am 6bc08280: Validate sender credentials on netlink msg receive

#include <sys/types.h>

#include <sys/socket.h>

#include <linux/netlink.h>

#include <string.h>

#define LOG_TAG "NetlinkListener"

bool NetlinkListener::onDataAvailable(SocketClient *cli)

{

    int socket = cli->getSocket();

    int count;

    ssize_t count;

    char cred_msg[CMSG_SPACE(sizeof(struct ucred))];

    struct sockaddr_nl snl;

    struct iovec iov = {mBuffer, sizeof(mBuffer)};

    struct msghdr hdr = {&snl, sizeof(snl), &iov, 1, cred_msg, sizeof(cred_msg), 0};

    count = TEMP_FAILURE_RETRY(recv(socket, mBuffer, sizeof(mBuffer), 0));

    count = TEMP_FAILURE_RETRY(recvmsg(socket, &hdr, 0));

    if (count < 0) {

        SLOGE("recv failed (%s)", strerror(errno));

        SLOGE("recvmsg failed (%s)", strerror(errno));

        return false;

    }

    if ((snl.nl_groups != 1) || (snl.nl_pid != 0)) {

        SLOGE("ignoring non-kernel netlink multicast message");

        return false;

    }

    struct cmsghdr * cmsg = CMSG_FIRSTHDR(&hdr);

    if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {

        SLOGE("ignoring message with no sender credentials");

        return false;

    }

    struct ucred * cred = (struct ucred *)CMSG_DATA(cmsg);

    if (cred->uid != 0) {

        SLOGE("ignoring message from non-root UID %d", cred->uid);

        return false;

    }