libcutils: android_get_control_file uses realpath.

#include <sys/types.h>

#include <unistd.h>

#include <string>

#include <android-base/file.h>

#include <android-base/stringprintf.h>

#include "android_get_control_env.h"

int __android_get_control_from_env(const char* prefix, const char* name) {

}

int android_get_control_file(const char* path) {

    int fd = __android_get_control_from_env(ANDROID_FILE_ENV_PREFIX, path);

    std::string given_path;

    if (!android::base::Realpath(path, &given_path)) return -1;

    // Find file path from /proc and make sure it is correct

    char *proc = NULL;

    if (asprintf(&proc, "/proc/self/fd/%d", fd) < 0) return -1;

    if (!proc) return -1;

    size_t len = strlen(path);

    // readlink() does not guarantee a nul byte, len+2 so we catch truncation.

    char *buf = static_cast<char *>(calloc(1, len + 2));

    if (!buf) {

        free(proc);

        return -1;

    // Try path, then realpath(path), as keys to get the fd from env.

    auto fd = __android_get_control_from_env(ANDROID_FILE_ENV_PREFIX, path);

    if (fd < 0) {

        fd = __android_get_control_from_env(ANDROID_FILE_ENV_PREFIX, given_path.c_str());

        if (fd < 0) return fd;

    }

    ssize_t ret = TEMP_FAILURE_RETRY(readlink(proc, buf, len + 1));

    free(proc);

    int cmp = (len != static_cast<size_t>(ret)) || strcmp(buf, path);

    free(buf);

    if (ret < 0) return -1;

    if (cmp != 0) return -1;

    // Find file path from /proc and make sure it is correct

    auto proc = android::base::StringPrintf("/proc/self/fd/%d", fd);

    std::string fd_path;

    if (!android::base::Realpath(proc, &fd_path)) return -1;

    if (given_path != fd_path) return -1;

    // It is what we think it is

    return fd;