diff --git a/include/cutils/uevent.h b/include/cutils/uevent.h new file mode 100644 index 000000000..587149c7d --- /dev/null +++ b/include/cutils/uevent.h @@ -0,0 +1,32 @@ +/* + * 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 + +#ifdef __cplusplus +extern "C" { +#endif + +ssize_t uevent_checked_recv(int socket, void *buffer, size_t length); + +#ifdef __cplusplus +} +#endif + +#endif /* __CUTILS_UEVENT_H */ diff --git a/init/devices.c b/init/devices.c index e73efdf03..eb5d84e05 100644 --- a/init/devices.c +++ b/init/devices.c @@ -33,6 +33,8 @@ #include #include +#include + #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; - } - + char msg[UEVENT_MSG_LEN+2]; + int n; + while ((n = uevent_checked_recv(device_fd, msg, UEVENT_MSG_LEN)) > 0) { if(n >= UEVENT_MSG_LEN) /* overflow -- discard */ continue; diff --git a/libcutils/Android.mk b/libcutils/Android.mk index 3dc3d694a..1951c1df0 100644 --- a/libcutils/Android.mk +++ b/libcutils/Android.mk @@ -74,6 +74,7 @@ else mspace.c \ selector.c \ tztime.c \ + uevent.c \ zygote.c commonHostSources += \ diff --git a/libcutils/uevent.c b/libcutils/uevent.c new file mode 100644 index 000000000..3533c00f6 --- /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 + +#include +#include + +#include + +/** + * 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; +}