[vfs] overlayfs: Fix socket tests.

- BindSocketThenOpen test was expecting the incorrect error when opening
  a socket. Fixed that.
- VirtualFilesystem.BindEndpointAt should not require pop.Path.Begin.Ok()
  because the filesystem implementations do not need to walk to the parent
  dentry. This check also exists for MknodAt, MkdirAt, RmdirAt, SymlinkAt and
  UnlinkAt but those filesystem implementations also need to walk to the parent
  denty. So that check is valid. Added some syscall tests to test this.

PiperOrigin-RevId: 330625220

4 files changed, 39 insertions, 0 deletions

diff --git a/test/syscalls/linux/mkdir.cc b/test/syscalls/linux/mkdir.cc
index 4036a9275..27758203d 100644
--- a/test/syscalls/linux/mkdir.cc
+++ b/test/syscalls/linux/mkdir.cc
@@ -82,6 +82,13 @@ TEST_F(MkdirTest, FailsOnDirWithoutWritePerms) {
               SyscallFailsWithErrno(EACCES));
 }
 
+TEST_F(MkdirTest, MkdirAtEmptyPath) {
+  ASSERT_THAT(mkdir(dirname_.c_str(), 0777), SyscallSucceeds());
+  auto fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(dirname_, O_RDONLY | O_DIRECTORY, 0666));
+  EXPECT_THAT(mkdirat(fd.get(), "", 0777), SyscallFailsWithErrno(ENOENT));
+}
+
 }  // namespace
 
 }  // namespace testing
diff --git a/test/syscalls/linux/mknod.cc b/test/syscalls/linux/mknod.cc
index 2ba8c11b8..89e4564e8 100644
--- a/test/syscalls/linux/mknod.cc
+++ b/test/syscalls/linux/mknod.cc
@@ -203,6 +203,14 @@ TEST(MknodTest, FifoTruncNoOp) {
   EXPECT_THAT(ftruncate(wfd.get(), 0), SyscallFailsWithErrno(EINVAL));
 }
 
+TEST(MknodTest, MknodAtEmptyPath) {
+  auto dir = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+  auto fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(dir.path(), O_RDONLY | O_DIRECTORY, 0666));
+  EXPECT_THAT(mknodat(fd.get(), "", S_IFREG | 0777, 0),
+              SyscallFailsWithErrno(ENOENT));
+}
+
 }  // namespace
 
 }  // namespace testing
diff --git a/test/syscalls/linux/symlink.cc b/test/syscalls/linux/symlink.cc
index aa1f32c85..a5d7efe94 100644
--- a/test/syscalls/linux/symlink.cc
+++ b/test/syscalls/linux/symlink.cc
@@ -326,6 +326,16 @@ TEST(SymlinkTest, FollowUpdatesATime) {
   EXPECT_LT(st_before_follow.st_atime, st_after_follow.st_atime);
 }
 
+TEST(SymlinkTest, SymlinkAtEmptyPath) {
+  auto file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  auto dir = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+
+  auto fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(dir.path(), O_RDONLY | O_DIRECTORY, 0666));
+  EXPECT_THAT(symlinkat(file.path().c_str(), fd.get(), ""),
+              SyscallFailsWithErrno(ENOENT));
+}
+
 class ParamSymlinkTest : public ::testing::TestWithParam<std::string> {};
 
 // Test that creating an existing symlink with creat will create the target.
diff --git a/test/syscalls/linux/unlink.cc b/test/syscalls/linux/unlink.cc
index 2040375c9..061e2e0f1 100644
--- a/test/syscalls/linux/unlink.cc
+++ b/test/syscalls/linux/unlink.cc
@@ -208,6 +208,20 @@ TEST(RmdirTest, CanRemoveWithTrailingSlashes) {
   ASSERT_THAT(rmdir(slashslash.c_str()), SyscallSucceeds());
 }
 
+TEST(UnlinkTest, UnlinkAtEmptyPath) {
+  auto dir = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+
+  auto file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFileIn(dir.path()));
+  auto fd = ASSERT_NO_ERRNO_AND_VALUE(Open(file.path(), O_RDWR, 0666));
+  EXPECT_THAT(unlinkat(fd.get(), "", 0), SyscallFailsWithErrno(ENOENT));
+
+  auto dirInDir = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDirIn(dir.path()));
+  auto dirFD = ASSERT_NO_ERRNO_AND_VALUE(
+      Open(dirInDir.path(), O_RDONLY | O_DIRECTORY, 0666));
+  EXPECT_THAT(unlinkat(dirFD.get(), "", AT_REMOVEDIR),
+              SyscallFailsWithErrno(ENOENT));
+}
+
 }  // namespace
 
 }  // namespace testing