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 uid = -1;
35 return uevent_kernel_multicast_uid_recv(socket, buffer, length, &uid);
36 }
37
38 /**
39 * Like the above, but passes a uid_t in by pointer. 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 * uid)47 ssize_t uevent_kernel_multicast_uid_recv(int socket, void *buffer, size_t length, uid_t *uid)
48 {
49 return uevent_kernel_recv(socket, buffer, length, true, uid);
50 }
51
uevent_kernel_recv(int socket,void * buffer,size_t length,bool require_group,uid_t * uid)52 ssize_t uevent_kernel_recv(int socket, void *buffer, size_t length, bool require_group, uid_t *uid)
53 {
54 struct iovec iov = { buffer, length };
55 struct sockaddr_nl addr;
56 char control[CMSG_SPACE(sizeof(struct ucred))];
57 struct msghdr hdr = {
58 &addr,
59 sizeof(addr),
60 &iov,
61 1,
62 control,
63 sizeof(control),
64 0,
65 };
66
67 *uid = -1;
68 ssize_t n = recvmsg(socket, &hdr, 0);
69 if (n <= 0) {
70 return n;
71 }
72
73 struct cmsghdr *cmsg = CMSG_FIRSTHDR(&hdr);
74 if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
75 /* ignoring netlink message with no sender credentials */
76 goto out;
77 }
78
79 struct ucred *cred = (struct ucred *)CMSG_DATA(cmsg);
80 *uid = cred->uid;
81 if (cred->uid != 0) {
82 /* ignoring netlink message from non-root user */
83 goto out;
84 }
85
86 if (addr.nl_pid != 0) {
87 /* ignore non-kernel */
88 goto out;
89 }
90 if (require_group && addr.nl_groups == 0) {
91 /* ignore unicast messages when requested */
92 goto out;
93 }
94
95 return n;
96
97 out:
98 /* clear residual potentially malicious data */
99 bzero(buffer, length);
100 errno = EIO;
101 return -1;
102 }
103
uevent_open_socket(int buf_sz,bool passcred)104 int uevent_open_socket(int buf_sz, bool passcred)
105 {
106 struct sockaddr_nl addr;
107 int on = passcred;
108 int s;
109
110 memset(&addr, 0, sizeof(addr));
111 addr.nl_family = AF_NETLINK;
112 addr.nl_pid = getpid();
113 addr.nl_groups = 0xffffffff;
114
115 s = socket(PF_NETLINK, SOCK_DGRAM | SOCK_CLOEXEC, NETLINK_KOBJECT_UEVENT);
116 if(s < 0)
117 return -1;
118
119 /* buf_sz should be less than net.core.rmem_max for this to succeed */
120 if (setsockopt(s, SOL_SOCKET, SO_RCVBUF, &buf_sz, sizeof(buf_sz)) < 0) {
121 close(s);
122 return -1;
123 }
124
125 setsockopt(s, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
126
127 if(bind(s, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
128 close(s);
129 return -1;
130 }
131
132 return s;
133 }
134