summaryrefslogtreecommitdiffstats
blob: 2dfceede5bbd968fa55447ac1f18d7e8acf840c2 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <cutils/uevent.h>

#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>

#include <linux/netlink.h>

extern "C" {

/**
 * Like recv(), but checks that messages actually originate from the kernel.
 */
ssize_t uevent_kernel_multicast_recv(int socket, void* buffer, size_t length) {
    uid_t uid = -1;
    return uevent_kernel_multicast_uid_recv(socket, buffer, length, &uid);
}

/**
 * Like the above, but passes a uid_t in by pointer. In the event that this
 * fails due to a bad uid check, the uid_t will be set to the uid of the
 * socket's peer.
 *
 * If this method rejects a netlink message from outside the kernel, it
 * returns -1, sets errno to EIO, and sets "user" to the UID associated with the
 * message. If the peer UID cannot be determined, "user" is set to -1."
 */
ssize_t uevent_kernel_multicast_uid_recv(int socket, void* buffer, size_t length, uid_t* uid) {
    return uevent_kernel_recv(socket, buffer, length, true, uid);
}

ssize_t uevent_kernel_recv(int socket, void* buffer, size_t length, bool require_group, uid_t* uid) {
    struct iovec iov = {buffer, length};
    struct sockaddr_nl addr;
    char control[CMSG_SPACE(sizeof(struct ucred))];
    struct msghdr hdr = {
        &addr, sizeof(addr), &iov, 1, control, sizeof(control), 0,
    };
    struct ucred* cred;

    *uid = -1;
    ssize_t n = recvmsg(socket, &hdr, 0);
    if (n <= 0) {
        return n;
    }

    struct cmsghdr* cmsg = CMSG_FIRSTHDR(&hdr);
    if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
        /* ignoring netlink message with no sender credentials */
        goto out;
    }

    cred = (struct ucred*)CMSG_DATA(cmsg);
    *uid = cred->uid;

    if (addr.nl_pid != 0) {
        /* ignore non-kernel */
        goto out;
    }
    if (require_group && addr.nl_groups == 0) {
        /* ignore unicast messages when requested */
        goto out;
    }

    return n;

out:
    /* clear residual potentially malicious data */
    bzero(buffer, length);
    errno = EIO;
    return -1;
}

int uevent_open_socket(int buf_sz, bool passcred) {
    struct sockaddr_nl addr;
    int on = passcred;
    int s;

    memset(&addr, 0, sizeof(addr));
    addr.nl_family = AF_NETLINK;
    addr.nl_pid = getpid();
    addr.nl_groups = 0xffffffff;

    s = socket(PF_NETLINK, SOCK_DGRAM | SOCK_CLOEXEC, NETLINK_KOBJECT_UEVENT);
    if (s < 0) return -1;

    /* buf_sz should be less than net.core.rmem_max for this to succeed */
    if (setsockopt(s, SOL_SOCKET, SO_RCVBUF, &buf_sz, sizeof(buf_sz)) < 0) {
        close(s);
        return -1;
    }

    setsockopt(s, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));

    if (bind(s, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
        close(s);
        return -1;
    }

    return s;
}

}  // extern "C"