134 lines
3.5 KiB
C
134 lines
3.5 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 <stdbool.h>
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#include <string.h>
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#include <strings.h>
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#include <sys/socket.h>
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#include <sys/un.h>
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#include <unistd.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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{
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uid_t uid = -1;
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return uevent_kernel_multicast_uid_recv(socket, buffer, length, &uid);
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}
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/**
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* Like the above, but passes a uid_t in by pointer. In the event that this
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* fails due to a bad uid check, the uid_t will be set to the uid of the
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* socket's peer.
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*
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* If this method rejects a netlink message from outside the kernel, it
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* returns -1, sets errno to EIO, and sets "user" to the UID associated with the
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* message. If the peer UID cannot be determined, "user" is set to -1."
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*/
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ssize_t uevent_kernel_multicast_uid_recv(int socket, void *buffer, size_t length, uid_t *uid)
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{
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return uevent_kernel_recv(socket, buffer, length, true, uid);
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}
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ssize_t uevent_kernel_recv(int socket, void *buffer, size_t length, bool require_group, uid_t *uid)
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{
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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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*uid = -1;
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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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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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*uid = cred->uid;
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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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if (addr.nl_pid != 0) {
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/* ignore non-kernel */
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goto out;
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}
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if (require_group && addr.nl_groups == 0) {
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/* ignore unicast messages when requested */
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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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int uevent_open_socket(int buf_sz, bool passcred)
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{
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struct sockaddr_nl addr;
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int on = passcred;
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int s;
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memset(&addr, 0, sizeof(addr));
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addr.nl_family = AF_NETLINK;
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addr.nl_pid = getpid();
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addr.nl_groups = 0xffffffff;
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s = socket(PF_NETLINK, SOCK_DGRAM | SOCK_CLOEXEC, NETLINK_KOBJECT_UEVENT);
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if(s < 0)
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return -1;
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/* buf_sz should be less than net.core.rmem_max for this to succeed */
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if (setsockopt(s, SOL_SOCKET, SO_RCVBUF, &buf_sz, sizeof(buf_sz)) < 0) {
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close(s);
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return -1;
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}
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setsockopt(s, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
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if(bind(s, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
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close(s);
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return -1;
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}
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return s;
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}
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