2 * Hook output functions (like printf(3)) with LD_PRELOAD to color stderr (or
3 * other file descriptors).
5 * Copyright (C) 2013-2018 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. */
52 #ifdef HAVE_STRUCT__IO_FILE__FILENO
56 /* The following functions may be macros. Undefine them or they cause build
57 * failures when used in our hook macros below. */
59 /* In glibc, real fwrite_unlocked() is called in macro. */
60 #ifdef HAVE_FWRITE_UNLOCKED
61 # undef fwrite_unlocked
63 /* In Clang when compiling with hardening flags (fortify) on Debian Wheezy. */
66 /* On FreeBSD (9.1), __swbuf() is used instead of these macros. */
71 # undef putchar_unlocked
75 /* Used by various functions, including debug(). */
76 static ssize_t (*real_write)(int, void const *, size_t);
77 static int (*real_close)(int);
78 static size_t (*real_fwrite)(void const *, size_t, size_t, FILE *);
80 /* Did we already (try to) parse the environment and setup the necessary
82 static int initialized;
83 /* Force hooked writes even when not writing to a tty. Used for tests. */
84 static int force_write_to_non_tty;
85 /* Was ENV_NAME_FDS found and used when init_from_environment() was called?
86 * This is not true if the process set it manually after initialization. */
87 static int used_fds_set_by_user;
88 /* Was any of our handle_*_pre()/handle_*_post() functions called recursively?
89 * If so don't print the pre/post string for the recursive calls. This is
90 * necessary on some systems (e.g. FreeBSD 9.1) which call multiple hooked
91 * functions while printing a string (e.g. a FILE * and a fd hook function is
92 * called). This is not thread-safe if TLS is not available. */
93 static TLS int handle_recursive;
96 #include "constants.h"
101 #include "hookmacros.h"
102 #include "trackfds.h"
106 /* See hookmacros.h for the decision if a function call is colored. */
109 /* Prevent inlining into hook functions because it may increase the number of
110 * spilled registers unnecessarily. As it's not called very often accept the
111 * additional call. */
112 static int isatty_noinline(int fd) noinline;
113 static int isatty_noinline(int fd) {
116 int saved_errno = errno;
117 int result = isatty(fd);
124 static void dup_fd(int oldfd, int newfd) {
126 debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
129 assert(oldfd >= 0 && newfd >= 0);
131 if (unlikely(!initialized)) {
132 init_from_environment();
135 /* We are already tracking this file descriptor, add newfd to the list as
136 * it will reference the same descriptor. */
137 if (tracked_fds_find(oldfd)) {
138 if (!tracked_fds_find(newfd)) {
139 tracked_fds_add(newfd);
141 /* We are not tracking this file descriptor, remove newfd from the list
144 tracked_fds_remove(newfd);
148 static void close_fd(int fd) {
150 debug("%3d -> .\t\t\t[%d]\n", fd, getpid());
155 if (unlikely(!initialized)) {
156 init_from_environment();
159 tracked_fds_remove(fd);
163 /* "Action" handlers called when a file descriptor is matched. */
165 static char const *pre_string;
166 static size_t pre_string_size;
167 static char const *post_string;
168 static size_t post_string_size;
170 /* Load alternative pre/post strings from the environment if available, fall
171 * back to default values. */
172 static void init_pre_post_string(void) {
173 pre_string = getenv(ENV_NAME_PRE_STRING);
175 pre_string = DEFAULT_PRE_STRING;
177 pre_string_size = strlen(pre_string);
179 post_string = getenv(ENV_NAME_POST_STRING);
181 post_string = DEFAULT_POST_STRING;
183 post_string_size = strlen(post_string);
186 /* Don't inline any of the pre/post functions. Keep the hook function as small
187 * as possible for speed reasons. */
188 static void handle_fd_pre(int fd) noinline;
189 static void handle_fd_post(int fd) noinline;
190 static void handle_file_pre(FILE *stream) noinline;
191 static void handle_file_post(FILE *stream) noinline;
193 static void handle_fd_pre(int fd) {
194 if (handle_recursive++ > 0) {
198 int saved_errno = errno;
200 if (unlikely(!pre_string)) {
201 init_pre_post_string();
204 DLSYM_FUNCTION(real_write, "write");
205 real_write(fd, pre_string, pre_string_size);
209 static void handle_fd_post(int fd) {
210 if (--handle_recursive > 0) {
214 int saved_errno = errno;
216 /* write() already loaded above in handle_fd_pre(). */
217 real_write(fd, post_string, post_string_size);
222 static void handle_file_pre(FILE *stream) {
223 if (handle_recursive++ > 0) {
227 int saved_errno = errno;
229 if (unlikely(!pre_string)) {
230 init_pre_post_string();
233 DLSYM_FUNCTION(real_fwrite, "fwrite");
234 real_fwrite(pre_string, pre_string_size, 1, stream);
238 static void handle_file_post(FILE *stream) {
239 if (--handle_recursive > 0) {
243 int saved_errno = errno;
245 /* fwrite() already loaded above in handle_file_pre(). */
246 real_fwrite(post_string, post_string_size, 1, stream);
253 /* Hook all important output functions to manipulate their output. */
255 HOOK_FD3(ssize_t, write, fd,
256 int, fd, void const *, buf, size_t, count)
257 HOOK_FILE4(size_t, fwrite, stream,
258 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
261 HOOK_FILE2(int, fputs, stream,
262 char const *, s, FILE *, stream)
263 HOOK_FILE2(int, fputc, stream,
264 int, c, FILE *, stream)
265 HOOK_FILE2(int, putc, stream,
266 int, c, FILE *, stream)
267 /* The glibc uses a macro for putc() which expands to _IO_putc(). However
268 * sometimes the raw putc() is used as well, not sure why. Make sure to hook
272 HOOK_FILE2(int, putc, stream,
273 int, c, FILE *, stream)
275 HOOK_FILE1(int, putchar, stdout,
277 HOOK_FILE1(int, puts, stdout,
280 /* printf(3), excluding all s*() and vs*() functions (no output) */
281 HOOK_VAR_FILE1(int, printf, stdout, vprintf,
282 char const *, format)
283 HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
284 FILE *, stream, char const *, format)
285 HOOK_FILE2(int, vprintf, stdout,
286 char const *, format, va_list, ap)
287 HOOK_FILE3(int, vfprintf, stream,
288 FILE *, stream, char const *, format, va_list, ap)
289 /* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
290 HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
291 int, flag, char const *, format)
292 HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
293 FILE *, fp, int, flag, char const *, format)
294 HOOK_FILE3(int, __vprintf_chk, stdout,
295 int, flag, char const *, format, va_list, ap)
296 HOOK_FILE4(int, __vfprintf_chk, stream,
297 FILE *, stream, int, flag, char const *, format, va_list, ap)
299 /* unlocked_stdio(3), only functions from above are hooked */
300 #ifdef HAVE_FWRITE_UNLOCKED
301 HOOK_FILE4(size_t, fwrite_unlocked, stream,
302 void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
304 #ifdef HAVE_FPUTS_UNLOCKED
305 HOOK_FILE2(int, fputs_unlocked, stream,
306 char const *, s, FILE *, stream)
308 #ifdef HAVE_FPUTC_UNLOCKED
309 HOOK_FILE2(int, fputc_unlocked, stream,
310 int, c, FILE *, stream)
312 HOOK_FILE2(int, putc_unlocked, stream,
313 int, c, FILE *, stream)
314 HOOK_FILE1(int, putchar_unlocked, stdout,
316 /* glibc defines (_IO_)putc_unlocked() to a macro which either updates the
317 * output buffer or calls __overflow(). As this code is inlined we can't
318 * handle the first case, but if __overflow() is called we can color that
319 * part. As writes to stderr are never buffered, __overflow() is always called
320 * and everything works fine. This is only a problem if stdout is dupped to
321 * stderr (which shouldn't be the case too often). */
322 #if defined(HAVE_STRUCT__IO_FILE__FILENO) && defined(HAVE___OVERFLOW)
323 /* _IO_FILE is glibc's representation of FILE. */
324 HOOK_FILE2(int, __overflow, f, _IO_FILE *, f, int, ch)
326 /* Same for FreeBSD's libc. However it's more aggressive: The inline writing
327 * and __swbuf() are also used for normal output (e.g. putc()). Writing to
328 * stderr is still fine; it always calls __swbuf() as stderr is always
331 HOOK_FILE2(int, __swbuf, f, int, c, FILE *, f)
335 HOOK_VOID1(void, perror, STDERR_FILENO,
338 /* err(3), non standard BSD extension */
340 HOOK_VAR_VOID2(void, err, STDERR_FILENO, verr,
341 int, eval, char const *, fmt)
342 HOOK_VAR_VOID2(void, errx, STDERR_FILENO, verrx,
343 int, eval, char const *, fmt)
344 HOOK_VAR_VOID1(void, warn, STDERR_FILENO, vwarn,
346 HOOK_VAR_VOID1(void, warnx, STDERR_FILENO, vwarnx,
348 HOOK_FUNC_SIMPLE3(void, verr, int, eval, const char *, fmt, va_list, args) {
349 /* Can't use verr() directly as it terminates the process which prevents
350 * the post string from being printed. */
354 HOOK_FUNC_SIMPLE3(void, verrx, int, eval, const char *, fmt, va_list, args) {
359 HOOK_VOID2(void, vwarn, STDERR_FILENO,
360 char const *, fmt, va_list, args)
361 HOOK_VOID2(void, vwarnx, STDERR_FILENO,
362 char const *, fmt, va_list, args)
365 /* error(3), non-standard GNU extension */
367 static void error_vararg(int status, int errnum,
368 char const *filename, unsigned int linenum,
369 char const *format, va_list ap) {
370 static char const *last_filename;
371 static unsigned int last_linenum;
373 /* Skip this error message if requested and if there was already an error
374 * in the same file/line. */
375 if (error_one_per_line
376 && filename != NULL && linenum != 0
377 && filename == last_filename && linenum == last_linenum) {
380 last_filename = filename;
381 last_linenum = linenum;
383 error_message_count++;
387 if (error_print_progname) {
388 error_print_progname();
390 fprintf(stderr, "%s:", program_invocation_name);
392 if (filename != NULL && linenum != 0) {
393 fprintf(stderr, "%s:%u:", filename, linenum);
394 if (error_print_progname) {
395 fprintf(stderr, " ");
398 if (!error_print_progname) {
399 fprintf(stderr, " ");
403 vfprintf(stderr, format, ap);
406 fprintf(stderr, ": %s", strerror(errnum));
409 fprintf(stderr, "\n");
416 void error_at_line(int status, int errnum,
417 char const *filename, unsigned int linenum,
418 char const *format, ...) {
421 va_start(ap, format);
422 error_vararg(status, errnum, filename, linenum, format, ap);
425 void error(int status, int errnum, char const *format, ...) {
428 va_start(ap, format);
429 error_vararg(status, errnum, NULL, 0, format, ap);
435 /* Hook functions which duplicate file descriptors to track them. */
438 HOOK_FUNC_DEF1(int, dup, int, oldfd) {
441 DLSYM_FUNCTION(real_dup, "dup");
443 newfd = real_dup(oldfd);
445 dup_fd(oldfd, newfd);
450 /* int dup2(int, int) */
451 HOOK_FUNC_DEF2(int, dup2, int, oldfd, int, newfd) {
452 DLSYM_FUNCTION(real_dup2, "dup2");
454 newfd = real_dup2(oldfd, newfd);
456 dup_fd(oldfd, newfd);
461 /* int dup3(int, int, int) */
462 HOOK_FUNC_DEF3(int, dup3, int, oldfd, int, newfd, int, flags) {
463 DLSYM_FUNCTION(real_dup3, "dup3");
465 newfd = real_dup3(oldfd, newfd, flags);
467 dup_fd(oldfd, newfd);
473 /* int fcntl(int, int, ...) */
474 HOOK_FUNC_VAR_DEF2(int, fcntl, int, fd, int, cmd /*, ... */) {
478 DLSYM_FUNCTION(real_fcntl, "fcntl");
480 /* fcntl() takes different types of arguments depending on the cmd type
481 * (int, void and pointers are used at the moment). Handling these
482 * arguments for different systems and with possible changes in the future
485 * Therefore always retrieve a void-pointer from our arguments (even if it
486 * wasn't there) and pass it to real_fcntl(). This shouldn't cause any
487 * problems because a void-pointer is most-likely bigger than an int
488 * (something which is not true in reverse) and shouldn't cause
489 * truncation. For register based calling conventions an invalid register
490 * content is passed, but ignored by real_fcntl(). Not perfect, but should
494 result = real_fcntl(fd, cmd, va_arg(ap, void *));
497 /* We only care about duping fds. */
498 if (cmd == F_DUPFD && result > -1) {
506 HOOK_FUNC_DEF1(int, close, int, fd) {
507 DLSYM_FUNCTION(real_close, "close");
512 return real_close(fd);
514 /* int fclose(FILE *) */
515 HOOK_FUNC_DEF1(int, fclose, FILE *, fp) {
518 DLSYM_FUNCTION(real_fclose, "fclose");
520 if (fp != NULL && (fd = fileno(fp)) >= 0) {
523 return real_fclose(fp);
527 /* Hook functions which are necessary for correct tracking. */
529 #if defined(HAVE_VFORK) && defined(HAVE_FORK)
531 /* vfork() is similar to fork() but the address space is shared between
532 * father and child. It's designed for fork()/exec() usage because it's
533 * faster than fork(). However according to the POSIX standard the "child"
534 * isn't allowed to perform any memory-modifications before the exec()
535 * (except the pid_t result variable of vfork()).
537 * As we have to store changes to the file descriptors in memory (e.g. the
538 * "child" closes or dups a descriptor before the exec()) and this
539 * modifies the parent as well due to the semantics of vfork() - thus
540 * breaking the requirements of vfork(), we just use fork instead(). This
541 * is in compliance with the POSIX standard and as most systems use
542 * copy-on-write anyway not a performance issue. */
548 /* Hook execve() and the other exec*() functions. Some shells use exec*() with
549 * a custom environment which doesn't necessarily contain our updates to
550 * ENV_NAME_PRIVATE_FDS. It's also faster to update the environment only when
551 * necessary, right before the exec(), to pass it to the new program. */
553 /* int execve(char const *, char * const [], char * const []) */
554 HOOK_FUNC_DEF3(int, execve, char const *, filename, char * const *, argv, char * const *, env) {
555 DLSYM_FUNCTION(real_execve, "execve");
557 char * const fake_env[] = {NULL};
562 /* Count environment variables. */
564 char * const *x = env;
568 /* Terminating NULL. */
571 char *env_copy[count + 1 /* space for our new entry if necessary */];
573 /* Make sure the information from the environment is loaded. We can't just
574 * do nothing (like update_environment()) because the caller might pass a
575 * different environment which doesn't include any of our settings. */
577 init_from_environment();
580 char fds_env[strlen(ENV_NAME_PRIVATE_FDS)
581 + 1 + update_environment_buffer_size()];
582 strcpy(fds_env, ENV_NAME_PRIVATE_FDS "=");
583 update_environment_buffer(fds_env + strlen(ENV_NAME_PRIVATE_FDS) + 1);
586 char **x_copy = env_copy;
588 /* Copy the environment manually; allows skipping elements. */
590 while ((*x_copy = *x)) {
591 /* Remove ENV_NAME_FDS if we've already used its value. The new
592 * program must use the updated list from ENV_NAME_PRIVATE_FDS. */
593 if (used_fds_set_by_user
594 && !strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
597 /* Update ENV_NAME_PRIVATE_FDS. */
598 } else if (!strncmp(*x, ENV_NAME_PRIVATE_FDS "=",
599 strlen(ENV_NAME_PRIVATE_FDS) + 1)) {
607 /* The loop "condition" NULL-terminates env_copy. */
610 /* If the process removed ENV_NAME_PRIVATE_FDS from the environment,
616 return real_execve(filename, argv, env_copy);
619 #define EXECL_COPY_VARARGS_START(args) \
623 /* Count arguments. */ \
624 size_t count = 1; /* arg */ \
626 while (va_arg(ap, char *)) { \
631 /* Copy varargs. */ \
632 char *args[count + 1 /* terminating NULL */]; \
633 args[0] = (char *)arg; /* there's no other way around the cast */ \
637 while ((x = va_arg(ap, char *))) { \
641 #define EXECL_COPY_VARARGS_END(args) \
643 #define EXECL_COPY_VARARGS(args) \
644 EXECL_COPY_VARARGS_START(args); \
645 EXECL_COPY_VARARGS_END(args);
647 int execl(char const *path, char const *arg, ...) {
648 EXECL_COPY_VARARGS(args);
650 /* execv() updates the environment. */
651 return execv(path, args);
653 int execlp(char const *file, char const *arg, ...) {
654 EXECL_COPY_VARARGS(args);
656 /* execvp() updates the environment. */
657 return execvp(file, args);
659 int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
662 EXECL_COPY_VARARGS_START(args);
663 /* Get envp[] located after arguments. */
664 envp = va_arg(ap, char * const *);
665 EXECL_COPY_VARARGS_END(args);
667 /* execve() updates the environment. */
668 return execve(path, args, envp);
671 /* int execv(char const *, char * const []) */
672 HOOK_FUNC_DEF2(int, execv, char const *, path, char * const *, argv) {
673 DLSYM_FUNCTION(real_execv, "execv");
675 update_environment();
676 return real_execv(path, argv);
679 /* int execvp(char const *, char * const []) */
680 HOOK_FUNC_DEF2(int, execvp, char const *, file, char * const *, argv) {
681 DLSYM_FUNCTION(real_execvp, "execvp");
683 update_environment();
684 return real_execvp(file, argv);
688 extern char **environ;
689 int execvpe(char const *file, char * const argv[], char * const envp[]) {
691 char **old_environ = environ;
693 /* Fake the environment so we can reuse execvp(). */
694 environ = (char **)envp;
696 /* execvp() updates the environment. */
697 result = execvp(file, argv);
699 environ = old_environ;