1 /* 2 * Copyright 2012, Samsung Telecommunications of America 3 * Copyright (C) 2014 The Android Open Source Project 4 * 5 * Licensed under the Apache License, Version 2.0 (the "License"); 6 * you may not use this file except in compliance with the License. 7 * You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 * 17 * Written by William Roberts <w.roberts (at) sta.samsung.com> 18 * 19 */ 20 21 #include <errno.h> 22 #include <string.h> 23 #include <unistd.h> 24 25 #define LOG_TAG "libaudit" 26 #include <log/log.h> 27 28 #include "libaudit.h" 29 30 /** 31 * Waits for an ack from the kernel 32 * @param fd 33 * The netlink socket fd 34 * @param seq 35 * The current sequence number were acking on 36 * @return 37 * This function returns 0 on success, else -errno. 38 */ 39 static int get_ack(int fd, int16_t seq) 40 { 41 int rc; 42 struct audit_message rep; 43 44 /* Sanity check, this is an internal interface this shouldn't happen */ 45 if (fd < 0) { 46 return -EINVAL; 47 } 48 49 rc = audit_get_reply(fd, &rep, GET_REPLY_BLOCKING, MSG_PEEK); 50 if (rc < 0) { 51 return rc; 52 } 53 54 if (rep.nlh.nlmsg_type == NLMSG_ERROR) { 55 audit_get_reply(fd, &rep, GET_REPLY_BLOCKING, 0); 56 rc = ((struct nlmsgerr *)rep.data)->error; 57 if (rc) { 58 return -rc; 59 } 60 } 61 62 if ((int16_t)rep.nlh.nlmsg_seq != seq) { 63 SLOGW("Expected sequence number between user space and kernel space is out of skew, " 64 "expected %u got %u", seq, rep.nlh.nlmsg_seq); 65 } 66 67 return 0; 68 } 69 70 /** 71 * 72 * @param fd 73 * The netlink socket fd 74 * @param type 75 * The type of netlink message 76 * @param data 77 * The data to send 78 * @param size 79 * The length of the data in bytes 80 * @return 81 * This function returns a positive sequence number on success, else -errno. 82 */ 83 static int audit_send(int fd, int type, const void *data, size_t size) 84 { 85 int rc; 86 static int16_t sequence = 0; 87 struct audit_message req; 88 struct sockaddr_nl addr; 89 90 memset(&req, 0, sizeof(req)); 91 memset(&addr, 0, sizeof(addr)); 92 93 /* We always send netlink messaged */ 94 addr.nl_family = AF_NETLINK; 95 96 /* Set up the netlink headers */ 97 req.nlh.nlmsg_type = type; 98 req.nlh.nlmsg_len = NLMSG_SPACE(size); 99 req.nlh.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK; 100 101 /* 102 * Check for a valid fd, even though sendto would catch this, its easier 103 * to always blindly increment the sequence number 104 */ 105 if (fd < 0) { 106 return -EBADF; 107 } 108 109 /* Ensure the message is not too big */ 110 if (NLMSG_SPACE(size) > MAX_AUDIT_MESSAGE_LENGTH) { 111 SLOGE("netlink message is too large"); 112 return -EINVAL; 113 } 114 115 /* Only memcpy in the data if it was specified */ 116 if (size && data) { 117 memcpy(NLMSG_DATA(&req.nlh), data, size); 118 } 119 120 /* 121 * Only increment the sequence number on a guarantee 122 * you will send it to the kernel. 123 * 124 * Also, the sequence is defined as a u32 in the kernel 125 * struct. Using an int here might not work on 32/64 bit splits. A 126 * signed 64 bit value can overflow a u32..but a u32 127 * might not fit in the response, so we need to use s32. 128 * Which is still kind of hackish since int could be 16 bits 129 * in size. The only safe type to use here is a signed 16 130 * bit value. 131 */ 132 req.nlh.nlmsg_seq = ++sequence; 133 134 /* While failing and its due to interrupts */ 135 136 rc = TEMP_FAILURE_RETRY(sendto(fd, &req, req.nlh.nlmsg_len, 0, 137 (struct sockaddr*) &addr, sizeof(addr))); 138 139 /* Not all the bytes were sent */ 140 if (rc < 0) { 141 rc = -errno; 142 SLOGE("Error sending data over the netlink socket: %s", strerror(-errno)); 143 goto out; 144 } else if ((uint32_t) rc != req.nlh.nlmsg_len) { 145 rc = -EPROTO; 146 goto out; 147 } 148 149 /* We sent all the bytes, get the ack */ 150 rc = get_ack(fd, sequence); 151 152 /* If the ack failed, return the error, else return the sequence number */ 153 rc = (rc == 0) ? (int) sequence : rc; 154 155 out: 156 /* Don't let sequence roll to negative */ 157 if (sequence < 0) { 158 SLOGW("Auditd to Kernel sequence number has rolled over"); 159 sequence = 0; 160 } 161 162 return rc; 163 } 164 165 int audit_setup(int fd, uint32_t pid) 166 { 167 int rc; 168 struct audit_message rep; 169 struct audit_status status; 170 171 memset(&status, 0, sizeof(status)); 172 173 /* 174 * In order to set the auditd PID we send an audit message over the netlink 175 * socket with the pid field of the status struct set to our current pid, 176 * and the the mask set to AUDIT_STATUS_PID 177 */ 178 status.pid = pid; 179 status.mask = AUDIT_STATUS_PID | AUDIT_STATUS_RATE_LIMIT; 180 status.rate_limit = 20; // audit entries per second 181 182 /* Let the kernel know this pid will be registering for audit events */ 183 rc = audit_send(fd, AUDIT_SET, &status, sizeof(status)); 184 if (rc < 0) { 185 SLOGE("Could net set pid for audit events, error: %s", strerror(-rc)); 186 return rc; 187 } 188 189 /* 190 * In a request where we need to wait for a response, wait for the message 191 * and discard it. This message confirms and sync's us with the kernel. 192 * This daemon is now registered as the audit logger. 193 * 194 * TODO 195 * If the daemon dies and restarts the message didn't come back, 196 * so I went to non-blocking and it seemed to fix the bug. 197 * Need to investigate further. 198 */ 199 audit_get_reply(fd, &rep, GET_REPLY_NONBLOCKING, 0); 200 201 return 0; 202 } 203 204 int audit_open() 205 { 206 return socket(PF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_AUDIT); 207 } 208 209 int audit_get_reply(int fd, struct audit_message *rep, reply_t block, int peek) 210 { 211 ssize_t len; 212 int flags; 213 int rc = 0; 214 215 struct sockaddr_nl nladdr; 216 socklen_t nladdrlen = sizeof(nladdr); 217 218 if (fd < 0) { 219 return -EBADF; 220 } 221 222 /* Set up the flags for recv from */ 223 flags = (block == GET_REPLY_NONBLOCKING) ? MSG_DONTWAIT : 0; 224 flags |= peek; 225 226 /* 227 * Get the data from the netlink socket but on error we need to be carefull, 228 * the interface shows that EINTR can never be returned, other errors, 229 * however, can be returned. 230 */ 231 len = TEMP_FAILURE_RETRY(recvfrom(fd, rep, sizeof(*rep), flags, 232 (struct sockaddr*) &nladdr, &nladdrlen)); 233 234 /* 235 * EAGAIN should be re-tried until success or another error manifests. 236 */ 237 if (len < 0) { 238 rc = -errno; 239 if (block == GET_REPLY_NONBLOCKING && rc == -EAGAIN) { 240 /* If request is non blocking and errno is EAGAIN, just return 0 */ 241 return 0; 242 } 243 SLOGE("Error receiving from netlink socket, error: %s", strerror(-rc)); 244 return rc; 245 } 246 247 if (nladdrlen != sizeof(nladdr)) { 248 SLOGE("Protocol fault, error: %s", strerror(EPROTO)); 249 return -EPROTO; 250 } 251 252 /* Make sure the netlink message was not spoof'd */ 253 if (nladdr.nl_pid) { 254 SLOGE("Invalid netlink pid received, expected 0 got: %d", nladdr.nl_pid); 255 return -EINVAL; 256 } 257 258 /* Check if the reply from the kernel was ok */ 259 if (!NLMSG_OK(&rep->nlh, (size_t)len)) { 260 rc = (len == sizeof(*rep)) ? -EFBIG : -EBADE; 261 SLOGE("Bad kernel response %s", strerror(-rc)); 262 } 263 264 return rc; 265 } 266 267 void audit_close(int fd) 268 { 269 int rc = close(fd); 270 if (rc < 0) { 271 SLOGE("Attempting to close invalid fd %d, error: %s", fd, strerror(errno)); 272 } 273 return; 274 } 275
