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      1 /*
      2  * Copyright (C) 2012-2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #include <ctype.h>
     18 #include <limits.h>
     19 #include <stdio.h>
     20 #include <sys/cdefs.h>
     21 #include <sys/prctl.h>
     22 #include <sys/socket.h>
     23 #include <sys/types.h>
     24 #include <sys/un.h>
     25 #include <unistd.h>
     26 
     27 #include <cutils/sockets.h>
     28 #include <private/android_filesystem_config.h>
     29 #include <private/android_logger.h>
     30 
     31 #include "LogBuffer.h"
     32 #include "LogListener.h"
     33 #include "LogUtils.h"
     34 
     35 LogListener::LogListener(LogBufferInterface* buf, LogReader* reader)
     36     : SocketListener(getLogSocket(), false), logbuf(buf), reader(reader) {
     37 }
     38 
     39 bool LogListener::onDataAvailable(SocketClient* cli) {
     40     static bool name_set;
     41     if (!name_set) {
     42         prctl(PR_SET_NAME, "logd.writer");
     43         name_set = true;
     44     }
     45 
     46     char buffer[sizeof_log_id_t + sizeof(uint16_t) + sizeof(log_time) +
     47                 LOGGER_ENTRY_MAX_PAYLOAD];
     48     struct iovec iov = { buffer, sizeof(buffer) };
     49 
     50     alignas(4) char control[CMSG_SPACE(sizeof(struct ucred))];
     51     struct msghdr hdr = {
     52         NULL, 0, &iov, 1, control, sizeof(control), 0,
     53     };
     54 
     55     int socket = cli->getSocket();
     56 
     57     // To clear the entire buffer is secure/safe, but this contributes to 1.68%
     58     // overhead under logging load. We are safe because we check counts.
     59     // memset(buffer, 0, sizeof(buffer));
     60     ssize_t n = recvmsg(socket, &hdr, 0);
     61     if (n <= (ssize_t)(sizeof(android_log_header_t))) {
     62         return false;
     63     }
     64 
     65     struct ucred* cred = NULL;
     66 
     67     struct cmsghdr* cmsg = CMSG_FIRSTHDR(&hdr);
     68     while (cmsg != NULL) {
     69         if (cmsg->cmsg_level == SOL_SOCKET &&
     70             cmsg->cmsg_type == SCM_CREDENTIALS) {
     71             cred = (struct ucred*)CMSG_DATA(cmsg);
     72             break;
     73         }
     74         cmsg = CMSG_NXTHDR(&hdr, cmsg);
     75     }
     76 
     77     struct ucred fake_cred;
     78     if (cred == NULL) {
     79         cred = &fake_cred;
     80         cred->pid = 0;
     81         cred->uid = DEFAULT_OVERFLOWUID;
     82     }
     83 
     84     if (cred->uid == AID_LOGD) {
     85         // ignore log messages we send to ourself.
     86         // Such log messages are often generated by libraries we depend on
     87         // which use standard Android logging.
     88         return false;
     89     }
     90 
     91     android_log_header_t* header =
     92         reinterpret_cast<android_log_header_t*>(buffer);
     93     if (/* header->id < LOG_ID_MIN || */ header->id >= LOG_ID_MAX ||
     94         header->id == LOG_ID_KERNEL) {
     95         return false;
     96     }
     97 
     98     if ((header->id == LOG_ID_SECURITY) &&
     99         (!__android_log_security() ||
    100          !clientHasLogCredentials(cred->uid, cred->gid, cred->pid))) {
    101         return false;
    102     }
    103 
    104     // Check credential validity, acquire corrected details if not supplied.
    105     if (cred->pid == 0) {
    106         cred->pid = logbuf ? logbuf->tidToPid(header->tid)
    107                            : android::tidToPid(header->tid);
    108         if (cred->pid == getpid()) {
    109             // We expect that /proc/<tid>/ is accessible to self even without
    110             // readproc group, so that we will always drop messages that come
    111             // from any of our logd threads and their library calls.
    112             return false;  // ignore self
    113         }
    114     }
    115     if (cred->uid == DEFAULT_OVERFLOWUID) {
    116         uid_t uid =
    117             logbuf ? logbuf->pidToUid(cred->pid) : android::pidToUid(cred->pid);
    118         if (uid == AID_LOGD) {
    119             uid = logbuf ? logbuf->pidToUid(header->tid)
    120                          : android::pidToUid(cred->pid);
    121         }
    122         if (uid != AID_LOGD) cred->uid = uid;
    123     }
    124 
    125     char* msg = ((char*)buffer) + sizeof(android_log_header_t);
    126     n -= sizeof(android_log_header_t);
    127 
    128     // NB: hdr.msg_flags & MSG_TRUNC is not tested, silently passing a
    129     // truncated message to the logs.
    130 
    131     if (logbuf != nullptr) {
    132         int res = logbuf->log(
    133             (log_id_t)header->id, header->realtime, cred->uid, cred->pid,
    134             header->tid, msg,
    135             ((size_t)n <= USHRT_MAX) ? (unsigned short)n : USHRT_MAX);
    136         if (res > 0 && reader != nullptr) {
    137             reader->notifyNewLog();
    138         }
    139     }
    140 
    141     return true;
    142 }
    143 
    144 int LogListener::getLogSocket() {
    145     static const char socketName[] = "logdw";
    146     int sock = android_get_control_socket(socketName);
    147 
    148     if (sock < 0) {  // logd started up in init.sh
    149         sock = socket_local_server(
    150             socketName, ANDROID_SOCKET_NAMESPACE_RESERVED, SOCK_DGRAM);
    151 
    152         int on = 1;
    153         if (setsockopt(sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on))) {
    154             return -1;
    155         }
    156     }
    157     return sock;
    158 }
    159