1 files changed, 288 insertions, 0 deletions
diff --git a/test/syscalls/linux/symlink.cc b/test/syscalls/linux/symlink.cc
new file mode 100644
index 000000000..cfc87bc8f
--- /dev/null
+++ b/test/syscalls/linux/symlink.cc
@@ -0,0 +1,288 @@
+// Copyright 2018 Google LLC
+//
+// 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 <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <string>
+
+#include "gtest/gtest.h"
+#include "test/util/capability_util.h"
+#include "test/util/file_descriptor.h"
+#include "test/util/fs_util.h"
+#include "test/util/temp_path.h"
+#include "test/util/test_util.h"
+
+namespace gvisor {
+namespace testing {
+
+namespace {
+
+mode_t FilePermission(const std::string& path) {
+  struct stat buf = {0};
+  TEST_CHECK(lstat(path.c_str(), &buf) == 0);
+  return buf.st_mode & 0777;
+}
+
+// Test that name collisions are checked on the new link path, not the source
+// path.
+TEST(SymlinkTest, CanCreateSymlinkWithCachedSourceDirent) {
+  const std::string srcname = NewTempAbsPath();
+  const std::string newname = NewTempAbsPath();
+  const std::string basedir = std::string(Dirname(srcname));
+  ASSERT_EQ(basedir, Dirname(newname));
+
+  ASSERT_THAT(chdir(basedir.c_str()), SyscallSucceeds());
+
+  // Open the source node to cause the underlying dirent to be cached. It will
+  // remain cached while we have the file open.
+  int fd;
+  ASSERT_THAT(fd = open(srcname.c_str(), O_CREAT | O_RDWR, 0666),
+              SyscallSucceeds());
+  FileDescriptor fd_closer(fd);
+
+  // Attempt to create a symlink. If the bug exists, this will fail since the
+  // dirent link creation code will check for a name collision on the source
+  // link name.
+  EXPECT_THAT(symlink(std::string(Basename(srcname)).c_str(),
+                      std::string(Basename(newname)).c_str()),
+              SyscallSucceeds());
+}
+
+TEST(SymlinkTest, CanCreateSymlinkFile) {
+  const std::string oldname = NewTempAbsPath();
+  const std::string newname = NewTempAbsPath();
+
+  int fd;
+  ASSERT_THAT(fd = open(oldname.c_str(), O_CREAT | O_RDWR, 0666),
+              SyscallSucceeds());
+  EXPECT_THAT(close(fd), SyscallSucceeds());
+
+  EXPECT_THAT(symlink(oldname.c_str(), newname.c_str()), SyscallSucceeds());
+  EXPECT_EQ(FilePermission(newname), 0777);
+
+  auto link = ASSERT_NO_ERRNO_AND_VALUE(ReadLink(newname));
+  EXPECT_EQ(oldname, link);
+
+  EXPECT_THAT(unlink(newname.c_str()), SyscallSucceeds());
+  EXPECT_THAT(unlink(oldname.c_str()), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, CanCreateSymlinkDir) {
+  const std::string olddir = NewTempAbsPath();
+  const std::string newdir = NewTempAbsPath();
+
+  EXPECT_THAT(mkdir(olddir.c_str(), 0777), SyscallSucceeds());
+  EXPECT_THAT(symlink(olddir.c_str(), newdir.c_str()), SyscallSucceeds());
+  EXPECT_EQ(FilePermission(newdir), 0777);
+
+  auto link = ASSERT_NO_ERRNO_AND_VALUE(ReadLink(newdir));
+  EXPECT_EQ(olddir, link);
+
+  EXPECT_THAT(unlink(newdir.c_str()), SyscallSucceeds());
+
+  ASSERT_THAT(rmdir(olddir.c_str()), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, CannotCreateSymlinkInReadOnlyDir) {
+  // Drop capabilities that allow us to override file and directory permissions.
+  ASSERT_NO_ERRNO(SetCapability(CAP_DAC_OVERRIDE, false));
+  ASSERT_NO_ERRNO(SetCapability(CAP_DAC_READ_SEARCH, false));
+
+  const std::string olddir = NewTempAbsPath();
+  ASSERT_THAT(mkdir(olddir.c_str(), 0444), SyscallSucceeds());
+
+  const std::string newdir = NewTempAbsPathInDir(olddir);
+  EXPECT_THAT(symlink(olddir.c_str(), newdir.c_str()),
+              SyscallFailsWithErrno(EACCES));
+
+  ASSERT_THAT(rmdir(olddir.c_str()), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, CannotSymlinkOverExistingFile) {
+  const std::string oldname = NewTempAbsPath();
+  const std::string newname = NewTempAbsPath();
+
+  int oldfd;
+  int newfd;
+  ASSERT_THAT(oldfd = open(oldname.c_str(), O_CREAT | O_RDWR, 0666),
+              SyscallSucceeds());
+  EXPECT_THAT(close(oldfd), SyscallSucceeds());
+  ASSERT_THAT(newfd = open(newname.c_str(), O_CREAT | O_RDWR, 0666),
+              SyscallSucceeds());
+  EXPECT_THAT(close(newfd), SyscallSucceeds());
+
+  EXPECT_THAT(symlink(oldname.c_str(), newname.c_str()),
+              SyscallFailsWithErrno(EEXIST));
+
+  EXPECT_THAT(unlink(oldname.c_str()), SyscallSucceeds());
+  EXPECT_THAT(unlink(newname.c_str()), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, OldnameIsEmpty) {
+  const std::string newname = NewTempAbsPath();
+  EXPECT_THAT(symlink("", newname.c_str()), SyscallFailsWithErrno(ENOENT));
+}
+
+TEST(SymlinkTest, OldnameIsDangling) {
+  const std::string newname = NewTempAbsPath();
+  EXPECT_THAT(symlink("/dangling", newname.c_str()), SyscallSucceeds());
+
+  // This is required for S/R random save tests, which pre-run this test
+  // in the same TEST_TMPDIR, which means that we need to clean it for any
+  // operations exclusively creating files, like symlink above.
+  EXPECT_THAT(unlink(newname.c_str()), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, NewnameCannotExist) {
+  const std::string newname =
+      JoinPath(GetAbsoluteTestTmpdir(), "thisdoesnotexist", "foo");
+  EXPECT_THAT(symlink("/thisdoesnotmatter", newname.c_str()),
+              SyscallFailsWithErrno(ENOENT));
+}
+
+TEST(SymlinkTest, CanEvaluateLink) {
+  const std::string oldname = NewTempAbsPath();
+  const std::string newname = NewTempAbsPath();
+
+  int fd;
+  ASSERT_THAT(fd = open(oldname.c_str(), O_CREAT | O_RDWR, 0666),
+              SyscallSucceeds());
+  struct stat old;
+  EXPECT_THAT(fstat(fd, &old), SyscallSucceeds());
+  EXPECT_THAT(close(fd), SyscallSucceeds());
+
+  EXPECT_THAT(symlink(oldname.c_str(), newname.c_str()), SyscallSucceeds());
+  EXPECT_EQ(FilePermission(newname), 0777);
+
+  EXPECT_THAT(fd = open(newname.c_str(), O_RDWR, 0666), SyscallSucceeds());
+  struct stat old_linked;
+  EXPECT_THAT(fstat(fd, &old_linked), SyscallSucceeds());
+  EXPECT_THAT(close(fd), SyscallSucceeds());
+
+  // Check that in fact newname points to the file we expect.
+  // FIXME: use only inodes here once they are consistent,
+  // but this is better than nothing.
+  EXPECT_EQ(old.st_dev, old_linked.st_dev);
+  EXPECT_EQ(old.st_mode, old_linked.st_mode);
+  EXPECT_EQ(old.st_size, old_linked.st_size);
+
+  EXPECT_THAT(unlink(newname.c_str()), SyscallSucceeds());
+  EXPECT_THAT(unlink(oldname.c_str()), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, TargetIsNotMapped) {
+  const std::string oldname = NewTempAbsPath();
+  const std::string newname = NewTempAbsPath();
+
+  int fd;
+  // Create the target so that when we read the link, it exists.
+  ASSERT_THAT(fd = open(oldname.c_str(), O_CREAT | O_RDWR, 0666),
+              SyscallSucceeds());
+  EXPECT_THAT(close(fd), SyscallSucceeds());
+
+  // Create a symlink called newname that points to oldname.
+  EXPECT_THAT(symlink(oldname.c_str(), newname.c_str()), SyscallSucceeds());
+
+  std::vector<char> buf(1024);
+  int linksize;
+  // Read the link and assert that the oldname is still the same.
+  EXPECT_THAT(linksize = readlink(newname.c_str(), buf.data(), 1024),
+              SyscallSucceeds());
+  EXPECT_EQ(0, strncmp(oldname.c_str(), buf.data(), linksize));
+
+  EXPECT_THAT(unlink(newname.c_str()), SyscallSucceeds());
+  EXPECT_THAT(unlink(oldname.c_str()), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, PreadFromSymlink) {
+  std::string name = NewTempAbsPath();
+  int fd;
+  ASSERT_THAT(fd = open(name.c_str(), O_CREAT, 0644), SyscallSucceeds());
+  ASSERT_THAT(close(fd), SyscallSucceeds());
+
+  std::string linkname = NewTempAbsPath();
+  ASSERT_THAT(symlink(name.c_str(), linkname.c_str()), SyscallSucceeds());
+
+  ASSERT_THAT(fd = open(linkname.c_str(), O_RDONLY), SyscallSucceeds());
+
+  char buf[1024];
+  EXPECT_THAT(pread64(fd, buf, 1024, 0), SyscallSucceeds());
+  EXPECT_THAT(close(fd), SyscallSucceeds());
+
+  EXPECT_THAT(unlink(name.c_str()), SyscallSucceeds());
+  EXPECT_THAT(unlink(linkname.c_str()), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, SymlinkAtDegradedPermissions_NoRandomSave) {
+  // Drop capabilities that allow us to override file and directory permissions.
+  ASSERT_NO_ERRNO(SetCapability(CAP_DAC_OVERRIDE, false));
+  ASSERT_NO_ERRNO(SetCapability(CAP_DAC_READ_SEARCH, false));
+
+  auto dir = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+  auto file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFileIn(dir.path()));
+
+  int dirfd;
+  ASSERT_THAT(dirfd = open(dir.path().c_str(), O_DIRECTORY, 0),
+              SyscallSucceeds());
+
+  const DisableSave ds;  // Permissions are dropped.
+  EXPECT_THAT(fchmod(dirfd, 0), SyscallSucceeds());
+
+  std::string basename = std::string(Basename(file.path()));
+  EXPECT_THAT(symlinkat("/dangling", dirfd, basename.c_str()),
+              SyscallFailsWithErrno(EACCES));
+  EXPECT_THAT(close(dirfd), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, ReadlinkAtDegradedPermissions_NoRandomSave) {
+  // Drop capabilities that allow us to override file and directory permissions.
+  ASSERT_NO_ERRNO(SetCapability(CAP_DAC_OVERRIDE, false));
+  ASSERT_NO_ERRNO(SetCapability(CAP_DAC_READ_SEARCH, false));
+
+  auto dir = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+  const std::string oldpath = NewTempAbsPathInDir(dir.path());
+  const std::string oldbase = std::string(Basename(oldpath));
+  ASSERT_THAT(symlink("/dangling", oldpath.c_str()), SyscallSucceeds());
+
+  int dirfd;
+  EXPECT_THAT(dirfd = open(dir.path().c_str(), O_DIRECTORY, 0),
+              SyscallSucceeds());
+
+  const DisableSave ds;  // Permissions are dropped.
+  EXPECT_THAT(fchmod(dirfd, 0), SyscallSucceeds());
+
+  char buf[1024];
+  int linksize;
+  EXPECT_THAT(linksize = readlinkat(dirfd, oldbase.c_str(), buf, 1024),
+              SyscallFailsWithErrno(EACCES));
+  EXPECT_THAT(close(dirfd), SyscallSucceeds());
+}
+
+TEST(SymlinkTest, ChmodSymlink) {
+  auto target = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  const std::string newpath = NewTempAbsPath();
+  ASSERT_THAT(symlink(target.path().c_str(), newpath.c_str()),
+              SyscallSucceeds());
+  EXPECT_EQ(FilePermission(newpath), 0777);
+  EXPECT_THAT(chmod(newpath.c_str(), 0666), SyscallSucceeds());
+  EXPECT_EQ(FilePermission(newpath), 0777);
+}
+
+}  // namespace
+
+}  // namespace testing
+}  // namespace gvisor