selftests/seccomp: user_notification_addfd check nextfd is available

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>

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 38f6514699682b8f318e7a1d80c0faf299fe1eba..be0fece2596d994b4ecbe2c3c1b9a4d6f9fa04a8 100644 (file)
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -4037,6 +4037,16 @@ 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;
@@ -4053,7 +4063,7 @@ 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) {
@@ -4064,7 +4074,8 @@ 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);
@@ -4119,14 +4130,16 @@ 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;
@@ -4164,7 +4177,8 @@ 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);
 
        /*