uevent.c revision 2d55e02d0f3c27f0c99ab889ab7b73126280a21c 
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 */
32ssize_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
70out:
71    /* clear residual potentially malicious data */
72    bzero(buffer, length);
73    errno = EIO;
74    return -1;
75}
76
77int 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