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107 lines
4.1 KiB
107 lines
4.1 KiB
4 months ago
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/*
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* Copyright (C) 2019 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <type_traits>
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#include <vector>
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#include <android-base/collections.h>
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#include <android-base/macros.h>
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#include <android-base/unique_fd.h>
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namespace android {
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namespace base {
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#if !defined(_WIN32)
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// Helpers for sending and receiving file descriptors across Unix domain sockets.
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//
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// The cmsg(3) API is very hard to get right, with multiple landmines that can
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// lead to death. Almost all of the uses of cmsg in Android make at least one of
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// the following mistakes:
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//
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// - not aligning the cmsg buffer
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// - leaking fds if more fds are received than expected
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// - blindly dereferencing CMSG_DATA without checking the header
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// - using CMSG_SPACE instead of CMSG_LEN for .cmsg_len
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// - using CMSG_LEN instead of CMSG_SPACE for .msg_controllen
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// - using a length specified in number of fds instead of bytes
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//
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// These functions wrap the hard-to-use cmsg API with an easier to use abstraction.
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// Send file descriptors across a Unix domain socket.
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//
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// Note that the write can return short if the socket type is SOCK_STREAM. When
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// this happens, file descriptors are still sent to the other end, but with
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// truncated data. For this reason, using SOCK_SEQPACKET or SOCK_DGRAM is recommended.
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ssize_t SendFileDescriptorVector(borrowed_fd sock, const void* data, size_t len,
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const std::vector<int>& fds);
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// Receive file descriptors from a Unix domain socket.
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//
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// If more FDs (or bytes, for datagram sockets) are received than expected,
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// -1 is returned with errno set to EMSGSIZE, and all received FDs are thrown away.
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ssize_t ReceiveFileDescriptorVector(borrowed_fd sock, void* data, size_t len, size_t max_fds,
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std::vector<android::base::unique_fd>* fds);
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// Helper for SendFileDescriptorVector that constructs a std::vector for you, e.g.:
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// SendFileDescriptors(sock, "foo", 3, std::move(fd1), std::move(fd2))
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template <typename... Args>
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ssize_t SendFileDescriptors(borrowed_fd sock, const void* data, size_t len, Args&&... sent_fds) {
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// Do not allow implicit conversion to int: people might try to do something along the lines of:
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// SendFileDescriptors(..., std::move(a_unique_fd))
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// and be surprised when the unique_fd isn't closed afterwards.
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AssertType<int>(std::forward<Args>(sent_fds)...);
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std::vector<int> fds;
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Append(fds, std::forward<Args>(sent_fds)...);
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return SendFileDescriptorVector(sock, data, len, fds);
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}
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// Helper for ReceiveFileDescriptorVector that receives an exact number of file descriptors.
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// If more file descriptors are received than requested, -1 is returned with errno set to EMSGSIZE.
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// If fewer file descriptors are received than requested, -1 is returned with errno set to ENOMSG.
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// In both cases, all arguments are cleared and any received FDs are thrown away.
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template <typename... Args>
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ssize_t ReceiveFileDescriptors(borrowed_fd sock, void* data, size_t len, Args&&... received_fds) {
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std::vector<unique_fd*> fds;
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Append(fds, std::forward<Args>(received_fds)...);
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std::vector<unique_fd> result;
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ssize_t rc = ReceiveFileDescriptorVector(sock, data, len, fds.size(), &result);
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if (rc == -1 || result.size() != fds.size()) {
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int err = rc == -1 ? errno : ENOMSG;
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for (unique_fd* fd : fds) {
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fd->reset();
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}
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errno = err;
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return -1;
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}
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for (size_t i = 0; i < fds.size(); ++i) {
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*fds[i] = std::move(result[i]);
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}
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return rc;
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}
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#endif
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} // namespace base
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} // namespace android
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