127 static char *post_string;
128 static size_t post_string_size;
130 /* Load alternative pre/post strings from the environment if available, fall
131 * back to default values. */
132 inline static void init_pre_post_string() {
133 pre_string = getenv(ENV_NAME_PRE_STRING);
135 pre_string = DEFAULT_PRE_STRING;
137 pre_string_size = strlen(pre_string);
139 post_string = getenv(ENV_NAME_POST_STRING);
141 post_string = DEFAULT_POST_STRING;
143 post_string_size = strlen(post_string);
146 static void handle_fd_pre(int fd, int action) {
149 if (!pre_string || !post_string) {
150 init_pre_post_string();
153 DLSYM_FUNCTION(real_write, "write");
154 real_write(fd, pre_string, pre_string_size);
156 static void handle_fd_post(int fd, int action) {
159 /* write() already loaded above in handle_fd_pre(). */
160 real_write(fd, post_string, post_string_size);
163 static void handle_file_pre(FILE *stream, int action) {
166 if (!pre_string || !post_string) {
167 init_pre_post_string();
170 DLSYM_FUNCTION(real_fwrite, "fwrite");
171 real_fwrite(pre_string, pre_string_size, 1, stream);
173 static void handle_file_post(FILE *stream, int action) {
176 /* fwrite() already loaded above in handle_file_pre(). */
177 real_fwrite(post_string, post_string_size, 1, stream);
182 /* Hook all important output functions to manipulate their output. */
184 HOOK_FD3(ssize_t, write, fd,
185 int, fd, const void *, buf, size_t, count)
186 HOOK_FILE4(size_t, fwrite, stream,
187 const void *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
190 HOOK_FILE2(int, fputs, stream,
191 const char *, s, FILE *, stream)
192 HOOK_FILE2(int, fputc, stream,
193 int, c, FILE *, stream)
194 HOOK_FILE2(int, putc, stream,
195 int, c, FILE *, stream)
196 HOOK_FILE1(int, putchar, stdout,
198 HOOK_FILE1(int, puts, stdout,
201 /* printf(3), excluding all s*() and vs*() functions (no output) */
202 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
203 const char *, format)
204 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
205 FILE *, stream, const char *, format)
206 HOOK_FILE2(int, vprintf, stdout,
207 const char *, format, va_list, ap)
208 HOOK_FILE3(int, vfprintf, stream,
209 FILE *, stream, const char *, format, va_list, ap)
210 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
211 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
212 int, flag, const char *, format)
213 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
214 FILE *, fp, int, flag, const char *, format)
215 HOOK_FILE3(int, __vprintf_chk, stdout,
216 int, flag, const char *, format, va_list, ap)
217 HOOK_FILE4(int, __vfprintf_chk, stream,
218 FILE *, stream, int, flag, const char *, format, va_list, ap)
220 /* unlocked_stdio(3), only functions from above are hooked */
221 HOOK_FILE4(size_t, fwrite_unlocked, stream,
222 const void *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
223 HOOK_FILE2(int, fputs_unlocked, stream,
224 const char *, s, FILE *, stream)
225 HOOK_FILE2(int, fputc_unlocked, stream,
226 int, c, FILE *, stream)
227 HOOK_FILE2(int, putc_unlocked, stream,
228 int, c, FILE *, stream)
229 HOOK_FILE1(int, putchar_unlocked, stdout,
231 HOOK_FILE1(int, puts_unlocked, stdout,
235 HOOK_VOID1(void, perror, STDERR_FILENO,
240 static void error_vararg(int status, int errnum,
241 const char *filename, unsigned int linenum,
242 const char *format, va_list ap) {
243 static const char *last_filename;
244 static unsigned int last_linenum;
246 /* Skip this error message if requested and if there was already an error
247 * in the same file/line. */
248 if (error_one_per_line
249 && filename != NULL && linenum != 0
250 && filename == last_filename && linenum == last_linenum) {
253 last_filename = filename;
254 last_linenum = linenum;
256 error_message_count++;
260 if (error_print_progname) {
261 error_print_progname();
263 fprintf(stderr, "%s:", program_invocation_name);
265 if (filename != NULL && linenum != 0) {
266 fprintf(stderr, "%s:%u:", filename, linenum);
267 if (error_print_progname) {
268 fprintf(stderr, " ");
271 if (!error_print_progname) {
272 fprintf(stderr, " ");
276 vfprintf(stderr, format, ap);
279 fprintf(stderr, ": %s", strerror(errnum));
282 fprintf(stderr, "\n");
288 void error_at_line(int status, int errnum,
289 const char *filename, unsigned int linenum,
290 const char *format, ...) {
293 va_start(ap, format);
294 error_vararg(status, errnum, filename, linenum, format, ap);
297 void error(int status, int errnum, const char *format, ...) {
300 va_start(ap, format);
301 error_vararg(status, errnum, NULL, 0, format, ap);
307 /* Hook functions which duplicate file descriptors to track them. */
309 static int (*real_dup)(int);
310 static int (*real_dup2)(int, int);
311 static int (*real_dup3)(int, int, int);
315 DLSYM_FUNCTION(real_dup, "dup");
317 newfd = real_dup(oldfd);
319 int saved_errno = errno;
320 dup_fd(oldfd, newfd);
326 int dup2(int oldfd, int newfd) {
327 DLSYM_FUNCTION(real_dup2, "dup2");
329 newfd = real_dup2(oldfd, newfd);
331 int saved_errno = errno;
332 dup_fd(oldfd, newfd);
338 int dup3(int oldfd, int newfd, int flags) {
339 DLSYM_FUNCTION(real_dup3, "dup3");
341 newfd = real_dup3(oldfd, newfd, flags);
343 int saved_errno = errno;
344 dup_fd(oldfd, newfd);
351 static int (*real_fcntl)(int, int, ...);
352 int fcntl(int fd, int cmd, ...) {
356 DLSYM_FUNCTION(real_fcntl, "fcntl");
358 /* fcntl() takes different types of arguments depending on the cmd type
359 * (int, void and pointers are used at the moment). Handling these
360 * arguments for different systems and with possible changes in the future
363 * Therefore always retrieve a void-pointer from our arguments (even if it
364 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
365 * problems because a void-pointer is most-likely bigger than an int
366 * (something which is not true in reverse) and shouldn't cause
367 * truncation. For register based calling conventions an invalid register
368 * content is passed, but ignored by real_fcntl(). Not perfect, but should
372 result = real_fcntl(fd, cmd, va_arg(ap, void *));
375 /* We only care about duping fds. */
376 if (cmd == F_DUPFD && result != -1) {
377 int saved_errno = errno;
385 static int (*real_close)(int);
387 DLSYM_FUNCTION(real_close, "close");
390 return real_close(fd);
392 static int (*real_fclose)(FILE *);
393 int fclose(FILE *fp) {
394 DLSYM_FUNCTION(real_fclose, "fclose");
396 close_fd(fileno(fp));
397 return real_fclose(fp);
401 /* Hook functions which are necessary for correct tracking. */
403 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
405 /* vfork() is similar to fork() but the address space is shared between
406 * father and child. It's designed for fork()/exec() usage because it's
407 * faster than fork(). However according to the POSIX standard the "child"
408 * isn't allowed to perform any memory-modifications before the exec()
409 * (except the pid_t result variable of vfork()).
411 * As some programs don't adhere to the standard (e.g. the "child" closes
412 * or dups a descriptor before the exec()) and this breaks our tracking of
413 * file descriptors (e.g. it gets closed in the parent as well), we just
414 * fork() instead. This is in compliance with the POSIX standard and as
415 * most systems use copy-on-write anyway not a performance issue. */
421 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
422 * a custom environment which doesn't necessarily contain our updates to
423 * ENV_NAME_FDS. It's also faster to update the environment only when
424 * necessary, right before the exec() to pass it to the new process. */
426 static int (*real_execve)(const char *filename, char *const argv[], char *const env[]);
427 int execve(const char *filename, char *const argv[], char *const env[]) {
428 DLSYM_FUNCTION(real_execve, "execve");
433 /* Count arguments and search for existing ENV_NAME_FDS environment
436 char * const *x = env;
438 if (!strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
446 /* Terminating NULL. */
449 char *env_copy[count + 1 /* space for our new entry if necessary */];
450 memcpy(env_copy, env, count * sizeof(char *));
452 /* Make sure the information from the environment is loaded. We can't just
453 * do nothing (like update_environment()) because the caller might pass a
454 * different environment which doesn't include any of our settings. */
456 init_from_environment();
459 char fds_env[strlen(ENV_NAME_FDS) + 1 + update_environment_buffer_size()];
460 strcpy(fds_env, ENV_NAME_FDS "=");
461 update_environment_buffer(fds_env + strlen(ENV_NAME_FDS) + 1);
464 env_copy[index] = fds_env;
466 /* If the process removed ENV_NAME_FDS from the environment, re-add
468 env_copy[count-1] = fds_env;
469 env_copy[count] = NULL;
472 return real_execve(filename, argv, env_copy);
475 #define EXECL_COPY_VARARGS_START(args) \
479 /* Count arguments. */ \
480 size_t count = 1; /* arg */ \
482 while (va_arg(ap, const char *)) { \
487 /* Copy varargs. */ \
488 char *args[count + 1 /* terminating NULL */]; \
489 args[0] = (char *)arg; \
493 while ((x = va_arg(ap, char *))) { \
497 #define EXECL_COPY_VARARGS_END(args) \
499 #define EXECL_COPY_VARARGS(args) \
500 EXECL_COPY_VARARGS_START(args); \
501 EXECL_COPY_VARARGS_END(args);
503 int execl(const char *path, const char *arg, ...) {
504 EXECL_COPY_VARARGS(args);
506 update_environment();
507 return execv(path, args);
510 int execlp(const char *file, const char *arg, ...) {
511 EXECL_COPY_VARARGS(args);
513 update_environment();
514 return execvp(file, args);
517 int execle(const char *path, const char *arg, ... /*, char *const envp[] */) {
518 EXECL_COPY_VARARGS_START(args);
519 /* Get envp[] located after arguments. */
520 char * const *envp = va_arg(ap, char * const *);
521 EXECL_COPY_VARARGS_END(args);
523 return execve(path, args, envp);
526 static int (*real_execv)(const char *path, char *const argv[]);
527 int execv(const char *path, char *const argv[]) {
528 DLSYM_FUNCTION(real_execv, "execv");
530 update_environment();
531 return real_execv(path, argv);
534 static int (*real_execvp)(const char *path, char *const argv[]);
535 int execvp(const char *path, char *const argv[]) {
536 DLSYM_FUNCTION(real_execvp, "execvp");
538 update_environment();
539 return real_execvp(path, argv);