/*
* Hook output functions (like printf(3)) with LD_PRELOAD to color stderr (or
* other file descriptors).
*
* Copyright (C) 2013-2014 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
#include "compiler.h"
/* Must be loaded before the following headers. */
#include "ldpreload.h"
/* Disable assert()s if not compiled with --enable-debug. */
#ifndef DEBUG
# define NDEBUG
#endif
#ifndef TLS
# define TLS
#endif
#include
#include
#include
#include
#include
#include
#include
#include
#ifdef HAVE_ERR_H
# include
#endif
#ifdef HAVE_ERROR_H
# include
#endif
#ifdef HAVE_STRUCT__IO_FILE__FILENO
# include
#endif
/* The following functions may be macros. Undefine them or they cause build
* failures when used in our hook macros below. */
/* In glibc, real fwrite_unlocked() is called in macro. */
#ifdef HAVE_FWRITE_UNLOCKED
# undef fwrite_unlocked
#endif
/* In Clang when compiling with hardening flags (fortify) on Debian Wheezy. */
#undef printf
#undef fprintf
/* On FreeBSD (9.1), __swbuf() is used instead of these macros. */
#ifdef HAVE___SWBUF
# undef putc
# undef putc_unlocked
# undef putchar
# undef putchar_unlocked
#endif
/* Used by various functions, including debug(). */
static ssize_t (*real_write)(int, void const *, size_t);
static int (*real_close)(int);
static size_t (*real_fwrite)(void const *, 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;
/* Was ENV_NAME_FDS found and used when init_from_environment() was called?
* This is not true if the process set it manually after initialization. */
static int used_fds_set_by_user;
/* Was any of our handle_*_pre()/handle_*_post() functions called recursively?
* If so don't print the pre/post string for the recursive calls. This is
* necessary on some systems (e.g. FreeBSD 9.1) which call multiple hooked
* functions while printing a string (e.g. a FILE * and a fd hook function is
* called). This is not thread-safe if TLS is not available. */
static TLS int handle_recursive;
#include "constants.h"
#ifdef WARNING
# include "debug.h"
#endif
#include "hookmacros.h"
#include "trackfds.h"
/* See hookmacros.h for the decision if a function call is colored. */
/* Prevent inlining into hook functions because it may increase the number of
* spilled registers unnecessarily. As it's not called very often accept the
* additional call. */
static int isatty_noinline(int fd) noinline;
static int isatty_noinline(int fd) {
assert(fd >= 0);
int saved_errno = errno;
int result = isatty(fd);
errno = saved_errno;
return result;
}
static void dup_fd(int oldfd, int newfd) {
#ifdef DEBUG
debug("%3d -> %3d\t\t\t[%d]\n", oldfd, newfd, getpid());
#endif
assert(oldfd >= 0 && newfd >= 0);
if (unlikely(!initialized)) {
init_from_environment();
}
/* 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);
}
/* We are not tracking this file descriptor, remove newfd from the list
* (if present). */
} else {
tracked_fds_remove(newfd);
}
}
static void close_fd(int fd) {
#ifdef DEBUG
debug("%3d -> .\t\t\t[%d]\n", fd, getpid());
#endif
assert(fd >= 0);
if (unlikely(!initialized)) {
init_from_environment();
}
tracked_fds_remove(fd);
}
/* "Action" handlers called when a file descriptor is matched. */
static char const *pre_string;
static size_t pre_string_size;
static char const *post_string;
static size_t post_string_size;
/* Load alternative pre/post strings from the environment if available, fall
* back to default values. */
static void init_pre_post_string(void) {
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);
}
/* Don't inline any of the pre/post functions. Keep the hook function as small
* as possible for speed reasons. */
static void handle_fd_pre(int fd) noinline;
static void handle_fd_post(int fd) noinline;
static void handle_file_pre(FILE *stream) noinline;
static void handle_file_post(FILE *stream) noinline;
static void handle_fd_pre(int fd) {
if (handle_recursive++ > 0) {
return;
}
int saved_errno = errno;
if (unlikely(!pre_string)) {
init_pre_post_string();
}
DLSYM_FUNCTION(real_write, "write");
real_write(fd, pre_string, pre_string_size);
errno = saved_errno;
}
static void handle_fd_post(int fd) {
if (--handle_recursive > 0) {
return;
}
int saved_errno = errno;
/* write() already loaded above in handle_fd_pre(). */
real_write(fd, post_string, post_string_size);
errno = saved_errno;
}
static void handle_file_pre(FILE *stream) {
if (handle_recursive++ > 0) {
return;
}
int saved_errno = errno;
if (unlikely(!pre_string)) {
init_pre_post_string();
}
DLSYM_FUNCTION(real_fwrite, "fwrite");
real_fwrite(pre_string, pre_string_size, 1, stream);
errno = saved_errno;
}
static void handle_file_post(FILE *stream) {
if (--handle_recursive > 0) {
return;
}
int saved_errno = errno;
/* fwrite() already loaded above in handle_file_pre(). */
real_fwrite(post_string, post_string_size, 1, stream);
errno = saved_errno;
}
/* Hook all important output functions to manipulate their output. */
HOOK_FD3(ssize_t, write, fd,
int, fd, void const *, buf, size_t, count)
HOOK_FILE4(size_t, fwrite, stream,
void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
/* puts(3) */
HOOK_FILE2(int, fputs, stream,
char const *, s, FILE *, stream)
HOOK_FILE2(int, fputc, stream,
int, c, FILE *, stream)
HOOK_FILE2(int, putc, stream,
int, c, FILE *, stream)
/* The glibc uses a macro for putc() which expands to _IO_putc(). However
* sometimes the raw putc() is used as well, not sure why. Make sure to hook
* it too. */
#ifdef putc
# undef putc
HOOK_FILE2(int, putc, stream,
int, c, FILE *, stream)
#endif
HOOK_FILE1(int, putchar, stdout,
int, c)
HOOK_FILE1(int, puts, stdout,
char const *, s)
/* printf(3), excluding all s*() and vs*() functions (no output) */
HOOK_VAR_FILE1(int, printf, stdout, vprintf,
char const *, format)
HOOK_VAR_FILE2(int, fprintf, stream, vfprintf,
FILE *, stream, char const *, format)
HOOK_FILE2(int, vprintf, stdout,
char const *, format, va_list, ap)
HOOK_FILE3(int, vfprintf, stream,
FILE *, stream, char const *, format, va_list, ap)
/* Hardening functions (-D_FORTIFY_SOURCE=2), only functions from above */
HOOK_VAR_FILE2(int, __printf_chk, stdout, __vprintf_chk,
int, flag, char const *, format)
HOOK_VAR_FILE3(int, __fprintf_chk, fp, __vfprintf_chk,
FILE *, fp, int, flag, char const *, format)
HOOK_FILE3(int, __vprintf_chk, stdout,
int, flag, char const *, format, va_list, ap)
HOOK_FILE4(int, __vfprintf_chk, stream,
FILE *, stream, int, flag, char const *, format, va_list, ap)
/* unlocked_stdio(3), only functions from above are hooked */
#ifdef HAVE_FWRITE_UNLOCKED
HOOK_FILE4(size_t, fwrite_unlocked, stream,
void const *, ptr, size_t, size, size_t, nmemb, FILE *, stream)
#endif
#ifdef HAVE_FPUTS_UNLOCKED
HOOK_FILE2(int, fputs_unlocked, stream,
char const *, s, FILE *, stream)
#endif
#ifdef HAVE_FPUTC_UNLOCKED
HOOK_FILE2(int, fputc_unlocked, stream,
int, c, FILE *, stream)
#endif
HOOK_FILE2(int, putc_unlocked, stream,
int, c, FILE *, stream)
HOOK_FILE1(int, putchar_unlocked, stdout,
int, c)
/* glibc defines (_IO_)putc_unlocked() to a macro which either updates the
* output buffer or calls __overflow(). As this code is inlined we can't
* handle the first case, but if __overflow() is called we can color that
* part. As writes to stderr are never buffered, __overflow() is always called
* and everything works fine. This is only a problem if stdout is dupped to
* stderr (which shouldn't be the case too often). */
#if defined(HAVE_STRUCT__IO_FILE__FILENO) && defined(HAVE___OVERFLOW)
/* _IO_FILE is glibc's representation of FILE. */
HOOK_FILE2(int, __overflow, f, _IO_FILE *, f, int, ch)
#endif
/* Same for FreeBSD's libc. However it's more aggressive: The inline writing
* and __swbuf() are also used for normal output (e.g. putc()). Writing to
* stderr is still fine; it always calls __swbuf() as stderr is always
* unbuffered. */
#ifdef HAVE___SWBUF
HOOK_FILE2(int, __swbuf, f, int, c, FILE *, f)
#endif
/* perror(3) */
HOOK_VOID1(void, perror, STDERR_FILENO,
char const *, s)
/* err(3), non standard BSD extension */
#ifdef HAVE_ERR_H
HOOK_VAR_VOID2(void, err, STDERR_FILENO, verr,
int, eval, char const *, fmt)
HOOK_VAR_VOID2(void, errx, STDERR_FILENO, verrx,
int, eval, char const *, fmt)
HOOK_VAR_VOID1(void, warn, STDERR_FILENO, vwarn,
char const *, fmt)
HOOK_VAR_VOID1(void, warnx, STDERR_FILENO, vwarnx,
char const *, fmt)
HOOK_FUNC_SIMPLE3(void, verr, int, eval, const char *, fmt, va_list, args) {
/* Can't use verr() directly as it terminates the process which prevents
* the post string from being printed. */
vwarn(fmt, args);
exit(eval);
}
HOOK_FUNC_SIMPLE3(void, verrx, int, eval, const char *, fmt, va_list, args) {
/* See verr(). */
vwarnx(fmt, args);
exit(eval);
}
HOOK_VOID2(void, vwarn, STDERR_FILENO,
char const *, fmt, va_list, args)
HOOK_VOID2(void, vwarnx, STDERR_FILENO,
char const *, fmt, va_list, args)
#endif
/* error(3), non-standard GNU extension */
#ifdef HAVE_ERROR_H
static void error_vararg(int status, int errnum,
char const *filename, unsigned int linenum,
char const *format, va_list ap) {
static char const *last_filename;
static unsigned int last_linenum;
/* Skip this error message if requested and if there was already an error
* in the same file/line. */
if (error_one_per_line
&& filename != NULL && linenum != 0
&& filename == last_filename && linenum == last_linenum) {
goto out;
}
last_filename = filename;
last_linenum = linenum;
error_message_count++;
fflush(stdout);
if (error_print_progname) {
error_print_progname();
} else {
fprintf(stderr, "%s:", program_invocation_name);
}
if (filename != NULL && linenum != 0) {
fprintf(stderr, "%s:%u:", filename, linenum);
if (error_print_progname) {
fprintf(stderr, " ");
}
}
if (!error_print_progname) {
fprintf(stderr, " ");
}
vfprintf(stderr, format, ap);
if (errnum != 0) {
fprintf(stderr, ": %s", strerror(errnum));
}
fprintf(stderr, "\n");
out:
if (status != 0) {
exit(status);
}
}
void error_at_line(int status, int errnum,
char const *filename, unsigned int linenum,
char const *format, ...) {
va_list ap;
va_start(ap, format);
error_vararg(status, errnum, filename, linenum, format, ap);
va_end(ap);
}
void error(int status, int errnum, char const *format, ...) {
va_list ap;
va_start(ap, format);
error_vararg(status, errnum, NULL, 0, format, ap);
va_end(ap);
}
#endif
/* Hook functions which duplicate file descriptors to track them. */
/* int dup(int) */
HOOK_FUNC_DEF1(int, dup, int, oldfd) {
int newfd;
DLSYM_FUNCTION(real_dup, "dup");
newfd = real_dup(oldfd);
if (newfd > -1) {
dup_fd(oldfd, newfd);
}
return newfd;
}
/* int dup2(int, int) */
HOOK_FUNC_DEF2(int, dup2, int, oldfd, int, newfd) {
DLSYM_FUNCTION(real_dup2, "dup2");
newfd = real_dup2(oldfd, newfd);
if (newfd > -1) {
dup_fd(oldfd, newfd);
}
return newfd;
}
/* int dup3(int, int, int) */
HOOK_FUNC_DEF3(int, dup3, int, oldfd, int, newfd, int, flags) {
DLSYM_FUNCTION(real_dup3, "dup3");
newfd = real_dup3(oldfd, newfd, flags);
if (newfd > -1) {
dup_fd(oldfd, newfd);
}
return newfd;
}
/* int fcntl(int, int, ...) */
HOOK_FUNC_VAR_DEF2(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) {
dup_fd(fd, result);
}
return result;
}
/* int close(int) */
HOOK_FUNC_DEF1(int, close, int, fd) {
DLSYM_FUNCTION(real_close, "close");
if (fd >= 0) {
close_fd(fd);
}
return real_close(fd);
}
/* int fclose(FILE *) */
HOOK_FUNC_DEF1(int, fclose, FILE *, fp) {
int fd;
DLSYM_FUNCTION(real_fclose, "fclose");
if (fp != NULL && (fd = fileno(fp)) >= 0) {
close_fd(fd);
}
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
/* Hook execve() and the other exec*() functions. Some shells use exec*() with
* a custom environment which doesn't necessarily contain our updates to
* ENV_NAME_PRIVATE_FDS. It's also faster to update the environment only when
* necessary, right before the exec(), to pass it to the new program. */
/* int execve(char const *, char * const [], char * const []) */
HOOK_FUNC_DEF3(int, execve, char const *, filename, char * const *, argv, char * const *, env) {
DLSYM_FUNCTION(real_execve, "execve");
/* Count environment variables. */
size_t count = 0;
char * const *x = env;
while (*x++) {
count++;
}
/* Terminating NULL. */
count++;
char *env_copy[count + 1 /* space for our new entry if necessary */];
/* Make sure the information from the environment is loaded. We can't just
* do nothing (like update_environment()) because the caller might pass a
* different environment which doesn't include any of our settings. */
if (!initialized) {
init_from_environment();
}
char fds_env[strlen(ENV_NAME_PRIVATE_FDS)
+ 1 + update_environment_buffer_size()];
strcpy(fds_env, ENV_NAME_PRIVATE_FDS "=");
update_environment_buffer(fds_env + strlen(ENV_NAME_PRIVATE_FDS) + 1);
int found = 0;
char **x_copy = env_copy;
/* Copy the environment manually; allows skipping elements. */
x = env;
while ((*x_copy = *x)) {
/* Remove ENV_NAME_FDS if we've already used its value. The new
* program must use the updated list from ENV_NAME_PRIVATE_FDS. */
if (used_fds_set_by_user
&& !strncmp(*x, ENV_NAME_FDS "=", strlen(ENV_NAME_FDS) + 1)) {
x++;
continue;
/* Update ENV_NAME_PRIVATE_FDS. */
} else if (!strncmp(*x, ENV_NAME_PRIVATE_FDS "=",
strlen(ENV_NAME_PRIVATE_FDS) + 1)) {
*x_copy = fds_env;
found = 1;
}
x++;
x_copy++;
}
/* The loop "condition" NULL-terminates env_copy. */
if (!found) {
/* If the process removed ENV_NAME_PRIVATE_FDS from the environment,
* re-add it. */
*x_copy++ = fds_env;
*x_copy++ = NULL;
}
return real_execve(filename, argv, env_copy);
}
#define EXECL_COPY_VARARGS_START(args) \
va_list ap; \
char *x; \
\
/* Count arguments. */ \
size_t count = 1; /* arg */ \
va_start(ap, arg); \
while (va_arg(ap, char *)) { \
count++; \
} \
va_end(ap); \
\
/* Copy varargs. */ \
char *args[count + 1 /* terminating NULL */]; \
args[0] = (char *)arg; /* there's no other way around the cast */ \
\
size_t i = 1; \
va_start(ap, arg); \
while ((x = va_arg(ap, char *))) { \
args[i++] = x; \
} \
args[i] = NULL;
#define EXECL_COPY_VARARGS_END(args) \
va_end(ap);
#define EXECL_COPY_VARARGS(args) \
EXECL_COPY_VARARGS_START(args); \
EXECL_COPY_VARARGS_END(args);
int execl(char const *path, char const *arg, ...) {
EXECL_COPY_VARARGS(args);
/* execv() updates the environment. */
return execv(path, args);
}
int execlp(char const *file, char const *arg, ...) {
EXECL_COPY_VARARGS(args);
/* execvp() updates the environment. */
return execvp(file, args);
}
int execle(char const *path, char const *arg, ... /*, char * const envp[] */) {
char * const *envp;
EXECL_COPY_VARARGS_START(args);
/* Get envp[] located after arguments. */
envp = va_arg(ap, char * const *);
EXECL_COPY_VARARGS_END(args);
/* execve() updates the environment. */
return execve(path, args, envp);
}
/* int execv(char const *, char * const []) */
HOOK_FUNC_DEF2(int, execv, char const *, path, char * const *, argv) {
DLSYM_FUNCTION(real_execv, "execv");
update_environment();
return real_execv(path, argv);
}
/* int execvp(char const *, char * const []) */
HOOK_FUNC_DEF2(int, execvp, char const *, file, char * const *, argv) {
DLSYM_FUNCTION(real_execvp, "execvp");
update_environment();
return real_execvp(file, argv);
}
#ifdef HAVE_EXECVPE
extern char **environ;
int execvpe(char const *file, char * const argv[], char * const envp[]) {
int result;
char **old_environ = environ;
/* Fake the environment so we can reuse execvp(). */
environ = (char **)envp;
/* execvp() updates the environment. */
result = execvp(file, argv);
environ = old_environ;
return result;
}
#endif