Fold uevent message origin checking from init into libcutils. (8405ec0e) · Commits · e / os / android_system_core

include/cutils/uevent.h

0 → 100644

+32 −0

Original line number	Diff line number	Diff line
		/*
		* 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.
		*/

		#ifndef __CUTILS_UEVENT_H
		#define __CUTILS_UEVENT_H

		#include <sys/socket.h>

		#ifdef __cplusplus
		extern "C" {
		#endif

		ssize_t uevent_checked_recv(int socket, void *buffer, size_t length);

		#ifdef __cplusplus
		}
		#endif

		#endif /* __CUTILS_UEVENT_H */

init/devices.c

+5 −29

Original line number	Diff line number	Diff line
		@@ -33,6 +33,8 @@
		#include <asm/page.h>
		#include <sys/wait.h>

		#include <cutils/uevent.h>

		#include "devices.h"
		#include "util.h"
		#include "log.h"
		@@ -589,35 +591,9 @@ static void handle_firmware_event(struct uevent *uevent)
		#define UEVENT_MSG_LEN 1024
		void handle_device_fd()
		{
		for(;;) {
		char msg[UEVENT_MSG_LEN+2];
		char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
		struct iovec iov = {msg, sizeof(msg)};
		struct sockaddr_nl snl;
		struct msghdr hdr = {&snl, sizeof(snl), &iov, 1, cred_msg, sizeof(cred_msg), 0};

		ssize_t n = recvmsg(device_fd, &hdr, 0);
		if (n <= 0) {
		break;
		}

		if ((snl.nl_groups != 1) \|\| (snl.nl_pid != 0)) {
		/* ignoring non-kernel netlink multicast message */
		continue;
		}

		struct cmsghdr * cmsg = CMSG_FIRSTHDR(&hdr);
		if (cmsg == NULL \|\| cmsg->cmsg_type != SCM_CREDENTIALS) {
		/* no sender credentials received, ignore message */
		continue;
		}

		struct ucred * cred = (struct ucred *)CMSG_DATA(cmsg);
		if (cred->uid != 0) {
		/* message from non-root user, ignore */
		continue;
		}

		int n;
		while ((n = uevent_checked_recv(device_fd, msg, UEVENT_MSG_LEN)) > 0) {
		if(n >= UEVENT_MSG_LEN) /* overflow -- discard */
		continue;

libcutils/Android.mk

+1 −0

Original line number	Diff line number	Diff line
		@@ -74,6 +74,7 @@ else
		mspace.c \
		selector.c \
		tztime.c \
		uevent.c \
		zygote.c

		commonHostSources += \

libcutils/uevent.c

0 → 100644

+70 −0

Original line number	Diff line number	Diff line
		/*
		* 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;
		}