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/*
* 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 <stdbool.h>
#include <string.h>
#include <strings.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>
#include <linux/netlink.h>
/**
* 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,
};
*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;
}
struct ucred *cred = (struct ucred *)CMSG_DATA(cmsg);
*uid = cred->uid;
if (cred->uid != 0) {
/* ignoring netlink message from non-root user */
goto out;
}
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;
setsockopt(s, SOL_SOCKET, SO_RCVBUFFORCE, &buf_sz, sizeof(buf_sz));
setsockopt(s, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
if(bind(s, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
close(s);
return -1;
}
return s;
}
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