1 /*
2 * Copyright (C) 2011 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 <cutils/uevent.h>
18
19 #include <errno.h>
20 #include <stdbool.h>
21 #include <string.h>
22 #include <strings.h>
23 #include <sys/socket.h>
24 #include <sys/un.h>
25 #include <unistd.h>
26
27 #include <linux/netlink.h>
28
29 /**
30 * Like recv(), but checks that messages actually originate from the kernel.
31 */
uevent_kernel_multicast_recv(int socket,void * buffer,size_t length)32 ssize_t uevent_kernel_multicast_recv(int socket, void *buffer, size_t length) {
33 struct iovec iov = { buffer, length };
34 struct sockaddr_nl addr;
35 char control[CMSG_SPACE(sizeof(struct ucred))];
36 struct msghdr hdr = {
37 &addr,
38 sizeof(addr),
39 &iov,
40 1,
41 control,
42 sizeof(control),
43 0,
44 };
45
46 ssize_t n = recvmsg(socket, &hdr, 0);
47 if (n <= 0) {
48 return n;
49 }
50
51 if (addr.nl_groups == 0 || addr.nl_pid != 0) {
52 /* ignoring non-kernel or unicast netlink message */
53 goto out;
54 }
55
56 struct cmsghdr *cmsg = CMSG_FIRSTHDR(&hdr);
57 if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
58 /* ignoring netlink message with no sender credentials */
59 goto out;
60 }
61
62 struct ucred *cred = (struct ucred *)CMSG_DATA(cmsg);
63 if (cred->uid != 0) {
64 /* ignoring netlink message from non-root user */
65 goto out;
66 }
67
68 return n;
69
70 out:
71 /* clear residual potentially malicious data */
72 bzero(buffer, length);
73 errno = EIO;
74 return -1;
75 }
76
uevent_open_socket(int buf_sz,bool passcred)77 int uevent_open_socket(int buf_sz, bool passcred)
78 {
79 struct sockaddr_nl addr;
80 int on = passcred;
81 int s;
82
83 memset(&addr, 0, sizeof(addr));
84 addr.nl_family = AF_NETLINK;
85 addr.nl_pid = getpid();
86 addr.nl_groups = 0xffffffff;
87
88 s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
89 if(s < 0)
90 return -1;
91
92 setsockopt(s, SOL_SOCKET, SO_RCVBUFFORCE, &buf_sz, sizeof(buf_sz));
93 setsockopt(s, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
94
95 if(bind(s, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
96 close(s);
97 return -1;
98 }
99
100 return s;
101 }
102