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 {
34 uid_t user = -1;
35 return uevent_kernel_multicast_uid_recv(socket, buffer, length, &user);
36 }
37
38 /**
39 * Like the above, but passes a uid_t in by reference. In the event that this
40 * fails due to a bad uid check, the uid_t will be set to the uid of the
41 * socket's peer.
42 *
43 * If this method rejects a netlink message from outside the kernel, it
44 * returns -1, sets errno to EIO, and sets "user" to the UID associated with the
45 * message. If the peer UID cannot be determined, "user" is set to -1."
46 */
uevent_kernel_multicast_uid_recv(int socket,void * buffer,size_t length,uid_t * user)47 ssize_t uevent_kernel_multicast_uid_recv(int socket, void *buffer,
48 size_t length, uid_t *user)
49 {
50 struct iovec iov = { buffer, length };
51 struct sockaddr_nl addr;
52 char control[CMSG_SPACE(sizeof(struct ucred))];
53 struct msghdr hdr = {
54 &addr,
55 sizeof(addr),
56 &iov,
57 1,
58 control,
59 sizeof(control),
60 0,
61 };
62
63 *user = -1;
64 ssize_t n = recvmsg(socket, &hdr, 0);
65 if (n <= 0) {
66 return n;
67 }
68
69 struct cmsghdr *cmsg = CMSG_FIRSTHDR(&hdr);
70 if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
71 /* ignoring netlink message with no sender credentials */
72 goto out;
73 }
74
75 struct ucred *cred = (struct ucred *)CMSG_DATA(cmsg);
76 *user = cred->uid;
77 if (cred->uid != 0) {
78 /* ignoring netlink message from non-root user */
79 goto out;
80 }
81
82 if (addr.nl_groups == 0 || addr.nl_pid != 0) {
83 /* ignoring non-kernel or unicast netlink message */
84 goto out;
85 }
86
87 return n;
88
89 out:
90 /* clear residual potentially malicious data */
91 bzero(buffer, length);
92 errno = EIO;
93 return -1;
94 }
95
uevent_open_socket(int buf_sz,bool passcred)96 int uevent_open_socket(int buf_sz, bool passcred)
97 {
98 struct sockaddr_nl addr;
99 int on = passcred;
100 int s;
101
102 memset(&addr, 0, sizeof(addr));
103 addr.nl_family = AF_NETLINK;
104 addr.nl_pid = getpid();
105 addr.nl_groups = 0xffffffff;
106
107 s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
108 if(s < 0)
109 return -1;
110
111 setsockopt(s, SOL_SOCKET, SO_RCVBUFFORCE, &buf_sz, sizeof(buf_sz));
112 setsockopt(s, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
113
114 if(bind(s, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
115 close(s);
116 return -1;
117 }
118
119 return s;
120 }
121