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@sta.samsung.com>
18 *
19 */
20
21 #include <errno.h>
22 #include <string.h>
23 #include <unistd.h>
24
25 #include "libaudit.h"
26
27 /**
28 * Waits for an ack from the kernel
29 * @param fd
30 * The netlink socket fd
31 * @return
32 * This function returns 0 on success, else -errno.
33 */
get_ack(int fd)34 static int get_ack(int fd) {
35 int rc;
36 struct audit_message rep;
37
38 /* Sanity check, this is an internal interface this shouldn't happen */
39 if (fd < 0) {
40 return -EINVAL;
41 }
42
43 rc = audit_get_reply(fd, &rep, GET_REPLY_BLOCKING, MSG_PEEK);
44 if (rc < 0) {
45 return rc;
46 }
47
48 if (rep.nlh.nlmsg_type == NLMSG_ERROR) {
49 audit_get_reply(fd, &rep, GET_REPLY_BLOCKING, 0);
50 rc = ((struct nlmsgerr*)rep.data)->error;
51 if (rc) {
52 return -rc;
53 }
54 }
55
56 return 0;
57 }
58
59 /**
60 *
61 * @param fd
62 * The netlink socket fd
63 * @param type
64 * The type of netlink message
65 * @param data
66 * The data to send
67 * @param size
68 * The length of the data in bytes
69 * @return
70 * This function returns a positive sequence number on success, else -errno.
71 */
audit_send(int fd,int type,const void * data,size_t size)72 static int audit_send(int fd, int type, const void* data, size_t size) {
73 int rc;
74 static int16_t sequence = 0;
75 struct audit_message req;
76 struct sockaddr_nl addr;
77
78 memset(&req, 0, sizeof(req));
79 memset(&addr, 0, sizeof(addr));
80
81 /* We always send netlink messaged */
82 addr.nl_family = AF_NETLINK;
83
84 /* Set up the netlink headers */
85 req.nlh.nlmsg_type = type;
86 req.nlh.nlmsg_len = NLMSG_SPACE(size);
87 req.nlh.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
88
89 /*
90 * Check for a valid fd, even though sendto would catch this, its easier
91 * to always blindly increment the sequence number
92 */
93 if (fd < 0) {
94 return -EBADF;
95 }
96
97 /* Ensure the message is not too big */
98 if (NLMSG_SPACE(size) > MAX_AUDIT_MESSAGE_LENGTH) {
99 return -EINVAL;
100 }
101
102 /* Only memcpy in the data if it was specified */
103 if (size && data) {
104 memcpy(NLMSG_DATA(&req.nlh), data, size);
105 }
106
107 /*
108 * Only increment the sequence number on a guarantee
109 * you will send it to the kernel.
110 *
111 * Also, the sequence is defined as a u32 in the kernel
112 * struct. Using an int here might not work on 32/64 bit splits. A
113 * signed 64 bit value can overflow a u32..but a u32
114 * might not fit in the response, so we need to use s32.
115 * Which is still kind of hackish since int could be 16 bits
116 * in size. The only safe type to use here is a signed 16
117 * bit value.
118 */
119 req.nlh.nlmsg_seq = ++sequence;
120
121 /* While failing and its due to interrupts */
122
123 rc = TEMP_FAILURE_RETRY(sendto(fd, &req, req.nlh.nlmsg_len, 0,
124 (struct sockaddr*)&addr, sizeof(addr)));
125
126 /* Not all the bytes were sent */
127 if (rc < 0) {
128 rc = -errno;
129 goto out;
130 } else if ((uint32_t)rc != req.nlh.nlmsg_len) {
131 rc = -EPROTO;
132 goto out;
133 }
134
135 /* We sent all the bytes, get the ack */
136 rc = get_ack(fd);
137
138 /* If the ack failed, return the error, else return the sequence number */
139 rc = (rc == 0) ? (int)sequence : rc;
140
141 out:
142 /* Don't let sequence roll to negative */
143 if (sequence < 0) {
144 sequence = 0;
145 }
146
147 return rc;
148 }
149
audit_setup(int fd,pid_t pid)150 int audit_setup(int fd, pid_t pid) {
151 int rc;
152 struct audit_message rep;
153 struct audit_status status;
154
155 memset(&status, 0, sizeof(status));
156
157 /*
158 * In order to set the auditd PID we send an audit message over the netlink
159 * socket with the pid field of the status struct set to our current pid,
160 * and the the mask set to AUDIT_STATUS_PID
161 */
162 status.pid = pid;
163 status.mask = AUDIT_STATUS_PID;
164
165 /* Let the kernel know this pid will be registering for audit events */
166 rc = audit_send(fd, AUDIT_SET, &status, sizeof(status));
167 if (rc < 0) {
168 return rc;
169 }
170
171 /*
172 * In a request where we need to wait for a response, wait for the message
173 * and discard it. This message confirms and sync's us with the kernel.
174 * This daemon is now registered as the audit logger.
175 *
176 * TODO
177 * If the daemon dies and restarts the message didn't come back,
178 * so I went to non-blocking and it seemed to fix the bug.
179 * Need to investigate further.
180 */
181 audit_get_reply(fd, &rep, GET_REPLY_NONBLOCKING, 0);
182
183 return 0;
184 }
185
audit_open()186 int audit_open() {
187 return socket(PF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_AUDIT);
188 }
189
audit_rate_limit(int fd,uint32_t limit)190 int audit_rate_limit(int fd, uint32_t limit) {
191 struct audit_status status;
192 memset(&status, 0, sizeof(status));
193 status.mask = AUDIT_STATUS_RATE_LIMIT;
194 status.rate_limit = limit; /* audit entries per second */
195 return audit_send(fd, AUDIT_SET, &status, sizeof(status));
196 }
197
audit_get_reply(int fd,struct audit_message * rep,reply_t block,int peek)198 int audit_get_reply(int fd, struct audit_message* rep, reply_t block, int peek) {
199 ssize_t len;
200 int flags;
201 int rc = 0;
202
203 struct sockaddr_nl nladdr;
204 socklen_t nladdrlen = sizeof(nladdr);
205
206 if (fd < 0) {
207 return -EBADF;
208 }
209
210 /* Set up the flags for recv from */
211 flags = (block == GET_REPLY_NONBLOCKING) ? MSG_DONTWAIT : 0;
212 flags |= peek;
213
214 /*
215 * Get the data from the netlink socket but on error we need to be carefull,
216 * the interface shows that EINTR can never be returned, other errors,
217 * however, can be returned.
218 */
219 len = TEMP_FAILURE_RETRY(recvfrom(fd, rep, sizeof(*rep), flags,
220 (struct sockaddr*)&nladdr, &nladdrlen));
221
222 /*
223 * EAGAIN should be re-tried until success or another error manifests.
224 */
225 if (len < 0) {
226 rc = -errno;
227 if (block == GET_REPLY_NONBLOCKING && rc == -EAGAIN) {
228 /* If request is non blocking and errno is EAGAIN, just return 0 */
229 return 0;
230 }
231 return rc;
232 }
233
234 if (nladdrlen != sizeof(nladdr)) {
235 return -EPROTO;
236 }
237
238 /* Make sure the netlink message was not spoof'd */
239 if (nladdr.nl_pid) {
240 return -EINVAL;
241 }
242
243 /* Check if the reply from the kernel was ok */
244 if (!NLMSG_OK(&rep->nlh, (size_t)len)) {
245 rc = (len == sizeof(*rep)) ? -EFBIG : -EBADE;
246 }
247
248 return rc;
249 }
250
audit_close(int fd)251 void audit_close(int fd) {
252 close(fd);
253 }
254