Martin Stjernholm | 4fb5111 | 2021-04-30 11:53:52 +0100 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2019 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 | #pragma once |
| 18 | |
| 19 | #include <sys/stat.h> |
| 20 | #include <sys/types.h> |
| 21 | |
| 22 | #include <type_traits> |
| 23 | #include <vector> |
| 24 | |
| 25 | #include <android-base/collections.h> |
| 26 | #include <android-base/macros.h> |
| 27 | #include <android-base/unique_fd.h> |
| 28 | |
| 29 | namespace android { |
| 30 | namespace base { |
| 31 | |
| 32 | #if !defined(_WIN32) |
| 33 | |
| 34 | // Helpers for sending and receiving file descriptors across Unix domain sockets. |
| 35 | // |
| 36 | // The cmsg(3) API is very hard to get right, with multiple landmines that can |
| 37 | // lead to death. Almost all of the uses of cmsg in Android make at least one of |
| 38 | // the following mistakes: |
| 39 | // |
| 40 | // - not aligning the cmsg buffer |
| 41 | // - leaking fds if more fds are received than expected |
| 42 | // - blindly dereferencing CMSG_DATA without checking the header |
| 43 | // - using CMSG_SPACE instead of CMSG_LEN for .cmsg_len |
| 44 | // - using CMSG_LEN instead of CMSG_SPACE for .msg_controllen |
| 45 | // - using a length specified in number of fds instead of bytes |
| 46 | // |
| 47 | // These functions wrap the hard-to-use cmsg API with an easier to use abstraction. |
| 48 | |
| 49 | // Send file descriptors across a Unix domain socket. |
| 50 | // |
| 51 | // Note that the write can return short if the socket type is SOCK_STREAM. When |
| 52 | // this happens, file descriptors are still sent to the other end, but with |
| 53 | // truncated data. For this reason, using SOCK_SEQPACKET or SOCK_DGRAM is recommended. |
| 54 | ssize_t SendFileDescriptorVector(borrowed_fd sock, const void* data, size_t len, |
| 55 | const std::vector<int>& fds); |
| 56 | |
| 57 | // Receive file descriptors from a Unix domain socket. |
| 58 | // |
| 59 | // If more FDs (or bytes, for datagram sockets) are received than expected, |
| 60 | // -1 is returned with errno set to EMSGSIZE, and all received FDs are thrown away. |
| 61 | ssize_t ReceiveFileDescriptorVector(borrowed_fd sock, void* data, size_t len, size_t max_fds, |
| 62 | std::vector<android::base::unique_fd>* fds); |
| 63 | |
| 64 | // Helper for SendFileDescriptorVector that constructs a std::vector for you, e.g.: |
| 65 | // SendFileDescriptors(sock, "foo", 3, std::move(fd1), std::move(fd2)) |
| 66 | template <typename... Args> |
| 67 | ssize_t SendFileDescriptors(borrowed_fd sock, const void* data, size_t len, Args&&... sent_fds) { |
| 68 | // Do not allow implicit conversion to int: people might try to do something along the lines of: |
| 69 | // SendFileDescriptors(..., std::move(a_unique_fd)) |
| 70 | // and be surprised when the unique_fd isn't closed afterwards. |
| 71 | AssertType<int>(std::forward<Args>(sent_fds)...); |
| 72 | std::vector<int> fds; |
| 73 | Append(fds, std::forward<Args>(sent_fds)...); |
| 74 | return SendFileDescriptorVector(sock, data, len, fds); |
| 75 | } |
| 76 | |
| 77 | // Helper for ReceiveFileDescriptorVector that receives an exact number of file descriptors. |
| 78 | // If more file descriptors are received than requested, -1 is returned with errno set to EMSGSIZE. |
| 79 | // If fewer file descriptors are received than requested, -1 is returned with errno set to ENOMSG. |
| 80 | // In both cases, all arguments are cleared and any received FDs are thrown away. |
| 81 | template <typename... Args> |
| 82 | ssize_t ReceiveFileDescriptors(borrowed_fd sock, void* data, size_t len, Args&&... received_fds) { |
| 83 | std::vector<unique_fd*> fds; |
| 84 | Append(fds, std::forward<Args>(received_fds)...); |
| 85 | |
| 86 | std::vector<unique_fd> result; |
| 87 | ssize_t rc = ReceiveFileDescriptorVector(sock, data, len, fds.size(), &result); |
| 88 | if (rc == -1 || result.size() != fds.size()) { |
| 89 | int err = rc == -1 ? errno : ENOMSG; |
| 90 | for (unique_fd* fd : fds) { |
| 91 | fd->reset(); |
| 92 | } |
| 93 | errno = err; |
| 94 | return -1; |
| 95 | } |
| 96 | |
| 97 | for (size_t i = 0; i < fds.size(); ++i) { |
| 98 | *fds[i] = std::move(result[i]); |
| 99 | } |
| 100 | return rc; |
| 101 | } |
| 102 | |
| 103 | #endif |
| 104 | |
| 105 | } // namespace base |
| 106 | } // namespace android |