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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 user = -1;
- return uevent_kernel_multicast_uid_recv(socket, buffer, length, &user);
- }
- /**
- * Like the above, but passes a uid_t in by reference. 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 *user)
- {
- 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,
- };
- *user = -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);
- *user = cred->uid;
- if (cred->uid != 0) {
- /* ignoring netlink message from non-root user */
- goto out;
- }
- if (addr.nl_groups == 0 || addr.nl_pid != 0) {
- /* ignoring non-kernel or unicast netlink message */
- 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, 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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