bool LogListener::onDataAvailable(SocketClient *cli) {
static bool name_set;
if (!name_set) {
prctl(PR_SET_NAME, "logd.writer");
name_set = true;
}
char buffer[sizeof_log_id_t + sizeof(uint16_t) + sizeof(log_time)
+ LOGGER_ENTRY_MAX_PAYLOAD];
struct iovec iov = { buffer, sizeof(buffer) };
char control[CMSG_SPACE(sizeof(struct ucred))] __aligned(4);
struct msghdr hdr = {
NULL,
0,
&iov,
1,
control,
sizeof(control),
0,
};
int socket = cli->getSocket();
// To clear the entire buffer is secure/safe, but this contributes to 1.68%
// overhead under logging load. We are safe because we check counts.
// memset(buffer, 0, sizeof(buffer));
ssize_t n = recvmsg(socket, &hdr, 0);
if (n <= (ssize_t)(sizeof(android_log_header_t))) {
return false;
}
struct ucred *cred = NULL;
struct cmsghdr *cmsg = CMSG_FIRSTHDR(&hdr);
while (cmsg != NULL) {
if (cmsg->cmsg_level == SOL_SOCKET
&& cmsg->cmsg_type == SCM_CREDENTIALS) {
cred = (struct ucred *)CMSG_DATA(cmsg);
break;
}
cmsg = CMSG_NXTHDR(&hdr, cmsg);
}
if (cred == NULL) {
return false;
}
if (cred->uid == AID_LOGD) {
// ignore log messages we send to ourself.
// Such log messages are often generated by libraries we depend on
// which use standard Android logging.
return false;
}
android_log_header_t *header = reinterpret_cast<android_log_header_t *>(buffer);
if (/* header->id < LOG_ID_MIN || */ header->id >= LOG_ID_MAX || header->id == LOG_ID_KERNEL) {
return false;
}
if ((header->id == LOG_ID_SECURITY) &&
(!__android_log_security() ||
!clientHasLogCredentials(cred->uid, cred->gid, cred->pid))) {
return false;
}
char *msg = ((char *)buffer) + sizeof(android_log_header_t);
n -= sizeof(android_log_header_t);
// NB: hdr.msg_flags & MSG_TRUNC is not tested, silently passing a
// truncated message to the logs.
if (logbuf->log((log_id_t)header->id, header->realtime,
cred->uid, cred->pid, header->tid, msg,
((size_t) n <= USHRT_MAX) ? (unsigned short) n : USHRT_MAX) >= 0) {
reader->notifyNewLog();
}
return true;
}
/*
* Measure the time it takes for __android_log_security.
*/
static void BM_security(benchmark::State& state) {
while (state.KeepRunning()) {
__android_log_security();
}
}