70 lines
1.8 KiB
C
70 lines
1.8 KiB
C
/*
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* Copyright (C) 2011 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <cutils/uevent.h>
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#include <errno.h>
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#include <strings.h>
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#include <linux/netlink.h>
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/**
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* Like recv(), but checks that messages actually originate from the kernel.
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*/
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ssize_t uevent_kernel_multicast_recv(int socket, void *buffer, size_t length) {
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struct iovec iov = { buffer, length };
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struct sockaddr_nl addr;
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char control[CMSG_SPACE(sizeof(struct ucred))];
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struct msghdr hdr = {
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&addr,
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sizeof(addr),
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&iov,
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1,
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control,
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sizeof(control),
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0,
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};
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ssize_t n = recvmsg(socket, &hdr, 0);
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if (n <= 0) {
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return n;
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}
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if (addr.nl_groups == 0 || addr.nl_pid != 0) {
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/* ignoring non-kernel or unicast netlink message */
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goto out;
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}
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struct cmsghdr *cmsg = CMSG_FIRSTHDR(&hdr);
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if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
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/* ignoring netlink message with no sender credentials */
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goto out;
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}
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struct ucred *cred = (struct ucred *)CMSG_DATA(cmsg);
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if (cred->uid != 0) {
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/* ignoring netlink message from non-root user */
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goto out;
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}
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return n;
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out:
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/* clear residual potentially malicious data */
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bzero(buffer, length);
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errno = EIO;
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return -1;
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}
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