selftests/seccomp: user_notification_addfd check nextfd is available

stable inclusion
from stable-v6.6.30
commit 003af8c23fca24ec6ed5e6cd7a8176b1d27c7357
bugzilla: https://gitee.com/openeuler/kernel/issues/I9MPZ8

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=003af8c23fca24ec6ed5e6cd7a8176b1d27c7357

--------------------------------

commit 8e3c9f9f3a0742cd12b682a1766674253b33fcf0 upstream.

Currently the user_notification_addfd test checks what the next expected
file descriptor will be by incrementing a variable nextfd. This does not
account for file descriptors that may already be open before the test is
started and will cause the test to fail if any exist.

Replace nextfd++ with a function get_next_fd which will check and return
the next available file descriptor.

Signed-off-by: Terry Tritton <terry.tritton@linaro.org>
Link: https://lore.kernel.org/r/20240124141357.1243457-4-terry.tritton@linaro.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>

Author: Terry Tritton

tools/testing/selftests/seccomp/seccomp_bpf.c

@@ -4050,6 +4050,16 @@ TEST(user_notification_filter_empty_threaded)
 	EXPECT_GT((pollfd.revents & POLLHUP) ?: 0, 0);
 }
 
+
+int get_next_fd(int prev_fd)
+{
+	for (int i = prev_fd + 1; i < FD_SETSIZE; ++i) {
+		if (fcntl(i, F_GETFD) == -1)
+			return i;
+	}
+	_exit(EXIT_FAILURE);
+}
+
 TEST(user_notification_addfd)
 {
 	pid_t pid;
@@ -4066,7 +4076,7 @@ TEST(user_notification_addfd)
 	/* There may be arbitrary already-open fds at test start. */
 	memfd = memfd_create("test", 0);
 	ASSERT_GE(memfd, 0);
-	nextfd = memfd + 1;
+	nextfd = get_next_fd(memfd);
 
 	ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
 	ASSERT_EQ(0, ret) {
@@ -4077,7 +4087,8 @@ TEST(user_notification_addfd)
 	/* Check that the basic notification machinery works */
 	listener = user_notif_syscall(__NR_getppid,
 				      SECCOMP_FILTER_FLAG_NEW_LISTENER);
-	ASSERT_EQ(listener, nextfd++);
+	ASSERT_EQ(listener, nextfd);
+	nextfd = get_next_fd(nextfd);
 
 	pid = fork();
 	ASSERT_GE(pid, 0);
@@ -4132,14 +4143,16 @@ TEST(user_notification_addfd)
 
 	/* Verify we can set an arbitrary remote fd */
 	fd = ioctl(listener, SECCOMP_IOCTL_NOTIF_ADDFD, &addfd);
-	EXPECT_EQ(fd, nextfd++);
+	EXPECT_EQ(fd, nextfd);
+	nextfd = get_next_fd(nextfd);
 	EXPECT_EQ(filecmp(getpid(), pid, memfd, fd), 0);
 
 	/* Verify we can set an arbitrary remote fd with large size */
 	memset(&big, 0x0, sizeof(big));
 	big.addfd = addfd;
 	fd = ioctl(listener, SECCOMP_IOCTL_NOTIF_ADDFD_BIG, &big);
-	EXPECT_EQ(fd, nextfd++);
+	EXPECT_EQ(fd, nextfd);
+	nextfd = get_next_fd(nextfd);
 
 	/* Verify we can set a specific remote fd */
 	addfd.newfd = 42;
@@ -4177,7 +4190,8 @@ TEST(user_notification_addfd)
 	 * Child has earlier "low" fds and now 42, so we expect the next
 	 * lowest available fd to be assigned here.
 	 */
-	EXPECT_EQ(fd, nextfd++);
+	EXPECT_EQ(fd, nextfd);
+	nextfd = get_next_fd(nextfd);
 	ASSERT_EQ(filecmp(getpid(), pid, memfd, fd), 0);
 
 	/*