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 #include <android-base/cmsg.h>
18
19 #include <errno.h>
20 #include <fcntl.h>
21 #include <stdlib.h>
22 #include <sys/socket.h>
23 #include <sys/user.h>
24
25 #include <memory>
26
27 #include <android-base/logging.h>
28
29 namespace android {
30 namespace base {
31
SendFileDescriptorVector(int sockfd,const void * data,size_t len,const std::vector<int> & fds)32 ssize_t SendFileDescriptorVector(int sockfd, const void* data, size_t len,
33 const std::vector<int>& fds) {
34 size_t cmsg_space = CMSG_SPACE(sizeof(int) * fds.size());
35 size_t cmsg_len = CMSG_LEN(sizeof(int) * fds.size());
36 if (cmsg_space >= PAGE_SIZE) {
37 errno = ENOMEM;
38 return -1;
39 }
40
41 alignas(struct cmsghdr) char cmsg_buf[cmsg_space];
42 iovec iov = {.iov_base = const_cast<void*>(data), .iov_len = len};
43 msghdr msg = {
44 .msg_name = nullptr,
45 .msg_namelen = 0,
46 .msg_iov = &iov,
47 .msg_iovlen = 1,
48 .msg_control = cmsg_buf,
49 // We can't cast to the actual type of the field, because it's different across platforms.
50 .msg_controllen = static_cast<unsigned int>(cmsg_space),
51 .msg_flags = 0,
52 };
53
54 struct cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
55 cmsg->cmsg_level = SOL_SOCKET;
56 cmsg->cmsg_type = SCM_RIGHTS;
57 cmsg->cmsg_len = cmsg_len;
58
59 int* cmsg_fds = reinterpret_cast<int*>(CMSG_DATA(cmsg));
60 for (size_t i = 0; i < fds.size(); ++i) {
61 cmsg_fds[i] = fds[i];
62 }
63
64 #if defined(__linux__)
65 int flags = MSG_NOSIGNAL;
66 #else
67 int flags = 0;
68 #endif
69
70 return TEMP_FAILURE_RETRY(sendmsg(sockfd, &msg, flags));
71 }
72
ReceiveFileDescriptorVector(int sockfd,void * data,size_t len,size_t max_fds,std::vector<unique_fd> * fds)73 ssize_t ReceiveFileDescriptorVector(int sockfd, void* data, size_t len, size_t max_fds,
74 std::vector<unique_fd>* fds) {
75 fds->clear();
76
77 size_t cmsg_space = CMSG_SPACE(sizeof(int) * max_fds);
78 if (cmsg_space >= PAGE_SIZE) {
79 errno = ENOMEM;
80 return -1;
81 }
82
83 alignas(struct cmsghdr) char cmsg_buf[cmsg_space];
84 iovec iov = {.iov_base = const_cast<void*>(data), .iov_len = len};
85 msghdr msg = {
86 .msg_name = nullptr,
87 .msg_namelen = 0,
88 .msg_iov = &iov,
89 .msg_iovlen = 1,
90 .msg_control = cmsg_buf,
91 // We can't cast to the actual type of the field, because it's different across platforms.
92 .msg_controllen = static_cast<unsigned int>(cmsg_space),
93 .msg_flags = 0,
94 };
95
96 int flags = MSG_TRUNC | MSG_CTRUNC;
97 #if defined(__linux__)
98 flags |= MSG_CMSG_CLOEXEC | MSG_NOSIGNAL;
99 #endif
100
101 ssize_t rc = TEMP_FAILURE_RETRY(recvmsg(sockfd, &msg, flags));
102
103 if (rc == -1) {
104 return -1;
105 }
106
107 int error = 0;
108 if ((msg.msg_flags & MSG_TRUNC)) {
109 LOG(ERROR) << "message was truncated when receiving file descriptors";
110 error = EMSGSIZE;
111 } else if ((msg.msg_flags & MSG_CTRUNC)) {
112 LOG(ERROR) << "control message was truncated when receiving file descriptors";
113 error = EMSGSIZE;
114 }
115
116 std::vector<unique_fd> received_fds;
117 struct cmsghdr* cmsg;
118 for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != nullptr; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
119 if (cmsg->cmsg_level != SOL_SOCKET || cmsg->cmsg_type != SCM_RIGHTS) {
120 LOG(ERROR) << "received unexpected cmsg: [" << cmsg->cmsg_level << ", " << cmsg->cmsg_type
121 << "]";
122 error = EBADMSG;
123 continue;
124 }
125
126 // There isn't a macro that does the inverse of CMSG_LEN, so hack around it ourselves, with
127 // some asserts to ensure that CMSG_LEN behaves as we expect.
128 #if defined(__linux__)
129 #define CMSG_ASSERT static_assert
130 #else
131 // CMSG_LEN is somehow not constexpr on darwin.
132 #define CMSG_ASSERT CHECK
133 #endif
134 CMSG_ASSERT(CMSG_LEN(0) + 1 * sizeof(int) == CMSG_LEN(1 * sizeof(int)));
135 CMSG_ASSERT(CMSG_LEN(0) + 2 * sizeof(int) == CMSG_LEN(2 * sizeof(int)));
136 CMSG_ASSERT(CMSG_LEN(0) + 3 * sizeof(int) == CMSG_LEN(3 * sizeof(int)));
137 CMSG_ASSERT(CMSG_LEN(0) + 4 * sizeof(int) == CMSG_LEN(4 * sizeof(int)));
138
139 if (cmsg->cmsg_len % sizeof(int) != 0) {
140 LOG(FATAL) << "cmsg_len(" << cmsg->cmsg_len << ") not aligned to sizeof(int)";
141 } else if (cmsg->cmsg_len <= CMSG_LEN(0)) {
142 LOG(FATAL) << "cmsg_len(" << cmsg->cmsg_len << ") not long enough to hold any data";
143 }
144
145 int* cmsg_fds = reinterpret_cast<int*>(CMSG_DATA(cmsg));
146 size_t cmsg_fdcount = static_cast<size_t>(cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
147 for (size_t i = 0; i < cmsg_fdcount; ++i) {
148 #if !defined(__linux__)
149 // Linux uses MSG_CMSG_CLOEXEC instead of doing this manually.
150 fcntl(cmsg_fds[i], F_SETFD, FD_CLOEXEC);
151 #endif
152 received_fds.emplace_back(cmsg_fds[i]);
153 }
154 }
155
156 if (error != 0) {
157 errno = error;
158 return -1;
159 }
160
161 if (received_fds.size() > max_fds) {
162 LOG(ERROR) << "received too many file descriptors, expected " << fds->size() << ", received "
163 << received_fds.size();
164 errno = EMSGSIZE;
165 return -1;
166 }
167
168 *fds = std::move(received_fds);
169 return rc;
170 }
171
172 } // namespace base
173 } // namespace android
174