Vernon Tang | 3f582e9 | 2011-04-25 13:08:17 +1000 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2011 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | #include <cutils/uevent.h> |
| 18 | |
| 19 | #include <errno.h> |
| 20 | #include <strings.h> |
| 21 | |
| 22 | #include <linux/netlink.h> |
| 23 | |
| 24 | /** |
| 25 | * Like recv(), but checks that messages actually originate from the kernel. |
| 26 | */ |
| 27 | ssize_t uevent_checked_recv(int socket, void *buffer, size_t length) { |
| 28 | struct iovec iov = { buffer, length }; |
| 29 | struct sockaddr_nl addr; |
| 30 | char control[CMSG_SPACE(sizeof(struct ucred))]; |
| 31 | struct msghdr hdr = { |
| 32 | &addr, |
| 33 | sizeof(addr), |
| 34 | &iov, |
| 35 | 1, |
| 36 | control, |
| 37 | sizeof(control), |
| 38 | 0, |
| 39 | }; |
| 40 | |
| 41 | ssize_t n = recvmsg(socket, &hdr, 0); |
| 42 | if (n <= 0) { |
| 43 | return n; |
| 44 | } |
| 45 | |
| 46 | if (addr.nl_groups == 0 || addr.nl_pid != 0) { |
| 47 | /* ignoring non-kernel or unicast netlink message */ |
| 48 | goto out; |
| 49 | } |
| 50 | |
| 51 | struct cmsghdr *cmsg = CMSG_FIRSTHDR(&hdr); |
| 52 | if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) { |
| 53 | /* ignoring netlink message with no sender credentials */ |
| 54 | goto out; |
| 55 | } |
| 56 | |
| 57 | struct ucred *cred = (struct ucred *)CMSG_DATA(cmsg); |
| 58 | if (cred->uid != 0) { |
| 59 | /* ignoring netlink message from non-root user */ |
| 60 | goto out; |
| 61 | } |
| 62 | |
| 63 | return n; |
| 64 | |
| 65 | out: |
| 66 | /* clear residual potentially malicious data */ |
| 67 | bzero(buffer, length); |
| 68 | errno = EIO; |
| 69 | return -1; |
| 70 | } |