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/>.
25 /* Must be loaded before the following headers. */
26 #include "ldpreload.h"
28 /* Disable assert()s if not compiled with --enable-debug. */
48 #ifdef HAVE_STRUCT__IO_FILE__FILENO
52 /* The following functions may be macros. Undefine them or they cause build
53 * failures when used in our hook macros below. */
55 /* In glibc, real fwrite_unlocked() is called in macro. */
56 #ifdef HAVE_FWRITE_UNLOCKED
57 # undef fwrite_unlocked
59 /* In Clang when compiling with hardening flags (fortify) on Debian Wheezy. */
62 /* On FreeBSD (9.1), __swbuf() is used instead of these macros. */
67 # undef putchar_unlocked
71 /* Used by various functions, including debug(). */
72 static ssize_t (*real_write)(int, void const *, size_t);
73 static int (*real_close)(int);
74 static size_t (*real_fwrite)(void const *, size_t, size_t, FILE *);
76 /* Did we already (try to) parse the environment and setup the necessary
78 static int initialized;
79 /* Force hooked writes even when not writing to a tty. Used for tests. */
80 static int force_write_to_non_tty;
81 /* Was ENV_NAME_FDS found and used when init_from_environment() was called?
82 * This is not true if the process set it manually after initialization. */
83 static int used_fds_set_by_user;
84 /* Was any of our handle_*_pre()/handle_*_post() functions called recursively?
85 * If so don't print the pre/post string for the recursive calls. This is
86 * necessary on some systems (e.g. FreeBSD 9.1) which call multiple hooked
87 * functions while printing a string (e.g. a FILE * and a fd hook function is
89 static int handle_recursive;
92 #include "constants.h"
97 #include "hookmacros.h"
102 /* See hookmacros.h for the decision if a function call is colored. */
105 /* Prevent inlining into hook functions because it may increase the number of
106 * spilled registers unnecessarily. As it's not called very often accept the
107 * additional call. */
108 static int isatty_noinline(int fd) noinline;
109 static int isatty_noinline(int fd) {
112 int saved_errno = errno;
113 int result = isatty(fd);
120 static void dup_fd(int oldfd, int newfd) {
122 debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
125 assert(oldfd >= 0 && newfd >= 0);
127 if (unlikely(!initialized)) {
128 init_from_environment();
131 /* We are already tracking this file descriptor, add newfd to the list as
132 * it will reference the same descriptor. */
133 if (tracked_fds_find(oldfd)) {
134 if (!tracked_fds_find(newfd)) {
135 tracked_fds_add(newfd);
137 /* We are not tracking this file descriptor, remove newfd from the list
140 tracked_fds_remove(newfd);
144 static void close_fd(int fd) {
146 debug("%3d -> .\t\t\t[%d]\n", fd, getpid());
151 if (unlikely(!initialized)) {
152 init_from_environment();
155 tracked_fds_remove(fd);
159 /* "Action" handlers called when a file descriptor is matched. */
161 static char const *pre_string;
162 static size_t pre_string_size;
163 static char const *post_string;
164 static size_t post_string_size;
166 /* Load alternative pre/post strings from the environment if available, fall
167 * back to default values. */
168 static void init_pre_post_string(void) {
169 pre_string = getenv(ENV_NAME_PRE_STRING);
171 pre_string = DEFAULT_PRE_STRING;
173 pre_string_size = strlen(pre_string);
175 post_string = getenv(ENV_NAME_POST_STRING);
177 post_string = DEFAULT_POST_STRING;
179 post_string_size = strlen(post_string);
182 /* Don't inline any of the pre/post functions. Keep the hook function as small
183 * as possible for speed reasons. */
184 static void handle_fd_pre(int fd) noinline;
185 static void handle_fd_post(int fd) noinline;
186 static void handle_file_pre(FILE *stream) noinline;
187 static void handle_file_post(FILE *stream) noinline;
189 static void handle_fd_pre(int fd) {
190 if (handle_recursive++ > 0) {
194 int saved_errno = errno;
196 if (unlikely(!pre_string)) {
197 init_pre_post_string();
200 DLSYM_FUNCTION(real_write, "write");
201 real_write(fd, pre_string, pre_string_size);
205 static void handle_fd_post(int fd) {
206 if (--handle_recursive > 0) {
210 int saved_errno = errno;
212 /* write() already loaded above in handle_fd_pre(). */
213 real_write(fd, post_string, post_string_size);
218 static void handle_file_pre(FILE *stream) {
219 if (handle_recursive++ > 0) {
223 int saved_errno = errno;
225 if (unlikely(!pre_string)) {
226 init_pre_post_string();
229 DLSYM_FUNCTION(real_fwrite, "fwrite");
230 real_fwrite(pre_string, pre_string_size, 1, stream);
234 static void handle_file_post(FILE *stream) {
235 if (--handle_recursive > 0) {
239 int saved_errno = errno;
241 /* fwrite() already loaded above in handle_file_pre(). */
242 real_fwrite(post_string, post_string_size, 1, stream);
249 /* Hook all important output functions to manipulate their output. */
251 HOOK_FD3(ssize_t, write, fd,
252 int, fd, void const *, buf, size_t, count)
253 HOOK_FILE4(size_t, fwrite, stream,
254 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
257 HOOK_FILE2(int, fputs, stream,
258 char const *, s, FILE *, stream)
259 HOOK_FILE2(int, fputc, stream,
260 int, c, FILE *, stream)
261 HOOK_FILE2(int, putc, stream,
262 int, c, FILE *, stream)
263 /* The glibc uses a macro for putc() which expands to _IO_putc(). However
264 * sometimes the raw putc() is used as well, not sure why. Make sure to hook
268 HOOK_FILE2(int, putc, stream,
269 int, c, FILE *, stream)
271 HOOK_FILE1(int, putchar, stdout,
273 HOOK_FILE1(int, puts, stdout,
276 /* printf(3), excluding all s*() and vs*() functions (no output) */
277 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
278 char const *, format)
279 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
280 FILE *, stream, char const *, format)
281 HOOK_FILE2(int, vprintf, stdout,
282 char const *, format, va_list, ap)
283 HOOK_FILE3(int, vfprintf, stream,
284 FILE *, stream, char const *, format, va_list, ap)
285 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
286 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
287 int, flag, char const *, format)
288 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
289 FILE *, fp, int, flag, char const *, format)
290 HOOK_FILE3(int, __vprintf_chk, stdout,
291 int, flag, char const *, format, va_list, ap)
292 HOOK_FILE4(int, __vfprintf_chk, stream,
293 FILE *, stream, int, flag, char const *, format, va_list, ap)
295 /* unlocked_stdio(3), only functions from above are hooked */
296 #ifdef HAVE_FWRITE_UNLOCKED
297 HOOK_FILE4(size_t, fwrite_unlocked, stream,
298 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
300 #ifdef HAVE_FPUTS_UNLOCKED
301 HOOK_FILE2(int, fputs_unlocked, stream,
302 char const *, s, FILE *, stream)
304 #ifdef HAVE_FPUTC_UNLOCKED
305 HOOK_FILE2(int, fputc_unlocked, stream,
306 int, c, FILE *, stream)
308 HOOK_FILE2(int, putc_unlocked, stream,
309 int, c, FILE *, stream)
310 HOOK_FILE1(int, putchar_unlocked, stdout,
312 /* glibc defines (_IO_)putc_unlocked() to a macro which either updates the
313 * output buffer or calls __overflow(). As this code is inlined we can't
314 * handle the first case, but if __overflow() is called we can color that
315 * part. As writes to stderr are never buffered, __overflow() is always called
316 * and everything works fine. This is only a problem if stdout is dupped to
317 * stderr (which shouldn't be the case too often). */
318 #if defined(HAVE_STRUCT__IO_FILE__FILENO) && defined(HAVE___OVERFLOW)
319 /* _IO_FILE is glibc's representation of FILE. */
320 HOOK_FILE2(int, __overflow, f, _IO_FILE *, f, int, ch)
322 /* Same for FreeBSD's libc. However it's more aggressive: The inline writing
323 * and __swbuf() are also used for normal output (e.g. putc()). Writing to
324 * stderr is still fine; it always calls __swbuf() as stderr is always
327 HOOK_FILE2(int, __swbuf, f, int, c, FILE *, f)
331 HOOK_VOID1(void, perror, STDERR_FILENO,
334 /* err(3), non standard BSD extension */
336 HOOK_VAR_VOID2(void, err, STDERR_FILENO, verr,
337 int, eval, char const *, fmt)
338 HOOK_VAR_VOID2(void, errx, STDERR_FILENO, verrx,
339 int, eval, char const *, fmt)
340 HOOK_VAR_VOID1(void, warn, STDERR_FILENO, vwarn,
342 HOOK_VAR_VOID1(void, warnx, STDERR_FILENO, vwarnx,
344 HOOK_FUNC_SIMPLE3(void, verr, int, eval, const char *, fmt, va_list, args) {
345 /* Can't use verr() directly as it terminates the process which prevents
346 * the post string from being printed. */
350 HOOK_FUNC_SIMPLE3(void, verrx, int, eval, const char *, fmt, va_list, args) {
355 HOOK_VOID2(void, vwarn, STDERR_FILENO,
356 char const *, fmt, va_list, args)
357 HOOK_VOID2(void, vwarnx, STDERR_FILENO,
358 char const *, fmt, va_list, args)
361 /* error(3), non-standard GNU extension */
363 static void error_vararg(int status, int errnum,
364 char const *filename, unsigned int linenum,
365 char const *format, va_list ap) {
366 static char const *last_filename;
367 static unsigned int last_linenum;
369 /* Skip this error message if requested and if there was already an error
370 * in the same file/line. */
371 if (error_one_per_line
372 && filename != NULL && linenum != 0
373 && filename == last_filename && linenum == last_linenum) {
376 last_filename = filename;
377 last_linenum = linenum;
379 error_message_count++;
383 if (error_print_progname) {
384 error_print_progname();
386 fprintf(stderr, "%s:", program_invocation_name);
388 if (filename != NULL && linenum != 0) {
389 fprintf(stderr, "%s:%u:", filename, linenum);
390 if (error_print_progname) {
391 fprintf(stderr, " ");
394 if (!error_print_progname) {
395 fprintf(stderr, " ");
399 vfprintf(stderr, format, ap);
402 fprintf(stderr, ": %s", strerror(errnum));
405 fprintf(stderr, "\n");
411 void error_at_line(int status, int errnum,
412 char const *filename, unsigned int linenum,
413 char const *format, ...) {
416 va_start(ap, format);
417 error_vararg(status, errnum, filename, linenum, format, ap);
420 void error(int status, int errnum, char const *format, ...) {
423 va_start(ap, format);
424 error_vararg(status, errnum, NULL, 0, format, ap);
430 /* Hook functions which duplicate file descriptors to track them. */
433 HOOK_FUNC_DEF1(int, dup, int, oldfd) {
436 DLSYM_FUNCTION(real_dup, "dup");
438 newfd = real_dup(oldfd);
440 dup_fd(oldfd, newfd);
445 /* int dup2(int, int) */
446 HOOK_FUNC_DEF2(int, dup2, int, oldfd, int, newfd) {
447 DLSYM_FUNCTION(real_dup2, "dup2");
449 newfd = real_dup2(oldfd, newfd);
451 dup_fd(oldfd, newfd);
456 /* int dup3(int, int, int) */
457 HOOK_FUNC_DEF3(int, dup3, int, oldfd, int, newfd, int, flags) {
458 DLSYM_FUNCTION(real_dup3, "dup3");
460 newfd = real_dup3(oldfd, newfd, flags);
462 dup_fd(oldfd, newfd);
468 /* int fcntl(int, int, ...) */
469 HOOK_FUNC_VAR_DEF2(int, fcntl, int, fd, int, cmd /*, ... */) {
473 DLSYM_FUNCTION(real_fcntl, "fcntl");
475 /* fcntl() takes different types of arguments depending on the cmd type
476 * (int, void and pointers are used at the moment). Handling these
477 * arguments for different systems and with possible changes in the future
480 * Therefore always retrieve a void-pointer from our arguments (even if it
481 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
482 * problems because a void-pointer is most-likely bigger than an int
483 * (something which is not true in reverse) and shouldn't cause
484 * truncation. For register based calling conventions an invalid register
485 * content is passed, but ignored by real_fcntl(). Not perfect, but should
489 result = real_fcntl(fd, cmd, va_arg(ap, void *));
492 /* We only care about duping fds. */
493 if (cmd == F_DUPFD && result > -1) {
501 HOOK_FUNC_DEF1(int, close, int, fd) {
502 DLSYM_FUNCTION(real_close, "close");
507 return real_close(fd);
509 /* int fclose(FILE *) */
510 HOOK_FUNC_DEF1(int, fclose, FILE *, fp) {
513 DLSYM_FUNCTION(real_fclose, "fclose");
515 if (fp != NULL && (fd = fileno(fp)) >= 0) {
518 return real_fclose(fp);
522 /* Hook functions which are necessary for correct tracking. */
524 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
526 /* vfork() is similar to fork() but the address space is shared between
527 * father and child. It's designed for fork()/exec() usage because it's
528 * faster than fork(). However according to the POSIX standard the "child"
529 * isn't allowed to perform any memory-modifications before the exec()
530 * (except the pid_t result variable of vfork()).
532 * As some programs don't adhere to the standard (e.g. the "child" closes
533 * or dups a descriptor before the exec()) and this breaks our tracking of
534 * file descriptors (e.g. it gets closed in the parent as well), we just
535 * fork() instead. This is in compliance with the POSIX standard and as
536 * most systems use copy-on-write anyway not a performance issue. */
542 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
543 * a custom environment which doesn't necessarily contain our updates to
544 * ENV_NAME_PRIVATE_FDS. It's also faster to update the environment only when
545 * necessary, right before the exec(), to pass it to the new program. */
547 /* int execve(char const *, char * const [], char * const []) */
548 HOOK_FUNC_DEF3(int, execve, char const *, filename, char * const *, argv, char * const *, env) {
549 DLSYM_FUNCTION(real_execve, "execve");
551 /* Count environment variables. */
553 char * const *x = env;
557 /* Terminating NULL. */
560 char *env_copy[count + 1 /* space for our new entry if necessary */];
562 /* Make sure the information from the environment is loaded. We can't just
563 * do nothing (like update_environment()) because the caller might pass a
564 * different environment which doesn't include any of our settings. */
566 init_from_environment();
569 char fds_env[strlen(ENV_NAME_PRIVATE_FDS)
570 + 1 + update_environment_buffer_size()];
571 strcpy(fds_env, ENV_NAME_PRIVATE_FDS "=");
572 update_environment_buffer(fds_env + strlen(ENV_NAME_PRIVATE_FDS) + 1);
575 char **x_copy = env_copy;
577 /* Copy the environment manually; allows skipping elements. */
579 while ((*x_copy = *x)) {
580 /* Remove ENV_NAME_FDS if we've already used its value. The new
581 * program must use the updated list from ENV_NAME_PRIVATE_FDS. */
582 if (used_fds_set_by_user
583 && !strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
586 /* Update ENV_NAME_PRIVATE_FDS. */
587 } else if (!strncmp(*x, ENV_NAME_PRIVATE_FDS "=",
588 strlen(ENV_NAME_PRIVATE_FDS) + 1)) {
596 /* The loop "condition" NULL-terminates env_copy. */
599 /* If the process removed ENV_NAME_PRIVATE_FDS from the environment,
605 return real_execve(filename, argv, env_copy);
608 #define EXECL_COPY_VARARGS_START(args) \
612 /* Count arguments. */ \
613 size_t count = 1; /* arg */ \
615 while (va_arg(ap, char *)) { \
620 /* Copy varargs. */ \
621 char *args[count + 1 /* terminating NULL */]; \
622 args[0] = (char *)arg; /* there's no other way around the cast */ \
626 while ((x = va_arg(ap, char *))) { \
630 #define EXECL_COPY_VARARGS_END(args) \
632 #define EXECL_COPY_VARARGS(args) \
633 EXECL_COPY_VARARGS_START(args); \
634 EXECL_COPY_VARARGS_END(args);
636 int execl(char const *path, char const *arg, ...) {
637 EXECL_COPY_VARARGS(args);
639 /* execv() updates the environment. */
640 return execv(path, args);
642 int execlp(char const *file, char const *arg, ...) {
643 EXECL_COPY_VARARGS(args);
645 /* execvp() updates the environment. */
646 return execvp(file, args);
648 int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
651 EXECL_COPY_VARARGS_START(args);
652 /* Get envp[] located after arguments. */
653 envp = va_arg(ap, char * const *);
654 EXECL_COPY_VARARGS_END(args);
656 /* execve() updates the environment. */
657 return execve(path, args, envp);
660 /* int execv(char const *, char * const []) */
661 HOOK_FUNC_DEF2(int, execv, char const *, path, char * const *, argv) {
662 DLSYM_FUNCTION(real_execv, "execv");
664 update_environment();
665 return real_execv(path, argv);
668 /* int execvp(char const *, char * const []) */
669 HOOK_FUNC_DEF2(int, execvp, char const *, file, char * const *, argv) {
670 DLSYM_FUNCTION(real_execvp, "execvp");
672 update_environment();
673 return real_execvp(file, argv);
677 extern char **environ;
678 int execvpe(char const *file, char * const argv[], char * const envp[]) {
680 char **old_environ = environ;
682 /* Fake the environment so we can reuse execvp(). */
683 environ = (char **)envp;
685 /* execvp() updates the environment. */
686 result = execvp(file, argv);
688 environ = old_environ;