// 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 <errno.h> #include <fcntl.h> #include <string.h> #include <unistd.h> #include <string> #include "gtest/gtest.h" #include "absl/time/clock.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. Regression test for b/31782115. 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 auto oldfile = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile()); const auto newfile = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile()); EXPECT_THAT(symlink(oldfile.path().c_str(), newfile.path().c_str()), SyscallFailsWithErrno(EEXIST)); } TEST(SymlinkTest, CannotSymlinkOverExistingDir) { const auto oldfile = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile()); const auto newdir = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir()); EXPECT_THAT(symlink(oldfile.path().c_str(), newdir.path().c_str()), SyscallFailsWithErrno(EEXIST)); } 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 auto file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile()); // We are going to assert that the symlink inode id is the same as the linked // file's inode id. In order for the inode id to be stable across // save/restore, it must be kept open. The FileDescriptor type will do that // for us automatically. auto fd = ASSERT_NO_ERRNO_AND_VALUE(Open(file.path(), O_RDWR)); struct stat file_st; EXPECT_THAT(fstat(fd.get(), &file_st), SyscallSucceeds()); const std::string link = NewTempAbsPath(); EXPECT_THAT(symlink(file.path().c_str(), link.c_str()), SyscallSucceeds()); EXPECT_EQ(FilePermission(link), 0777); auto linkfd = ASSERT_NO_ERRNO_AND_VALUE(Open(link.c_str(), O_RDWR)); struct stat link_st; EXPECT_THAT(fstat(linkfd.get(), &link_st), SyscallSucceeds()); // Check that in fact newname points to the file we expect. EXPECT_EQ(file_st.st_dev, link_st.st_dev); EXPECT_EQ(file_st.st_ino, link_st.st_ino); } 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); } // Test that following a symlink updates the atime on the symlink. TEST(SymlinkTest, FollowUpdatesATime) { const auto file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile()); const std::string link = NewTempAbsPath(); EXPECT_THAT(symlink(file.path().c_str(), link.c_str()), SyscallSucceeds()); // Lstat the symlink. struct stat st_before_follow; ASSERT_THAT(lstat(link.c_str(), &st_before_follow), SyscallSucceeds()); // Let the clock advance. absl::SleepFor(absl::Seconds(1)); // Open the file via the symlink. int fd; ASSERT_THAT(fd = open(link.c_str(), O_RDWR, 0666), SyscallSucceeds()); FileDescriptor fd_closer(fd); // Lstat the symlink again, and check that atime is updated. struct stat st_after_follow; ASSERT_THAT(lstat(link.c_str(), &st_after_follow), SyscallSucceeds()); EXPECT_LT(st_before_follow.st_atime, st_after_follow.st_atime); } class ParamSymlinkTest : public ::testing::TestWithParam<std::string> {}; // Test that creating an existing symlink with creat will create the target. TEST_P(ParamSymlinkTest, CreatLinkCreatesTarget) { const std::string target = GetParam(); const std::string linkpath = NewTempAbsPath(); ASSERT_THAT(symlink(target.c_str(), linkpath.c_str()), SyscallSucceeds()); int fd; EXPECT_THAT(fd = creat(linkpath.c_str(), 0666), SyscallSucceeds()); ASSERT_THAT(close(fd), SyscallSucceeds()); ASSERT_THAT(chdir(GetAbsoluteTestTmpdir().c_str()), SyscallSucceeds()); struct stat st; EXPECT_THAT(stat(target.c_str(), &st), SyscallSucceeds()); ASSERT_THAT(unlink(linkpath.c_str()), SyscallSucceeds()); ASSERT_THAT(unlink(target.c_str()), SyscallSucceeds()); } // Test that opening an existing symlink with O_CREAT will create the target. TEST_P(ParamSymlinkTest, OpenLinkCreatesTarget) { const std::string target = GetParam(); const std::string linkpath = NewTempAbsPath(); ASSERT_THAT(symlink(target.c_str(), linkpath.c_str()), SyscallSucceeds()); int fd; EXPECT_THAT(fd = open(linkpath.c_str(), O_CREAT, 0666), SyscallSucceeds()); ASSERT_THAT(close(fd), SyscallSucceeds()); ASSERT_THAT(chdir(GetAbsoluteTestTmpdir().c_str()), SyscallSucceeds()); struct stat st; EXPECT_THAT(stat(target.c_str(), &st), SyscallSucceeds()); ASSERT_THAT(unlink(linkpath.c_str()), SyscallSucceeds()); ASSERT_THAT(unlink(target.c_str()), SyscallSucceeds()); } // Test that opening a self-symlink with O_CREAT will fail with ELOOP. TEST_P(ParamSymlinkTest, CreateExistingSelfLink) { ASSERT_THAT(chdir(GetAbsoluteTestTmpdir().c_str()), SyscallSucceeds()); const std::string linkpath = GetParam(); ASSERT_THAT(symlink(linkpath.c_str(), linkpath.c_str()), SyscallSucceeds()); EXPECT_THAT(open(linkpath.c_str(), O_CREAT, 0666), SyscallFailsWithErrno(ELOOP)); ASSERT_THAT(unlink(linkpath.c_str()), SyscallSucceeds()); } // Test that opening a file that is a symlink to its parent directory fails // with ELOOP. TEST_P(ParamSymlinkTest, CreateExistingParentLink) { ASSERT_THAT(chdir(GetAbsoluteTestTmpdir().c_str()), SyscallSucceeds()); const std::string linkpath = GetParam(); const std::string target = JoinPath(linkpath, "child"); ASSERT_THAT(symlink(target.c_str(), linkpath.c_str()), SyscallSucceeds()); EXPECT_THAT(open(linkpath.c_str(), O_CREAT, 0666), SyscallFailsWithErrno(ELOOP)); ASSERT_THAT(unlink(linkpath.c_str()), SyscallSucceeds()); } // Test that opening an existing symlink with O_CREAT|O_EXCL will fail with // EEXIST. TEST_P(ParamSymlinkTest, OpenLinkExclFails) { const std::string target = GetParam(); const std::string linkpath = NewTempAbsPath(); ASSERT_THAT(symlink(target.c_str(), linkpath.c_str()), SyscallSucceeds()); EXPECT_THAT(open(linkpath.c_str(), O_CREAT | O_EXCL, 0666), SyscallFailsWithErrno(EEXIST)); ASSERT_THAT(unlink(linkpath.c_str()), SyscallSucceeds()); } // Test that opening an existing symlink with O_CREAT|O_NOFOLLOW will fail with // ELOOP. TEST_P(ParamSymlinkTest, OpenLinkNoFollowFails) { const std::string target = GetParam(); const std::string linkpath = NewTempAbsPath(); ASSERT_THAT(symlink(target.c_str(), linkpath.c_str()), SyscallSucceeds()); EXPECT_THAT(open(linkpath.c_str(), O_CREAT | O_NOFOLLOW, 0666), SyscallFailsWithErrno(ELOOP)); ASSERT_THAT(unlink(linkpath.c_str()), SyscallSucceeds()); } INSTANTIATE_TEST_SUITE_P(AbsAndRelTarget, ParamSymlinkTest, ::testing::Values(NewTempAbsPath(), NewTempRelPath())); } // namespace } // namespace testing } // namespace gvisor