blob: ee34045b3f6e1b4941c3cab2ff2d7c6f5e9f11b6 [file] [log] [blame]
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "sandbox/linux/services/libc_urandom_override.h"
#include <dlfcn.h>
#include <pthread.h>
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include "base/eintr_wrapper.h"
#include "base/logging.h"
#include "base/rand_util.h"
// Note: this file is used by the zygote and nacl_helper.
namespace sandbox {
// With SELinux we can carve out a precise sandbox, so we don't have to play
// with intercepting libc calls.
#if !defined(CHROMIUM_SELINUX)
static bool g_override_urandom = false;
void InitLibcUrandomOverrides() {
// Make sure /dev/urandom is open.
base::GetUrandomFD();
g_override_urandom = true;
}
// TODO(sergeyu): Currently this code doesn't work properly under ASAN
// - it crashes content_unittests. Make sure it works properly and
// enable it here. http://crbug.com/123263
#if !defined(ADDRESS_SANITIZER)
static const char kUrandomDevPath[] = "/dev/urandom";
typedef FILE* (*FopenFunction)(const char* path, const char* mode);
typedef int (*XstatFunction)(int version, const char *path, struct stat *buf);
typedef int (*Xstat64Function)(int version, const char *path,
struct stat64 *buf);
static pthread_once_t g_libc_file_io_funcs_guard = PTHREAD_ONCE_INIT;
static FopenFunction g_libc_fopen;
static FopenFunction g_libc_fopen64;
static XstatFunction g_libc_xstat;
static Xstat64Function g_libc_xstat64;
static void InitLibcFileIOFunctions() {
g_libc_fopen = reinterpret_cast<FopenFunction>(
dlsym(RTLD_NEXT, "fopen"));
g_libc_fopen64 = reinterpret_cast<FopenFunction>(
dlsym(RTLD_NEXT, "fopen64"));
if (!g_libc_fopen) {
LOG(FATAL) << "Failed to get fopen() from libc.";
} else if (!g_libc_fopen64) {
#if !defined(OS_OPENBSD) && !defined(OS_FREEBSD)
LOG(WARNING) << "Failed to get fopen64() from libc. Using fopen() instead.";
#endif // !defined(OS_OPENBSD) && !defined(OS_FREEBSD)
g_libc_fopen64 = g_libc_fopen;
}
// TODO(sergeyu): This works only on systems with glibc. Fix it to
// work properly on other systems if necessary.
g_libc_xstat = reinterpret_cast<XstatFunction>(
dlsym(RTLD_NEXT, "__xstat"));
g_libc_xstat64 = reinterpret_cast<Xstat64Function>(
dlsym(RTLD_NEXT, "__xstat64"));
if (!g_libc_xstat) {
LOG(FATAL) << "Failed to get __xstat() from libc.";
}
if (!g_libc_xstat64) {
LOG(WARNING) << "Failed to get __xstat64() from libc.";
}
}
// fopen() and fopen64() are intercepted here so that NSS can open
// /dev/urandom to seed its random number generator. NSS is used by
// remoting in the sendbox.
// fopen() call may be redirected to fopen64() in stdio.h using
// __REDIRECT(), which sets asm name for fopen() to "fopen64". This
// means that we cannot override fopen() directly here. Instead the
// the code below defines fopen_override() function with asm name
// "fopen", so that all references to fopen() will resolve to this
// function.
__attribute__ ((__visibility__("default")))
FILE* fopen_override(const char* path, const char* mode) __asm__ ("fopen");
__attribute__ ((__visibility__("default")))
FILE* fopen_override(const char* path, const char* mode) {
if (g_override_urandom && strcmp(path, kUrandomDevPath) == 0) {
int fd = HANDLE_EINTR(dup(base::GetUrandomFD()));
if (fd < 0) {
PLOG(ERROR) << "dup() failed.";
return NULL;
}
return fdopen(fd, mode);
} else {
CHECK_EQ(0, pthread_once(&g_libc_file_io_funcs_guard,
InitLibcFileIOFunctions));
return g_libc_fopen(path, mode);
}
}
__attribute__ ((__visibility__("default")))
FILE* fopen64(const char* path, const char* mode) {
if (g_override_urandom && strcmp(path, kUrandomDevPath) == 0) {
int fd = HANDLE_EINTR(dup(base::GetUrandomFD()));
if (fd < 0) {
PLOG(ERROR) << "dup() failed.";
return NULL;
}
return fdopen(fd, mode);
} else {
CHECK_EQ(0, pthread_once(&g_libc_file_io_funcs_guard,
InitLibcFileIOFunctions));
return g_libc_fopen64(path, mode);
}
}
// stat() is subject to the same problem as fopen(), so we have to use
// the same trick to override it.
__attribute__ ((__visibility__("default")))
int xstat_override(int version,
const char *path,
struct stat *buf) __asm__ ("__xstat");
__attribute__ ((__visibility__("default")))
int xstat_override(int version, const char *path, struct stat *buf) {
if (g_override_urandom && strcmp(path, kUrandomDevPath) == 0) {
int result = __fxstat(version, base::GetUrandomFD(), buf);
return result;
} else {
CHECK_EQ(0, pthread_once(&g_libc_file_io_funcs_guard,
InitLibcFileIOFunctions));
return g_libc_xstat(version, path, buf);
}
}
__attribute__ ((__visibility__("default")))
int xstat64_override(int version,
const char *path,
struct stat64 *buf) __asm__ ("__xstat64");
__attribute__ ((__visibility__("default")))
int xstat64_override(int version, const char *path, struct stat64 *buf) {
if (g_override_urandom && strcmp(path, kUrandomDevPath) == 0) {
int result = __fxstat64(version, base::GetUrandomFD(), buf);
return result;
} else {
CHECK_EQ(0, pthread_once(&g_libc_file_io_funcs_guard,
InitLibcFileIOFunctions));
CHECK(g_libc_xstat64);
return g_libc_xstat64(version, path, buf);
}
}
#endif // !ADDRESS_SANITIZER
#endif // !CHROMIUM_SELINUX
} // namespace content