70 lines
1.8 KiB
C
70 lines
1.8 KiB
C
/*
|
|
* 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 <strings.h>
|
|
|
|
#include <linux/netlink.h>
|
|
|
|
/**
|
|
* Like recv(), but checks that messages actually originate from the kernel.
|
|
*/
|
|
ssize_t uevent_checked_recv(int socket, void *buffer, size_t length) {
|
|
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,
|
|
};
|
|
|
|
ssize_t n = recvmsg(socket, &hdr, 0);
|
|
if (n <= 0) {
|
|
return n;
|
|
}
|
|
|
|
if (addr.nl_groups == 0 || addr.nl_pid != 0) {
|
|
/* ignoring non-kernel or unicast netlink message */
|
|
goto out;
|
|
}
|
|
|
|
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);
|
|
if (cred->uid != 0) {
|
|
/* ignoring netlink message from non-root user */
|
|
goto out;
|
|
}
|
|
|
|
return n;
|
|
|
|
out:
|
|
/* clear residual potentially malicious data */
|
|
bzero(buffer, length);
|
|
errno = EIO;
|
|
return -1;
|
|
}
|