/* * Hook output functions (like printf(3)) with LD_PRELOAD to color stderr (or * other file descriptors). * * Copyright (C) 2013 Simon Ruderich * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see . */ #include "config.h" /* Must be loaded before the following headers. */ #include "ldpreload.h" #include #include #include #include #include #include /* Conflicting declaration in glibc. */ #undef fwrite_unlocked /* Used by various functions, including debug(). */ static ssize_t (*real_write)(int, const void *, size_t); static int (*real_close)(int); static size_t (*real_fwrite)(const void *, size_t, size_t, FILE *); /* Did we already (try to) parse the environment and setup the necessary * variables? */ static int initialized; /* Force hooked writes even when not writing to a tty. Used for tests. */ static int force_write_to_non_tty; #include "constants.h" #ifdef DEBUG # include "debug.h" #endif #include "hookmacros.h" #include "trackfds.h" /* Should the "action" handler be invoked for this file descriptor? */ static int check_handle_fd(int fd) { /* Load state from environment. Only necessary once per process. */ if (!initialized) { init_from_environment(); } /* Never touch anything not going to a terminal - unless we are explicitly * asked to do so. */ if (!force_write_to_non_tty && !isatty(fd)) { return 0; } if (tracked_fds_count == 0) { return 0; } return tracked_fds_find(fd); } static void dup_fd(int oldfd, int newfd) { #ifdef DEBUG debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid()); #endif if (!initialized) { init_from_environment(); } if (tracked_fds_count == 0) { return; } /* We are already tracking this file descriptor, add newfd to the list as * it will reference the same descriptor. */ if (tracked_fds_find(oldfd)) { if (!tracked_fds_find(newfd)) { tracked_fds_add(newfd); update_environment(); } /* We are not tracking this file descriptor, remove newfd from the list * (if present). */ } else { if (tracked_fds_remove(newfd)) { update_environment(); } } } static void close_fd(int fd) { #ifdef DEBUG debug("%3d -> .\t\t\t[%d]\n", fd, getpid()); #endif if (!initialized) { init_from_environment(); } if (tracked_fds_count == 0) { return; } tracked_fds_remove(fd); } /* "Action" handlers called when a file descriptor is matched. */ static char *pre_string; static size_t pre_string_size; static char *post_string; static size_t post_string_size; /* Load alternative pre/post strings from the environment if available, fall * back to default values. */ inline static void init_pre_post_string() { pre_string = getenv(ENV_NAME_PRE_STRING); if (!pre_string) { pre_string = DEFAULT_PRE_STRING; } pre_string_size = strlen(pre_string); post_string = getenv(ENV_NAME_POST_STRING); if (!post_string) { post_string = DEFAULT_POST_STRING; } post_string_size = strlen(post_string); } static void handle_fd_pre(int fd, int action) { (void)action; if (!pre_string || !post_string) { init_pre_post_string(); } DLSYM_FUNCTION(real_write, "write"); real_write(fd, pre_string, pre_string_size); } static void handle_fd_post(int fd, int action) { (void)action; /* write() already loaded above in handle_fd_pre(). */ real_write(fd, post_string, post_string_size); } static void handle_file_pre(FILE *stream, int action) { (void)action; if (!pre_string || !post_string) { init_pre_post_string(); } DLSYM_FUNCTION(real_fwrite, "fwrite"); real_fwrite(pre_string, pre_string_size, 1, stream); } static void handle_file_post(FILE *stream, int action) { (void)action; /* fwrite() already loaded above in handle_file_pre(). */ real_fwrite(post_string, post_string_size, 1, stream); } /* Hook all important output functions to manipulate their output. */ HOOK_FD3(ssize_t, write, fd, int, fd, const void *, buf, size_t, count) HOOK_FILE4(size_t, fwrite, stream, const void *, ptr, size_t, size, size_t, nmemb, FILE *, stream) /* puts(3) */ HOOK_FILE2(int, fputs, stream, const char *, s, FILE *, stream) HOOK_FILE2(int, fputc, stream, int, c, FILE *, stream) HOOK_FILE2(int, putc, stream, int, c, FILE *, stream) HOOK_FILE1(int, putchar, stdout, int, c) HOOK_FILE1(int, puts, stdout, const char *, s) /* printf(3), excluding all s*() and vs*() functions (no output) */ HOOK_VAR_FILE1(int, printf, stdout, vprintf, const char *, format) HOOK_VAR_FILE2(int, fprintf, stream, vfprintf, FILE *, stream, const char *, format) HOOK_FILE2(int, vprintf, stdout, const char *, format, va_list, ap) HOOK_FILE3(int, vfprintf, stream, FILE *, stream, const char *, format, va_list, ap) /* Hardening functions (-D_FORTIFY_SOURCE=2). */ HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk, int, flag, const char *, format) HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk, FILE *, fp, int, flag, const char *, format) HOOK_FILE3(int, __vprintf_chk, stdout, int, flag, const char *, format, va_list, ap) HOOK_FILE4(int, __vfprintf_chk, stream, FILE *, stream, int, flag, const char *, format, va_list, ap) /* unlocked_stdio(3), only functions from above are hooked */ HOOK_FILE4(size_t, fwrite_unlocked, stream, const void *, ptr, size_t, size, size_t, nmemb, FILE *, stream) HOOK_FILE2(int, fputs_unlocked, stream, const char *, s, FILE *, stream) HOOK_FILE2(int, fputc_unlocked, stream, int, c, FILE *, stream) HOOK_FILE2(int, putc_unlocked, stream, int, c, FILE *, stream) HOOK_FILE1(int, putchar_unlocked, stdout, int, c) HOOK_FILE1(int, puts_unlocked, stdout, const char *, s) /* perror(3) */ HOOK_VOID1(void, perror, STDERR_FILENO, const char *, s) /* Hook functions which duplicate file descriptors to track them. */ static int (*real_dup)(int); static int (*real_dup2)(int, int); static int (*real_dup3)(int, int, int); int dup(int oldfd) { int newfd; DLSYM_FUNCTION(real_dup, "dup"); newfd = real_dup(oldfd); if (newfd != -1) { int saved_errno = errno; dup_fd(oldfd, newfd); errno = saved_errno; } return newfd; } int dup2(int oldfd, int newfd) { DLSYM_FUNCTION(real_dup2, "dup2"); newfd = real_dup2(oldfd, newfd); if (newfd != -1) { int saved_errno = errno; dup_fd(oldfd, newfd); errno = saved_errno; } return newfd; } int dup3(int oldfd, int newfd, int flags) { DLSYM_FUNCTION(real_dup3, "dup3"); newfd = real_dup3(oldfd, newfd, flags); if (newfd != -1) { int saved_errno = errno; dup_fd(oldfd, newfd); errno = saved_errno; } return newfd; } static int (*real_fcntl)(int, int, ...); int fcntl(int fd, int cmd, ...) { int result; va_list ap; DLSYM_FUNCTION(real_fcntl, "fcntl"); /* fcntl() takes different types of arguments depending on the cmd type * (int, void and pointers are used at the moment). Handling these * arguments for different systems and with possible changes in the future * is error prone. * * Therefore always retrieve a void-pointer from our arguments (even if it * wasn't there) and pass it to real_fcntl(). This shouldn't cause any * problems because a void-pointer is most-likely bigger than an int * (something which is not true in reverse) and shouldn't cause * truncation. For register based calling conventions an invalid register * content is passed, but ignored by real_fcntl(). Not perfect, but should * work fine. */ va_start(ap, cmd); result = real_fcntl(fd, cmd, va_arg(ap, void *)); va_end(ap); /* We only care about duping fds. */ if (cmd == F_DUPFD && result != -1) { int saved_errno = errno; dup_fd(fd, result); errno = saved_errno; } return result; } static int (*real_close)(int); int close(int fd) { DLSYM_FUNCTION(real_close, "close"); close_fd(fd); return real_close(fd); } static int (*real_fclose)(FILE *); int fclose(FILE *fp) { DLSYM_FUNCTION(real_fclose, "fclose"); close_fd(fileno(fp)); return real_fclose(fp); } /* Hook functions which are necessary for correct tracking. */ #if defined(HAVE_VFORK) && defined(HAVE_FORK) pid_t vfork(void) { /* vfork() is similar to fork() but the address space is shared between * father and child. It's designed for fork()/exec() usage because it's * faster than fork(). However according to the POSIX standard the "child" * isn't allowed to perform any memory-modifications before the exec() * (except the pid_t result variable of vfork()). * * As some programs don't adhere to the standard (e.g. the "child" closes * or dups a descriptor before the exec()) and this breaks our tracking of * file descriptors (e.g. it gets closed in the parent as well), we just * fork() instead. This is in compliance with the POSIX standard and as * most systems use copy-on-write anyway not a performance issue. */ return fork(); } #endif