Fold uevent message origin checking from init into libcutils.
Change-Id: I7cbc0cb840d1b4962e6c360fdad9a9c0ce20e87b
diff --git a/libcutils/uevent.c b/libcutils/uevent.c
new file mode 100644
index 0000000..3533c00
--- /dev/null
+++ b/libcutils/uevent.c
@@ -0,0 +1,70 @@
+/*
+ * 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;
+}