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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 <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;
}
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