base: add helpers for sending/receiving file descriptors.

Almost all of the uses of cmsg(3) in our source tree are wrong in at
least one of the following ways:

  - 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

Implement wrapper functions that implement this dumpster fire of an
API correctly.

Bug: http://b/122047630
Test: libbase_test32
Change-Id: I6ac34d67bbbf1bfa9727ab598248fc178ea19df9

1 files changed, 202 insertions, 0 deletions

diff --git a/base/cmsg_test.cpp b/base/cmsg_test.cpp
new file mode 100644
index 000000000..9ee5c8253
--- /dev/null
+++ b/base/cmsg_test.cpp
@@ -0,0 +1,202 @@
+/*
+ * 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.
+ */
+
+#include <android-base/cmsg.h>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/unique_fd.h>
+#include <gtest/gtest.h>
+
+#if !defined(_WIN32)
+
+using android::base::ReceiveFileDescriptors;
+using android::base::SendFileDescriptors;
+using android::base::unique_fd;
+
+static ino_t GetInode(int fd) {
+  struct stat st;
+  if (fstat(fd, &st) != 0) {
+    PLOG(FATAL) << "fstat failed";
+  }
+
+  return st.st_ino;
+}
+
+struct CmsgTest : ::testing::TestWithParam<bool> {
+  bool Seqpacket() { return GetParam(); }
+
+  void SetUp() override {
+    ASSERT_TRUE(
+        android::base::Socketpair(Seqpacket() ? SOCK_SEQPACKET : SOCK_STREAM, &send, &recv));
+    int dup1 = dup(tmp1.fd);
+    ASSERT_NE(-1, dup1);
+    int dup2 = dup(tmp2.fd);
+    ASSERT_NE(-1, dup2);
+
+    fd1.reset(dup1);
+    fd2.reset(dup2);
+
+    ino1 = GetInode(dup1);
+    ino2 = GetInode(dup2);
+  }
+
+  unique_fd send;
+  unique_fd recv;
+
+  TemporaryFile tmp1;
+  TemporaryFile tmp2;
+
+  unique_fd fd1;
+  unique_fd fd2;
+
+  ino_t ino1;
+  ino_t ino2;
+};
+
+TEST_P(CmsgTest, smoke) {
+  ASSERT_EQ(1, SendFileDescriptors(send.get(), "x", 1, fd1.get()));
+
+  char buf[2];
+  unique_fd received;
+  ASSERT_EQ(1, ReceiveFileDescriptors(recv.get(), buf, 2, &received));
+  ASSERT_EQ('x', buf[0]);
+  ASSERT_NE(-1, received.get());
+
+  ASSERT_EQ(ino1, GetInode(received.get()));
+}
+
+TEST_P(CmsgTest, msg_trunc) {
+  ASSERT_EQ(2, SendFileDescriptors(send.get(), "ab", 2, fd1.get(), fd2.get()));
+
+  char buf[2];
+  unique_fd received1, received2;
+
+  ssize_t rc = ReceiveFileDescriptors(recv.get(), buf, 1, &received1, &received2);
+  if (Seqpacket()) {
+    ASSERT_EQ(-1, rc);
+    ASSERT_EQ(EMSGSIZE, errno);
+    ASSERT_EQ(-1, received1.get());
+    ASSERT_EQ(-1, received2.get());
+  } else {
+    ASSERT_EQ(1, rc);
+    ASSERT_NE(-1, received1.get());
+    ASSERT_NE(-1, received2.get());
+    ASSERT_EQ(ino1, GetInode(received1.get()));
+    ASSERT_EQ(ino2, GetInode(received2.get()));
+    ASSERT_EQ(1, read(recv.get(), buf, 2));
+  }
+}
+
+TEST_P(CmsgTest, msg_ctrunc) {
+  ASSERT_EQ(1, SendFileDescriptors(send.get(), "a", 1, fd1.get(), fd2.get()));
+
+  char buf[2];
+  unique_fd received;
+  ASSERT_EQ(-1, ReceiveFileDescriptors(recv.get(), buf, 1, &received));
+  ASSERT_EQ(EMSGSIZE, errno);
+  ASSERT_EQ(-1, received.get());
+}
+
+TEST_P(CmsgTest, peek) {
+  ASSERT_EQ(1, SendFileDescriptors(send.get(), "a", 1, fd1.get()));
+
+  char buf[2];
+  ASSERT_EQ(1, ::recv(recv.get(), buf, sizeof(buf), MSG_PEEK));
+  ASSERT_EQ('a', buf[0]);
+
+  unique_fd received;
+  ASSERT_EQ(1, ReceiveFileDescriptors(recv.get(), buf, 1, &received));
+  ASSERT_EQ(ino1, GetInode(received.get()));
+}
+
+TEST_P(CmsgTest, stream_fd_association) {
+  if (Seqpacket()) {
+    return;
+  }
+
+  // fds are associated with the first byte of the write.
+  ASSERT_EQ(1, TEMP_FAILURE_RETRY(write(send.get(), "a", 1)));
+  ASSERT_EQ(2, SendFileDescriptors(send.get(), "bc", 2, fd1.get()));
+  ASSERT_EQ(1, SendFileDescriptors(send.get(), "d", 1, fd2.get()));
+  char buf[2];
+  ASSERT_EQ(2, TEMP_FAILURE_RETRY(read(recv.get(), buf, 2)));
+  ASSERT_EQ(0, memcmp(buf, "ab", 2));
+
+  std::vector<unique_fd> received1;
+  ssize_t rc = ReceiveFileDescriptorVector(recv.get(), buf, 1, 1, &received1);
+  ASSERT_EQ(1, rc);
+  ASSERT_EQ('c', buf[0]);
+  ASSERT_TRUE(received1.empty());
+
+  unique_fd received2;
+  rc = ReceiveFileDescriptors(recv.get(), buf, 1, &received2);
+  ASSERT_EQ(1, rc);
+  ASSERT_EQ('d', buf[0]);
+  ASSERT_EQ(ino2, GetInode(received2.get()));
+}
+
+TEST_P(CmsgTest, multiple_fd_ordering) {
+  ASSERT_EQ(1, SendFileDescriptors(send.get(), "a", 1, fd1.get(), fd2.get()));
+
+  char buf[2];
+  unique_fd received1, received2;
+  ASSERT_EQ(1, ReceiveFileDescriptors(recv.get(), buf, 1, &received1, &received2));
+
+  ASSERT_NE(-1, received1.get());
+  ASSERT_NE(-1, received2.get());
+
+  ASSERT_EQ(ino1, GetInode(received1.get()));
+  ASSERT_EQ(ino2, GetInode(received2.get()));
+}
+
+TEST_P(CmsgTest, separate_fd_ordering) {
+  ASSERT_EQ(1, SendFileDescriptors(send.get(), "a", 1, fd1.get()));
+  ASSERT_EQ(1, SendFileDescriptors(send.get(), "b", 1, fd2.get()));
+
+  char buf[2];
+  unique_fd received1, received2;
+  ASSERT_EQ(1, ReceiveFileDescriptors(recv.get(), buf, 1, &received1));
+  ASSERT_EQ(1, ReceiveFileDescriptors(recv.get(), buf, 1, &received2));
+
+  ASSERT_NE(-1, received1.get());
+  ASSERT_NE(-1, received2.get());
+
+  ASSERT_EQ(ino1, GetInode(received1.get()));
+  ASSERT_EQ(ino2, GetInode(received2.get()));
+}
+
+TEST_P(CmsgTest, separate_fds_no_coalescing) {
+  unique_fd sent1(dup(tmp1.fd));
+  unique_fd sent2(dup(tmp2.fd));
+
+  ASSERT_EQ(1, SendFileDescriptors(send.get(), "", 1, fd1.get()));
+  ASSERT_EQ(1, SendFileDescriptors(send.get(), "", 1, fd2.get()));
+
+  char buf[2];
+  std::vector<unique_fd> received;
+  ASSERT_EQ(1, ReceiveFileDescriptorVector(recv.get(), buf, 2, 2, &received));
+  ASSERT_EQ(1U, received.size());
+  ASSERT_EQ(ino1, GetInode(received[0].get()));
+
+  ASSERT_EQ(1, ReceiveFileDescriptorVector(recv.get(), buf, 2, 2, &received));
+  ASSERT_EQ(1U, received.size());
+  ASSERT_EQ(ino2, GetInode(received[0].get()));
+}
+
+INSTANTIATE_TEST_CASE_P(CmsgTest, CmsgTest, testing::Bool());
+
+#endif