1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
|
/*
* Copyright (C) 2019 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.
*/
#pragma once
#include <sys/stat.h>
#include <sys/types.h>
#include <type_traits>
#include <vector>
#include <android-base/collections.h>
#include <android-base/macros.h>
#include <android-base/unique_fd.h>
namespace android {
namespace base {
#if !defined(_WIN32)
// Helpers for sending and receiving file descriptors across Unix domain sockets.
//
// The cmsg(3) API is very hard to get right, with multiple landmines that can
// lead to death. Almost all of the uses of cmsg in Android make at least one of
// the following mistakes:
//
// - not aligning the cmsg buffer
// - leaking fds if more fds are received than expected
// - blindly dereferencing CMSG_DATA without checking the header
// - using CMSG_SPACE instead of CMSG_LEN for .cmsg_len
// - using CMSG_LEN instead of CMSG_SPACE for .msg_controllen
// - using a length specified in number of fds instead of bytes
//
// These functions wrap the hard-to-use cmsg API with an easier to use abstraction.
// Send file descriptors across a Unix domain socket.
//
// Note that the write can return short if the socket type is SOCK_STREAM. When
// this happens, file descriptors are still sent to the other end, but with
// truncated data. For this reason, using SOCK_SEQPACKET or SOCK_DGRAM is recommended.
ssize_t SendFileDescriptorVector(int sock, const void* data, size_t len,
const std::vector<int>& fds);
// Receive file descriptors from a Unix domain socket.
//
// If more FDs (or bytes, for datagram sockets) are received than expected,
// -1 is returned with errno set to EMSGSIZE, and all received FDs are thrown away.
ssize_t ReceiveFileDescriptorVector(int sock, void* data, size_t len, size_t max_fds,
std::vector<android::base::unique_fd>* fds);
// Helper for SendFileDescriptorVector that constructs a std::vector for you, e.g.:
// SendFileDescriptors(sock, "foo", 3, std::move(fd1), std::move(fd2))
template <typename... Args>
ssize_t SendFileDescriptors(int sock, const void* data, size_t len, Args&&... sent_fds) {
// Do not allow implicit conversion to int: people might try to do something along the lines of:
// SendFileDescriptors(..., std::move(a_unique_fd))
// and be surprised when the unique_fd isn't closed afterwards.
AssertType<int>(std::forward<Args>(sent_fds)...);
std::vector<int> fds;
Append(fds, std::forward<Args>(sent_fds)...);
return SendFileDescriptorVector(sock, data, len, fds);
}
// Helper for ReceiveFileDescriptorVector that receives an exact number of file descriptors.
// If more file descriptors are received than requested, -1 is returned with errno set to EMSGSIZE.
// If fewer file descriptors are received than requested, -1 is returned with errno set to ENOMSG.
// In both cases, all arguments are cleared and any received FDs are thrown away.
template <typename... Args>
ssize_t ReceiveFileDescriptors(int sock, void* data, size_t len, Args&&... received_fds) {
std::vector<unique_fd*> fds;
Append(fds, std::forward<Args>(received_fds)...);
std::vector<unique_fd> result;
ssize_t rc = ReceiveFileDescriptorVector(sock, data, len, fds.size(), &result);
if (rc == -1 || result.size() != fds.size()) {
int err = rc == -1 ? errno : ENOMSG;
for (unique_fd* fd : fds) {
fd->reset();
}
errno = err;
return -1;
}
for (size_t i = 0; i < fds.size(); ++i) {
*fds[i] = std::move(result[i]);
}
return rc;
}
#endif
} // namespace base
} // namespace android
|
