[libc] Implement faccessat (#161065)

#160404

- Implement POSIX function "faccessat"
- Remove redundant param in facessat syscall in access implementation,
faccessat syscall does not take a flags arg

1 files changed, 115 insertions, 0 deletions

diff --git a/libc/test/src/unistd/faccessat_test.cpp b/libc/test/src/unistd/faccessat_test.cpp
new file mode 100644
index 000000000000..6280b147c6d5
--- /dev/null
+++ b/libc/test/src/unistd/faccessat_test.cpp
@@ -0,0 +1,115 @@
+//===-- Unittests for faccessat -------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/fcntl/open.h"
+#include "src/unistd/close.h"
+#include "src/unistd/faccessat.h"
+#include "src/unistd/unlink.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/Test.h"
+
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+namespace {
+
+using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Fails;
+using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
+
+using LlvmLibcFaccessatTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcFaccessatTest, WithAtFdcwd) {
+  // Test access checks on a file with AT_FDCWD and no flags, equivalent to
+  // access().
+  constexpr const char *FILENAME = "faccessat_basic.test";
+  auto TEST_FILE = libc_make_test_file_path(FILENAME);
+
+  // Check permissions on a file with full permissions
+  int fd = LIBC_NAMESPACE::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_GT(fd, 0);
+  ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0));
+
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(AT_FDCWD, TEST_FILE, F_OK, 0),
+              Succeeds(0));
+  ASSERT_THAT(
+      LIBC_NAMESPACE::faccessat(AT_FDCWD, TEST_FILE, X_OK | W_OK | R_OK, 0),
+      Succeeds(0));
+  ASSERT_THAT(LIBC_NAMESPACE::unlink(TEST_FILE), Succeeds(0));
+
+  // Check permissions on a file with execute-only permission
+  fd = LIBC_NAMESPACE::open(TEST_FILE, O_WRONLY | O_CREAT, S_IXUSR);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_GT(fd, 0);
+  ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0));
+
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(AT_FDCWD, TEST_FILE, F_OK, 0),
+              Succeeds(0));
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(AT_FDCWD, TEST_FILE, X_OK, 0),
+              Succeeds(0));
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(AT_FDCWD, TEST_FILE, R_OK, 0),
+              Fails(EACCES));
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(AT_FDCWD, TEST_FILE, W_OK, 0),
+              Fails(EACCES));
+  ASSERT_THAT(LIBC_NAMESPACE::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST_F(LlvmLibcFaccessatTest, NonExistentFile) {
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(AT_FDCWD, "faccessat_nonexistent.test",
+                                        F_OK, 0),
+              Fails(ENOENT));
+}
+
+TEST_F(LlvmLibcFaccessatTest, AtEaccess) {
+  // With AT_EACCESS, faccessat checks permissions using the effective user ID,
+  // but the effective and real user ID will be the same here and changing that
+  // is not feasible in a test, so this is just a basic sanity check.
+  constexpr const char *FILENAME = "faccessat_eaccess.test";
+  auto TEST_FILE = libc_make_test_file_path(FILENAME);
+
+  int fd = LIBC_NAMESPACE::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_GT(fd, 0);
+  ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0));
+
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(AT_FDCWD, TEST_FILE, X_OK | W_OK | R_OK,
+                                        AT_EACCESS),
+              Succeeds(0));
+
+  ASSERT_THAT(LIBC_NAMESPACE::unlink(TEST_FILE), Succeeds(0));
+}
+
+TEST_F(LlvmLibcFaccessatTest, AtEmptyPath) {
+  constexpr const char *FILENAME = "faccessat_atemptypath.test";
+  auto TEST_FILE = libc_make_test_file_path(FILENAME);
+
+  int fd = LIBC_NAMESPACE::open(TEST_FILE, O_WRONLY | O_CREAT, S_IRWXU);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_GT(fd, 0);
+
+  // Check permissions on the file referred to by fd
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(fd, "", F_OK, AT_EMPTY_PATH),
+              Succeeds(0));
+  ASSERT_THAT(
+      LIBC_NAMESPACE::faccessat(fd, "", X_OK | W_OK | R_OK, AT_EMPTY_PATH),
+      Succeeds(0));
+
+  ASSERT_THAT(LIBC_NAMESPACE::close(fd), Succeeds(0));
+  ASSERT_THAT(LIBC_NAMESPACE::unlink(TEST_FILE), Succeeds(0));
+
+  // Check permissions on the current working directory
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(AT_FDCWD, "", F_OK, AT_EMPTY_PATH),
+              Succeeds(0));
+  ASSERT_THAT(LIBC_NAMESPACE::faccessat(AT_FDCWD, "", X_OK | W_OK | R_OK,
+                                        AT_EMPTY_PATH),
+              Succeeds(0));
+}
+
+} // namespace