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/*
* Copyright (c) 2019 Yubico AB. All rights reserved.
* Use of this source code is governed by a BSD-style
* license that can be found in the LICENSE file.
* SPDX-License-Identifier: BSD-2-Clause
*/
/*
* cc -fPIC -D_GNU_SOURCE -shared -o preload-snoop.so preload-snoop.c
* LD_PRELOAD=$(realpath preload-snoop.so)
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <dlfcn.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define SNOOP_DEV_PREFIX "/dev/hidraw"
struct fd_tuple {
int snoop_in;
int snoop_out;
int real_dev;
};
static struct fd_tuple *fd_tuple;
static int (*open_f)(const char *, int, mode_t);
static int (*close_f)(int);
static ssize_t (*read_f)(int, void *, size_t);
static ssize_t (*write_f)(int, const void *, size_t);
static int
get_fd(const char *hid_path, const char *suffix)
{
char *s = NULL;
char path[PATH_MAX];
int fd;
int r;
if ((s = strdup(hid_path)) == NULL) {
warnx("%s: strdup", __func__);
return (-1);
}
for (size_t i = 0; i < strlen(s); i++)
if (s[i] == '/')
s[i] = '_';
if ((r = snprintf(path, sizeof(path), "%s-%s", s, suffix)) < 0 ||
(size_t)r >= sizeof(path)) {
warnx("%s: snprintf", __func__);
free(s);
return (-1);
}
free(s);
s = NULL;
if ((fd = open_f(path, O_CREAT | O_WRONLY, 0644)) < 0) {
warn("%s: open", __func__);
return (-1);
}
return (fd);
}
int
open(const char *path, int flags, ...)
{
va_list ap;
mode_t mode;
va_start(ap, flags);
mode = va_arg(ap, mode_t);
va_end(ap);
if (open_f == NULL) {
open_f = dlsym(RTLD_NEXT, "open");
if (open_f == NULL) {
warnx("%s: dlsym", __func__);
errno = EACCES;
return (-1);
}
}
if (strncmp(path, SNOOP_DEV_PREFIX, strlen(SNOOP_DEV_PREFIX)) != 0)
return (open_f(path, flags, mode));
if (fd_tuple != NULL) {
warnx("%s: fd_tuple != NULL", __func__);
errno = EACCES;
return (-1);
}
if ((fd_tuple = calloc(1, sizeof(*fd_tuple))) == NULL) {
warn("%s: calloc", __func__);
errno = ENOMEM;
return (-1);
}
fd_tuple->snoop_in = -1;
fd_tuple->snoop_out = -1;
fd_tuple->real_dev = -1;
if ((fd_tuple->snoop_in = get_fd(path, "in")) < 0 ||
(fd_tuple->snoop_out = get_fd(path, "out")) < 0 ||
(fd_tuple->real_dev = open_f(path, flags, mode)) < 0) {
warn("%s: get_fd/open", __func__);
goto fail;
}
return (fd_tuple->real_dev);
fail:
if (fd_tuple->snoop_in != -1)
close(fd_tuple->snoop_in);
if (fd_tuple->snoop_out != -1)
close(fd_tuple->snoop_out);
if (fd_tuple->real_dev != -1)
close(fd_tuple->real_dev);
free(fd_tuple);
fd_tuple = NULL;
errno = EACCES;
return (-1);
}
int
close(int fd)
{
if (close_f == NULL) {
close_f = dlsym(RTLD_NEXT, "close");
if (close_f == NULL) {
warnx("%s: dlsym", __func__);
errno = EBADF;
return (-1);
}
}
if (fd_tuple == NULL || fd_tuple->real_dev != fd)
return (close_f(fd));
close_f(fd_tuple->snoop_in);
close_f(fd_tuple->snoop_out);
close_f(fd_tuple->real_dev);
free(fd_tuple);
fd_tuple = NULL;
return (0);
}
ssize_t
read(int fd, void *buf, size_t nbytes)
{
ssize_t n;
if (read_f == NULL) {
read_f = dlsym(RTLD_NEXT, "read");
if (read_f == NULL) {
warnx("%s: dlsym", __func__);
errno = EBADF;
return (-1);
}
}
if (write_f == NULL) {
write_f = dlsym(RTLD_NEXT, "write");
if (write_f == NULL) {
warnx("%s: dlsym", __func__);
errno = EBADF;
return (-1);
}
}
if (fd_tuple == NULL || fd_tuple->real_dev != fd)
return (read_f(fd, buf, nbytes));
if ((n = read_f(fd, buf, nbytes)) < 0 ||
write_f(fd_tuple->snoop_in, buf, n) != n)
return (-1);
return (n);
}
ssize_t
write(int fd, const void *buf, size_t nbytes)
{
ssize_t n;
if (write_f == NULL) {
write_f = dlsym(RTLD_NEXT, "write");
if (write_f == NULL) {
warnx("%s: dlsym", __func__);
errno = EBADF;
return (-1);
}
}
if (fd_tuple == NULL || fd_tuple->real_dev != fd)
return (write_f(fd, buf, nbytes));
if ((n = write_f(fd, buf, nbytes)) < 0 ||
write_f(fd_tuple->snoop_out, buf, n) != n)
return (-1);
return (n);
}
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