Add support for the MSG_TRUNC msghdr flag.

The MSG_TRUNC flag is set in the msghdr when a message is truncated.

Fixes google/gvisor#200

PiperOrigin-RevId: 244440486
Change-Id: I03c7d5e7f5935c0c6b8d69b012db1780ac5b8456

3 files changed, 162 insertions, 0 deletions

diff --git a/test/syscalls/linux/socket_netlink_route.cc b/test/syscalls/linux/socket_netlink_route.cc
index 5f83836df..fa895d841 100644
--- a/test/syscalls/linux/socket_netlink_route.cc
+++ b/test/syscalls/linux/socket_netlink_route.cc
@@ -220,6 +220,86 @@ TEST(NetlinkRouteTest, GetLinkDump) {
   EXPECT_TRUE(loopbackFound);
 }
 
+TEST(NetlinkRouteTest, MsgHdrMsgTrunc) {
+  FileDescriptor fd = ASSERT_NO_ERRNO_AND_VALUE(NetlinkBoundSocket());
+
+  struct request {
+    struct nlmsghdr hdr;
+    struct ifinfomsg ifm;
+  };
+
+  constexpr uint32_t kSeq = 12345;
+
+  struct request req = {};
+  req.hdr.nlmsg_len = sizeof(req);
+  req.hdr.nlmsg_type = RTM_GETLINK;
+  req.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+  req.hdr.nlmsg_seq = kSeq;
+  req.ifm.ifi_family = AF_UNSPEC;
+
+  struct iovec iov = {};
+  iov.iov_base = &req;
+  iov.iov_len = sizeof(req);
+
+  struct msghdr msg = {};
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+  // No destination required; it defaults to pid 0, the kernel.
+
+  ASSERT_THAT(RetryEINTR(sendmsg)(fd.get(), &msg, 0), SyscallSucceeds());
+
+  // Small enough to ensure that the response doesn't fit.
+  constexpr size_t kBufferSize = 10;
+  std::vector<char> buf(kBufferSize);
+  iov.iov_base = buf.data();
+  iov.iov_len = buf.size();
+
+  ASSERT_THAT(RetryEINTR(recvmsg)(fd.get(), &msg, 0),
+              SyscallSucceedsWithValue(kBufferSize));
+  EXPECT_EQ((msg.msg_flags & MSG_TRUNC), MSG_TRUNC);
+}
+
+TEST(NetlinkRouteTest, MsgTruncMsgHdrMsgTrunc) {
+  FileDescriptor fd = ASSERT_NO_ERRNO_AND_VALUE(NetlinkBoundSocket());
+
+  struct request {
+    struct nlmsghdr hdr;
+    struct ifinfomsg ifm;
+  };
+
+  constexpr uint32_t kSeq = 12345;
+
+  struct request req = {};
+  req.hdr.nlmsg_len = sizeof(req);
+  req.hdr.nlmsg_type = RTM_GETLINK;
+  req.hdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
+  req.hdr.nlmsg_seq = kSeq;
+  req.ifm.ifi_family = AF_UNSPEC;
+
+  struct iovec iov = {};
+  iov.iov_base = &req;
+  iov.iov_len = sizeof(req);
+
+  struct msghdr msg = {};
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+  // No destination required; it defaults to pid 0, the kernel.
+
+  ASSERT_THAT(RetryEINTR(sendmsg)(fd.get(), &msg, 0), SyscallSucceeds());
+
+  // Small enough to ensure that the response doesn't fit.
+  constexpr size_t kBufferSize = 10;
+  std::vector<char> buf(kBufferSize);
+  iov.iov_base = buf.data();
+  iov.iov_len = buf.size();
+
+  int res = 0;
+  ASSERT_THAT(res = RetryEINTR(recvmsg)(fd.get(), &msg, MSG_TRUNC),
+              SyscallSucceeds());
+  EXPECT_GT(res, kBufferSize);
+  EXPECT_EQ((msg.msg_flags & MSG_TRUNC), MSG_TRUNC);
+}
+
 TEST(NetlinkRouteTest, ControlMessageIgnored) {
   FileDescriptor fd = ASSERT_NO_ERRNO_AND_VALUE(NetlinkBoundSocket());
   uint32_t port = ASSERT_NO_ERRNO_AND_VALUE(NetlinkPortID(fd.get()));
diff --git a/test/syscalls/linux/socket_non_stream.cc b/test/syscalls/linux/socket_non_stream.cc
index d49aab363..d170008a4 100644
--- a/test/syscalls/linux/socket_non_stream.cc
+++ b/test/syscalls/linux/socket_non_stream.cc
@@ -15,6 +15,7 @@
 #include "test/syscalls/linux/socket_non_stream.h"
 
 #include <stdio.h>
+#include <sys/socket.h>
 #include <sys/un.h>
 
 #include "gtest/gtest.h"
@@ -89,6 +90,33 @@ TEST_P(NonStreamSocketPairTest, SingleRecv) {
   EXPECT_EQ(0, memcmp(sent_data1, received_data, sizeof(sent_data1)));
 }
 
+TEST_P(NonStreamSocketPairTest, RecvmsgMsghdrFlagMsgTrunc) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  char sent_data[10];
+  RandomizeBuffer(sent_data, sizeof(sent_data));
+  ASSERT_THAT(
+      RetryEINTR(send)(sockets->first_fd(), sent_data, sizeof(sent_data), 0),
+      SyscallSucceedsWithValue(sizeof(sent_data)));
+
+  char received_data[sizeof(sent_data) / 2] = {};
+
+  struct iovec iov;
+  iov.iov_base = received_data;
+  iov.iov_len = sizeof(received_data);
+  struct msghdr msg = {};
+  msg.msg_flags = -1;
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+
+  ASSERT_THAT(RetryEINTR(recvmsg)(sockets->second_fd(), &msg, 0),
+              SyscallSucceedsWithValue(sizeof(received_data)));
+  EXPECT_EQ(0, memcmp(received_data, sent_data, sizeof(received_data)));
+
+  // Check that msghdr flags were updated.
+  EXPECT_EQ(msg.msg_flags, MSG_TRUNC);
+}
+
 // Stream sockets allow data sent with multiple sends to be peeked at in a
 // single recv. Datagram sockets (except for unix sockets) do not.
 //
@@ -142,6 +170,33 @@ TEST_P(NonStreamSocketPairTest, MsgTruncTruncation) {
                       sizeof(sent_data) / 2));
 }
 
+TEST_P(NonStreamSocketPairTest, MsgTruncTruncationRecvmsgMsghdrFlagMsgTrunc) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  char sent_data[10];
+  RandomizeBuffer(sent_data, sizeof(sent_data));
+  ASSERT_THAT(
+      RetryEINTR(send)(sockets->first_fd(), sent_data, sizeof(sent_data), 0),
+      SyscallSucceedsWithValue(sizeof(sent_data)));
+
+  char received_data[sizeof(sent_data) / 2] = {};
+
+  struct iovec iov;
+  iov.iov_base = received_data;
+  iov.iov_len = sizeof(received_data);
+  struct msghdr msg = {};
+  msg.msg_flags = -1;
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+
+  ASSERT_THAT(RetryEINTR(recvmsg)(sockets->second_fd(), &msg, MSG_TRUNC),
+              SyscallSucceedsWithValue(sizeof(sent_data)));
+  EXPECT_EQ(0, memcmp(received_data, sent_data, sizeof(received_data)));
+
+  // Check that msghdr flags were updated.
+  EXPECT_EQ(msg.msg_flags, MSG_TRUNC);
+}
+
 TEST_P(NonStreamSocketPairTest, MsgTruncSameSize) {
   auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
   char sent_data[512];
diff --git a/test/syscalls/linux/socket_stream.cc b/test/syscalls/linux/socket_stream.cc
index 32e9d958b..c8a8ad0f6 100644
--- a/test/syscalls/linux/socket_stream.cc
+++ b/test/syscalls/linux/socket_stream.cc
@@ -81,6 +81,33 @@ TEST_P(StreamSocketPairTest, WriteOneSideClosed) {
               SyscallFailsWithErrno(EPIPE));
 }
 
+TEST_P(StreamSocketPairTest, RecvmsgMsghdrFlagsNoMsgTrunc) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  char sent_data[10];
+  RandomizeBuffer(sent_data, sizeof(sent_data));
+  ASSERT_THAT(
+      RetryEINTR(send)(sockets->first_fd(), sent_data, sizeof(sent_data), 0),
+      SyscallSucceedsWithValue(sizeof(sent_data)));
+
+  char received_data[sizeof(sent_data) / 2] = {};
+
+  struct iovec iov;
+  iov.iov_base = received_data;
+  iov.iov_len = sizeof(received_data);
+  struct msghdr msg = {};
+  msg.msg_flags = -1;
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+
+  ASSERT_THAT(RetryEINTR(recvmsg)(sockets->second_fd(), &msg, 0),
+              SyscallSucceedsWithValue(sizeof(received_data)));
+  EXPECT_EQ(0, memcmp(received_data, sent_data, sizeof(received_data)));
+
+  // Check that msghdr flags were cleared (MSG_TRUNC was not set).
+  EXPECT_EQ(msg.msg_flags, 0);
+}
+
 TEST_P(StreamSocketPairTest, MsgTrunc) {
   auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
   char sent_data[512];