selftests: core: add tests for CLOSE_RANGE_CLOEXEC

check that close_range(initial_fd, last_fd, CLOSE_RANGE_CLOEXEC)
correctly sets the close-on-exec bit for the specified file
descriptors.

Open 100 file descriptors and set the close-on-exec flag for a subset
of them first, then set it for every file descriptor above 2.  Make
sure RLIMIT_NOFILE doesn't affect the result.
Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
Link: https://lore.kernel.org/r/20201118104746.873084-3-gscrivan@redhat.comSigned-off-by: Christian Brauner <christian.brauner@ubuntu.com>

tools/testing/selftests/core/close_range_test.c

@@ -11,6 +11,7 @@
 #include <string.h>
 #include <syscall.h>
 #include <unistd.h>
+#include <sys/resource.h>
 
 #include "../kselftest_harness.h"
 #include "../clone3/clone3_selftests.h"
@@ -23,6 +24,10 @@
 #define CLOSE_RANGE_UNSHARE	(1U << 1)
 #endif
 
+#ifndef CLOSE_RANGE_CLOEXEC
+#define CLOSE_RANGE_CLOEXEC	(1U << 2)
+#endif
+
 static inline int sys_close_range(unsigned int fd, unsigned int max_fd,
 				  unsigned int flags)
 {
@@ -224,4 +229,73 @@ TEST(close_range_unshare_capped)
 	EXPECT_EQ(0, WEXITSTATUS(status));
 }
 
+TEST(close_range_cloexec)
+{
+	int i, ret;
+	int open_fds[101];
+	struct rlimit rlimit;
+
+	for (i = 0; i < ARRAY_SIZE(open_fds); i++) {
+		int fd;
+
+		fd = open("/dev/null", O_RDONLY);
+		ASSERT_GE(fd, 0) {
+			if (errno == ENOENT)
+				XFAIL(return, "Skipping test since /dev/null does not exist");
+		}
+
+		open_fds[i] = fd;
+	}
+
+	ret = sys_close_range(1000, 1000, CLOSE_RANGE_CLOEXEC);
+	if (ret < 0) {
+		if (errno == ENOSYS)
+			XFAIL(return, "close_range() syscall not supported");
+		if (errno == EINVAL)
+			XFAIL(return, "close_range() doesn't support CLOSE_RANGE_CLOEXEC");
+	}
+
+	/* Ensure the FD_CLOEXEC bit is set also with a resource limit in place.  */
+	ASSERT_EQ(0, getrlimit(RLIMIT_NOFILE, &rlimit));
+	rlimit.rlim_cur = 25;
+	ASSERT_EQ(0, setrlimit(RLIMIT_NOFILE, &rlimit));
+
+	/* Set close-on-exec for two ranges: [0-50] and [75-100].  */
+	ret = sys_close_range(open_fds[0], open_fds[50], CLOSE_RANGE_CLOEXEC);
+	ASSERT_EQ(0, ret);
+	ret = sys_close_range(open_fds[75], open_fds[100], CLOSE_RANGE_CLOEXEC);
+	ASSERT_EQ(0, ret);
+
+	for (i = 0; i <= 50; i++) {
+		int flags = fcntl(open_fds[i], F_GETFD);
+
+		EXPECT_GT(flags, -1);
+		EXPECT_EQ(flags & FD_CLOEXEC, FD_CLOEXEC);
+	}
+
+	for (i = 51; i <= 74; i++) {
+		int flags = fcntl(open_fds[i], F_GETFD);
+
+		EXPECT_GT(flags, -1);
+		EXPECT_EQ(flags & FD_CLOEXEC, 0);
+	}
+
+	for (i = 75; i <= 100; i++) {
+		int flags = fcntl(open_fds[i], F_GETFD);
+
+		EXPECT_GT(flags, -1);
+		EXPECT_EQ(flags & FD_CLOEXEC, FD_CLOEXEC);
+	}
+
+	/* Test a common pattern.  */
+	ret = sys_close_range(3, UINT_MAX, CLOSE_RANGE_CLOEXEC);
+	for (i = 0; i <= 100; i++) {
+		int flags = fcntl(open_fds[i], F_GETFD);
+
+		EXPECT_GT(flags, -1);
+		EXPECT_EQ(flags & FD_CLOEXEC, FD_CLOEXEC);
+	}
+}
+
+
 TEST_HARNESS_MAIN