selftest: add tests for O_EMPTYPATH

Add tests for the new O_EMPTYPATH flag of openat(2)/openat2(2).

Also, the current openat2 tests include a helper header file that
defines the necessary structs and constants to use openat2(2), such as
struct open_how. This may result in conflicting definitions when the
system header openat2.h is present as well.

So add openat2.h generated by 'make headers' to the uapi header
files in ./tools/include and remove the helper file definitions of
the current openat2 selftests.

Signed-off-by: Jori Koolstra <jkoolstra@xs4all.nl>
Link: https://patch.msgid.link/20260424114611.1678641-3-jkoolstra@xs4all.nl
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

tools/include/uapi/linux/openat2.h

@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _LINUX_OPENAT2_H
+#define _LINUX_OPENAT2_H
+
+#include <linux/types.h>
+
+/*
+ * Arguments for how openat2(2) should open the target path. If only @flags and
+ * @mode are non-zero, then openat2(2) operates very similarly to openat(2).
+ *
+ * However, unlike openat(2), unknown or invalid bits in @flags result in
+ * -EINVAL rather than being silently ignored. @mode must be zero unless one of
+ * {O_CREAT, O_TMPFILE} are set.
+ *
+ * @flags: O_* flags.
+ * @mode: O_CREAT/O_TMPFILE file mode.
+ * @resolve: RESOLVE_* flags.
+ */
+struct open_how {
+	__u64 flags;
+	__u64 mode;
+	__u64 resolve;
+};
+
+/* how->resolve flags for openat2(2). */
+#define RESOLVE_NO_XDEV		0x01 /* Block mount-point crossings
+					(includes bind-mounts). */
+#define RESOLVE_NO_MAGICLINKS	0x02 /* Block traversal through procfs-style
+					"magic-links". */
+#define RESOLVE_NO_SYMLINKS	0x04 /* Block traversal through all symlinks
+					(implies OEXT_NO_MAGICLINKS) */
+#define RESOLVE_BENEATH		0x08 /* Block "lexical" trickery like
+					"..", symlinks, and absolute
+					paths which escape the dirfd. */
+#define RESOLVE_IN_ROOT		0x10 /* Make all jumps to "/" and ".."
+					be scoped inside the dirfd
+					(similar to chroot(2)). */
+#define RESOLVE_CACHED		0x20 /* Only complete if resolution can be
+					completed through cached lookup. May
+					return -EAGAIN if that's not
+					possible. */
+
+#endif /* _LINUX_OPENAT2_H */

tools/testing/selftests/filesystems/openat2/Makefile

@@ -1,8 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
 CFLAGS += $(KHDR_INCLUDES)
-CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined
-TEST_GEN_PROGS := openat2_test resolve_test rename_attack_test
+CFLAGS += -Wall -O2 -g -fsanitize=address -fsanitize=undefined $(TOOLS_INCLUDES)
+TEST_GEN_PROGS := openat2_test resolve_test rename_attack_test emptypath_test
 
 # gcc requires -static-libasan in order to ensure that Address Sanitizer's
 # library is the first one loaded. However, clang already statically links the

tools/testing/selftests/filesystems/openat2/emptypath_test.c

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define __SANE_USERSPACE_TYPES__
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "kselftest.h"
+
+#ifndef O_EMPTYPATH
+#define O_EMPTYPATH	(1 << 26)
+#endif
+
+int main(void)
+{
+	int opath_fd, reopen_fd;
+	const char *path = "/tmp/emptypath_test";
+
+	ksft_print_header();
+	ksft_set_plan(2);
+
+	opath_fd = open(path, O_CREAT | O_WRONLY, S_IRWXU);
+	if (opath_fd < 0)
+		ksft_exit_fail_msg("create %s: %m\n", path);
+	close(opath_fd);
+
+	opath_fd = open(path, O_PATH);
+	if (opath_fd < 0)
+		ksft_exit_fail_msg("open %s O_PATH: %m\n", path);
+
+	reopen_fd = openat(opath_fd, "", O_RDONLY);
+	if (reopen_fd < 0 && errno == ENOENT)
+		ksft_test_result_pass("empty path without O_EMPTYPATH returns ENOENT\n");
+	else if (reopen_fd >= 0) {
+		ksft_test_result_fail("empty path without O_EMPTYPATH unexpectedly succeeded\n");
+		close(reopen_fd);
+	} else {
+		ksft_test_result_fail("empty path without O_EMPTYPATH: expected ENOENT, got %m\n");
+	}
+
+	reopen_fd = openat(opath_fd, "", O_RDONLY | O_EMPTYPATH);
+
+	if (reopen_fd < 0 && errno == EINVAL)
+		ksft_exit_skip("O_EMPTYPATH not supported\n");
+
+	if (reopen_fd >= 0) {
+		ksft_test_result_pass("O_EMPTYPATH reopens O_PATH fd\n");
+		close(reopen_fd);
+	} else {
+		ksft_test_result_fail("O_EMPTYPATH failed: %m\n");
+	}
+
+	unlink(path);
+	ksft_finished();
+}

tools/testing/selftests/filesystems/openat2/helpers.h

@@ -15,47 +15,14 @@
 #include <limits.h>
 #include <linux/types.h>
 #include <linux/unistd.h>
+#include <linux/openat2.h>
 #include "kselftest_harness.h"
 
 #define BUILD_BUG_ON(e) ((void)(sizeof(struct { int:(-!!(e)); })))
 
-/*
- * Arguments for how openat2(2) should open the target path. If @resolve is
- * zero, then openat2(2) operates very similarly to openat(2).
- *
- * However, unlike openat(2), unknown bits in @flags result in -EINVAL rather
- * than being silently ignored. @mode must be zero unless one of {O_CREAT,
- * O_TMPFILE} are set.
- *
- * @flags: O_* flags.
- * @mode: O_CREAT/O_TMPFILE file mode.
- * @resolve: RESOLVE_* flags.
- */
-struct open_how {
-	__u64 flags;
-	__u64 mode;
-	__u64 resolve;
-};
-
 #define OPEN_HOW_SIZE_VER0	24 /* sizeof first published struct */
 #define OPEN_HOW_SIZE_LATEST	OPEN_HOW_SIZE_VER0
 
-#ifndef RESOLVE_IN_ROOT
-/* how->resolve flags for openat2(2). */
-#define RESOLVE_NO_XDEV		0x01 /* Block mount-point crossings
-					(includes bind-mounts). */
-#define RESOLVE_NO_MAGICLINKS	0x02 /* Block traversal through procfs-style
-					"magic-links". */
-#define RESOLVE_NO_SYMLINKS	0x04 /* Block traversal through all symlinks
-					(implies OEXT_NO_MAGICLINKS) */
-#define RESOLVE_BENEATH		0x08 /* Block "lexical" trickery like
-					"..", symlinks, and absolute
-					paths which escape the dirfd. */
-#define RESOLVE_IN_ROOT		0x10 /* Make all jumps to "/" and ".."
-					be scoped inside the dirfd
-					(similar to chroot(2)). */
-#endif /* RESOLVE_IN_ROOT */
-
 __maybe_unused
 static bool needs_openat2(const struct open_how *how)
 {