gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/test/syscalls/linux/select.cc

// Copyright 2018 The gVisor Authors.
//
// 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 <fcntl.h>
#include <sys/resource.h>
#include <sys/select.h>
#include <sys/time.h>

#include <climits>
#include <csignal>
#include <cstdio>

#include "gtest/gtest.h"
#include "absl/time/time.h"
#include "test/syscalls/linux/base_poll_test.h"
#include "test/util/file_descriptor.h"
#include "test/util/multiprocess_util.h"
#include "test/util/posix_error.h"
#include "test/util/rlimit_util.h"
#include "test/util/temp_path.h"
#include "test/util/test_util.h"

namespace gvisor {
namespace testing {
namespace {

class SelectTest : public BasePollTest {
 protected:
  void SetUp() override { BasePollTest::SetUp(); }
  void TearDown() override { BasePollTest::TearDown(); }
};

// See that when there are no FD sets, select behaves like sleep.
TEST_F(SelectTest, NullFds) {
  struct timeval timeout = absl::ToTimeval(absl::Milliseconds(10));
  ASSERT_THAT(select(0, nullptr, nullptr, nullptr, &timeout),
              SyscallSucceeds());
  EXPECT_EQ(timeout.tv_sec, 0);
  EXPECT_EQ(timeout.tv_usec, 0);

  timeout = absl::ToTimeval(absl::Milliseconds(10));
  ASSERT_THAT(select(1, nullptr, nullptr, nullptr, &timeout),
              SyscallSucceeds());
  EXPECT_EQ(timeout.tv_sec, 0);
  EXPECT_EQ(timeout.tv_usec, 0);
}

TEST_F(SelectTest, NegativeNfds) {
  EXPECT_THAT(select(-1, nullptr, nullptr, nullptr, nullptr),
              SyscallFailsWithErrno(EINVAL));
  EXPECT_THAT(select(-100000, nullptr, nullptr, nullptr, nullptr),
              SyscallFailsWithErrno(EINVAL));
  EXPECT_THAT(select(INT_MIN, nullptr, nullptr, nullptr, nullptr),
              SyscallFailsWithErrno(EINVAL));
}

TEST_F(SelectTest, ClosedFds) {
  auto temp_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
  FileDescriptor fd =
      ASSERT_NO_ERRNO_AND_VALUE(Open(temp_file.path(), O_RDONLY));

  // We can't rely on a file descriptor being closed in a multi threaded
  // application so fork to get a clean process.
  EXPECT_THAT(InForkedProcess([&] {
                int fd_num = fd.get();
                fd.reset();

                fd_set read_set;
                FD_ZERO(&read_set);
                FD_SET(fd_num, &read_set);

                struct timeval timeout =
                    absl::ToTimeval(absl::Milliseconds(10));
                TEST_PCHECK(select(fd_num + 1, &read_set, nullptr, nullptr,
                                   &timeout) != 0);
                TEST_PCHECK(errno == EBADF);
              }),
              IsPosixErrorOkAndHolds(0));
}

TEST_F(SelectTest, ZeroTimeout) {
  struct timeval timeout = {};
  EXPECT_THAT(select(1, nullptr, nullptr, nullptr, &timeout),
              SyscallSucceeds());
  // Ignore timeout as its value is now undefined.
}

// If random S/R interrupts the select, SIGALRM may be delivered before select
// restarts, causing the select to hang forever.
TEST_F(SelectTest, NoTimeout) {
  // When there's no timeout, select may never return so set a timer.
  SetTimer(absl::Milliseconds(100));
  // See that we get interrupted by the timer.
  ASSERT_THAT(select(1, nullptr, nullptr, nullptr, nullptr),
              SyscallFailsWithErrno(EINTR));
  EXPECT_TRUE(TimerFired());
}

TEST_F(SelectTest, InvalidTimeoutNegative) {
  struct timeval timeout = absl::ToTimeval(absl::Microseconds(-1));
  EXPECT_THAT(select(1, nullptr, nullptr, nullptr, &timeout),
              SyscallFailsWithErrno(EINVAL));
  // Ignore timeout as its value is now undefined.
}

// Verify that a signal interrupts select.
//
// If random S/R interrupts the select, SIGALRM may be delivered before select
// restarts, causing the select to hang forever.
TEST_F(SelectTest, InterruptedBySignal) {
  absl::Duration duration(absl::Seconds(5));
  struct timeval timeout = absl::ToTimeval(duration);
  SetTimer(absl::Milliseconds(100));
  ASSERT_FALSE(TimerFired());
  ASSERT_THAT(select(1, nullptr, nullptr, nullptr, &timeout),
              SyscallFailsWithErrno(EINTR));
  EXPECT_TRUE(TimerFired());
  // Ignore timeout as its value is now undefined.
}

TEST_F(SelectTest, IgnoreBitsAboveNfds) {
  // fd_set is a bit array with at least FD_SETSIZE bits. Test that bits
  // corresponding to file descriptors above nfds are ignored.
  fd_set read_set;
  FD_ZERO(&read_set);
  constexpr int kNfds = 1;
  for (int fd = kNfds; fd < FD_SETSIZE; fd++) {
    FD_SET(fd, &read_set);
  }
  // Pass a zero timeout so that select returns immediately.
  struct timeval timeout = {};
  EXPECT_THAT(select(kNfds, &read_set, nullptr, nullptr, &timeout),
              SyscallSucceedsWithValue(0));
}

// This test illustrates Linux's behavior of 'select' calls passing after
// setrlimit RLIMIT_NOFILE is called. In particular, versions of sshd rely on
// this behavior. See b/122318458.
TEST_F(SelectTest, SetrlimitCallNOFILE) {
  fd_set read_set;
  FD_ZERO(&read_set);
  timeval timeout = {};
  const FileDescriptor fd = ASSERT_NO_ERRNO_AND_VALUE(
      Open(NewTempAbsPath(), O_RDONLY | O_CREAT, S_IRUSR));

  Cleanup reset_rlimit =
      ASSERT_NO_ERRNO_AND_VALUE(ScopedSetSoftRlimit(RLIMIT_NOFILE, 0));

  FD_SET(fd.get(), &read_set);
  // this call with zero timeout should return immediately
  EXPECT_THAT(select(fd.get() + 1, &read_set, nullptr, nullptr, &timeout),
              SyscallSucceeds());
}

}  // namespace
}  // namespace testing
}  // namespace gvisor