Stub support for TCP_SYNCNT and TCP_WINDOW_CLAMP.

This change adds support for TCP_SYNCNT and TCP_WINDOW_CLAMP options
in GetSockOpt/SetSockOpt. This change does not really change any
behaviour in Netstack and only stores/returns the stored value.

Actual honoring of these options will be added as required.

Fixes #2626, #2625

PiperOrigin-RevId: 311453777

2 files changed, 228 insertions, 2 deletions

diff --git a/test/syscalls/linux/socket_ip_tcp_generic.cc b/test/syscalls/linux/socket_ip_tcp_generic.cc
index 27779e47c..fa81845fd 100644
--- a/test/syscalls/linux/socket_ip_tcp_generic.cc
+++ b/test/syscalls/linux/socket_ip_tcp_generic.cc
@@ -876,6 +876,51 @@ TEST_P(TCPSocketPairTest, SetTCPUserTimeoutAboveZero) {
   EXPECT_EQ(get, kAbove);
 }
 
+TEST_P(TCPSocketPairTest, SetTCPWindowClampBelowMinRcvBufConnectedSocket) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+  // Discover minimum receive buf by setting a really low value
+  // for the receive buffer.
+  constexpr int kZero = 0;
+  EXPECT_THAT(setsockopt(sockets->first_fd(), SOL_SOCKET, SO_RCVBUF, &kZero,
+                         sizeof(kZero)),
+              SyscallSucceeds());
+
+  // Now retrieve the minimum value for SO_RCVBUF as the set above should
+  // have caused SO_RCVBUF for the socket to be set to the minimum.
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  ASSERT_THAT(
+      getsockopt(sockets->first_fd(), SOL_SOCKET, SO_RCVBUF, &get, &get_len),
+      SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  int min_so_rcvbuf = get;
+
+  {
+    // Setting TCP_WINDOW_CLAMP to zero for a connected socket is not permitted.
+    constexpr int kZero = 0;
+    EXPECT_THAT(setsockopt(sockets->first_fd(), IPPROTO_TCP, TCP_WINDOW_CLAMP,
+                           &kZero, sizeof(kZero)),
+                SyscallFailsWithErrno(EINVAL));
+
+    // Non-zero clamp values below MIN_SO_RCVBUF/2 should result in the clamp
+    // being set to MIN_SO_RCVBUF/2.
+    int below_half_min_so_rcvbuf = min_so_rcvbuf / 2 - 1;
+    EXPECT_THAT(
+        setsockopt(sockets->first_fd(), IPPROTO_TCP, TCP_WINDOW_CLAMP,
+                   &below_half_min_so_rcvbuf, sizeof(below_half_min_so_rcvbuf)),
+        SyscallSucceeds());
+
+    int get = -1;
+    socklen_t get_len = sizeof(get);
+
+    ASSERT_THAT(getsockopt(sockets->first_fd(), IPPROTO_TCP, TCP_WINDOW_CLAMP,
+                           &get, &get_len),
+                SyscallSucceedsWithValue(0));
+    EXPECT_EQ(get_len, sizeof(get));
+    EXPECT_EQ(min_so_rcvbuf / 2, get);
+  }
+}
+
 TEST_P(TCPSocketPairTest, TCPResetDuringClose_NoRandomSave) {
   DisableSave ds;  // Too many syscalls.
   constexpr int kThreadCount = 1000;
diff --git a/test/syscalls/linux/tcp_socket.cc b/test/syscalls/linux/tcp_socket.cc
index d9c1ac0e1..a4d2953e1 100644
--- a/test/syscalls/linux/tcp_socket.cc
+++ b/test/syscalls/linux/tcp_socket.cc
@@ -1313,7 +1313,7 @@ TEST_P(SimpleTcpSocketTest, SetTCPDeferAcceptNeg) {
   int get = -1;
   socklen_t get_len = sizeof(get);
   ASSERT_THAT(
-      getsockopt(s.get(), IPPROTO_TCP, TCP_USER_TIMEOUT, &get, &get_len),
+      getsockopt(s.get(), IPPROTO_TCP, TCP_DEFER_ACCEPT, &get, &get_len),
       SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_len, sizeof(get));
   EXPECT_EQ(get, 0);
@@ -1326,7 +1326,7 @@ TEST_P(SimpleTcpSocketTest, GetTCPDeferAcceptDefault) {
   int get = -1;
   socklen_t get_len = sizeof(get);
   ASSERT_THAT(
-      getsockopt(s.get(), IPPROTO_TCP, TCP_USER_TIMEOUT, &get, &get_len),
+      getsockopt(s.get(), IPPROTO_TCP, TCP_DEFER_ACCEPT, &get, &get_len),
       SyscallSucceedsWithValue(0));
   EXPECT_EQ(get_len, sizeof(get));
   EXPECT_EQ(get, 0);
@@ -1378,6 +1378,187 @@ TEST_P(SimpleTcpSocketTest, TCPConnectSoRcvBufRace) {
       SyscallSucceedsWithValue(0));
 }
 
+TEST_P(SimpleTcpSocketTest, SetTCPSynCntLessThanOne) {
+  FileDescriptor s =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(GetParam(), SOCK_STREAM, IPPROTO_TCP));
+
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  ASSERT_THAT(getsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &get, &get_len),
+              SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  int default_syn_cnt = get;
+
+  {
+    // TCP_SYNCNT less than 1 should be rejected with an EINVAL.
+    constexpr int kZero = 0;
+    EXPECT_THAT(
+        setsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &kZero, sizeof(kZero)),
+        SyscallFailsWithErrno(EINVAL));
+
+    // TCP_SYNCNT less than 1 should be rejected with an EINVAL.
+    constexpr int kNeg = -1;
+    EXPECT_THAT(
+        setsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &kNeg, sizeof(kNeg)),
+        SyscallFailsWithErrno(EINVAL));
+
+    int get = -1;
+    socklen_t get_len = sizeof(get);
+
+    ASSERT_THAT(getsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &get, &get_len),
+                SyscallSucceedsWithValue(0));
+    EXPECT_EQ(get_len, sizeof(get));
+    EXPECT_EQ(default_syn_cnt, get);
+  }
+}
+
+TEST_P(SimpleTcpSocketTest, GetTCPSynCntDefault) {
+  FileDescriptor s =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(GetParam(), SOCK_STREAM, IPPROTO_TCP));
+
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  constexpr int kDefaultSynCnt = 6;
+
+  ASSERT_THAT(getsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &get, &get_len),
+              SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  EXPECT_EQ(get, kDefaultSynCnt);
+}
+
+TEST_P(SimpleTcpSocketTest, SetTCPSynCntGreaterThanOne) {
+  FileDescriptor s =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(GetParam(), SOCK_STREAM, IPPROTO_TCP));
+  constexpr int kTCPSynCnt = 20;
+  ASSERT_THAT(setsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &kTCPSynCnt,
+                         sizeof(kTCPSynCnt)),
+              SyscallSucceeds());
+
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  ASSERT_THAT(getsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &get, &get_len),
+              SyscallSucceeds());
+  EXPECT_EQ(get_len, sizeof(get));
+  EXPECT_EQ(get, kTCPSynCnt);
+}
+
+TEST_P(SimpleTcpSocketTest, SetTCPSynCntAboveMax) {
+  FileDescriptor s =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(GetParam(), SOCK_STREAM, IPPROTO_TCP));
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  ASSERT_THAT(getsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &get, &get_len),
+              SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  int default_syn_cnt = get;
+  {
+    constexpr int kTCPSynCnt = 256;
+    ASSERT_THAT(setsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &kTCPSynCnt,
+                           sizeof(kTCPSynCnt)),
+                SyscallFailsWithErrno(EINVAL));
+
+    int get = -1;
+    socklen_t get_len = sizeof(get);
+    ASSERT_THAT(getsockopt(s.get(), IPPROTO_TCP, TCP_SYNCNT, &get, &get_len),
+                SyscallSucceeds());
+    EXPECT_EQ(get_len, sizeof(get));
+    EXPECT_EQ(get, default_syn_cnt);
+  }
+}
+
+TEST_P(SimpleTcpSocketTest, SetTCPWindowClampBelowMinRcvBuf) {
+  FileDescriptor s =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(GetParam(), SOCK_STREAM, IPPROTO_TCP));
+
+  // Discover minimum receive buf by setting a really low value
+  // for the receive buffer.
+  constexpr int kZero = 0;
+  EXPECT_THAT(setsockopt(s.get(), SOL_SOCKET, SO_RCVBUF, &kZero, sizeof(kZero)),
+              SyscallSucceeds());
+
+  // Now retrieve the minimum value for SO_RCVBUF as the set above should
+  // have caused SO_RCVBUF for the socket to be set to the minimum.
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  ASSERT_THAT(getsockopt(s.get(), SOL_SOCKET, SO_RCVBUF, &get, &get_len),
+              SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  int min_so_rcvbuf = get;
+
+  {
+    // TCP_WINDOW_CLAMP less than min_so_rcvbuf/2 should be set to
+    // min_so_rcvbuf/2.
+    int below_half_min_rcvbuf = min_so_rcvbuf / 2 - 1;
+    EXPECT_THAT(
+        setsockopt(s.get(), IPPROTO_TCP, TCP_WINDOW_CLAMP,
+                   &below_half_min_rcvbuf, sizeof(below_half_min_rcvbuf)),
+        SyscallSucceeds());
+
+    int get = -1;
+    socklen_t get_len = sizeof(get);
+
+    ASSERT_THAT(
+        getsockopt(s.get(), IPPROTO_TCP, TCP_WINDOW_CLAMP, &get, &get_len),
+        SyscallSucceedsWithValue(0));
+    EXPECT_EQ(get_len, sizeof(get));
+    EXPECT_EQ(min_so_rcvbuf / 2, get);
+  }
+}
+
+TEST_P(SimpleTcpSocketTest, SetTCPWindowClampZeroClosedSocket) {
+  FileDescriptor s =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(GetParam(), SOCK_STREAM, IPPROTO_TCP));
+  constexpr int kZero = 0;
+  ASSERT_THAT(
+      setsockopt(s.get(), IPPROTO_TCP, TCP_WINDOW_CLAMP, &kZero, sizeof(kZero)),
+      SyscallSucceeds());
+
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  ASSERT_THAT(
+      getsockopt(s.get(), IPPROTO_TCP, TCP_WINDOW_CLAMP, &get, &get_len),
+      SyscallSucceeds());
+  EXPECT_EQ(get_len, sizeof(get));
+  EXPECT_EQ(get, kZero);
+}
+
+TEST_P(SimpleTcpSocketTest, SetTCPWindowClampAboveHalfMinRcvBuf) {
+  FileDescriptor s =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(GetParam(), SOCK_STREAM, IPPROTO_TCP));
+
+  // Discover minimum receive buf by setting a really low value
+  // for the receive buffer.
+  constexpr int kZero = 0;
+  EXPECT_THAT(setsockopt(s.get(), SOL_SOCKET, SO_RCVBUF, &kZero, sizeof(kZero)),
+              SyscallSucceeds());
+
+  // Now retrieve the minimum value for SO_RCVBUF as the set above should
+  // have caused SO_RCVBUF for the socket to be set to the minimum.
+  int get = -1;
+  socklen_t get_len = sizeof(get);
+  ASSERT_THAT(getsockopt(s.get(), SOL_SOCKET, SO_RCVBUF, &get, &get_len),
+              SyscallSucceedsWithValue(0));
+  EXPECT_EQ(get_len, sizeof(get));
+  int min_so_rcvbuf = get;
+
+  {
+    int above_half_min_rcv_buf = min_so_rcvbuf / 2 + 1;
+    EXPECT_THAT(
+        setsockopt(s.get(), IPPROTO_TCP, TCP_WINDOW_CLAMP,
+                   &above_half_min_rcv_buf, sizeof(above_half_min_rcv_buf)),
+        SyscallSucceeds());
+
+    int get = -1;
+    socklen_t get_len = sizeof(get);
+
+    ASSERT_THAT(
+        getsockopt(s.get(), IPPROTO_TCP, TCP_WINDOW_CLAMP, &get, &get_len),
+        SyscallSucceedsWithValue(0));
+    EXPECT_EQ(get_len, sizeof(get));
+    EXPECT_EQ(above_half_min_rcv_buf, get);
+  }
+}
+
 INSTANTIATE_TEST_SUITE_P(AllInetTests, SimpleTcpSocketTest,
                          ::testing::Values(AF_INET, AF_INET6));