selftests/bpf: add a test for iter/task_vma for short-lived processes

When a task iterator traverses vma(s), it is possible task->mm might
become invalid in the middle of traversal and this may cause kernel
misbehave (e.g., crash)

This test case creates iterators repeatedly and forks short-lived
processes in the background to detect this bug.  The test will last
for 3 seconds to get the chance to trigger the issue.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221216221855.4122288-3-kuifeng@meta.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index 6f8ed61fc4b4a8696779afa8e746d9ed6541e638..3af6450763e9ac946c8b7f83f5cb509ced004b6e 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -1465,6 +1465,77 @@ out:
        bpf_iter_task_vma__destroy(skel);
 }
 
+static void test_task_vma_dead_task(void)
+{
+       struct bpf_iter_task_vma *skel;
+       int wstatus, child_pid = -1;
+       time_t start_tm, cur_tm;
+       int err, iter_fd = -1;
+       int wait_sec = 3;
+
+       skel = bpf_iter_task_vma__open();
+       if (!ASSERT_OK_PTR(skel, "bpf_iter_task_vma__open"))
+               return;
+
+       skel->bss->pid = getpid();
+
+       err = bpf_iter_task_vma__load(skel);
+       if (!ASSERT_OK(err, "bpf_iter_task_vma__load"))
+               goto out;
+
+       skel->links.proc_maps = bpf_program__attach_iter(
+               skel->progs.proc_maps, NULL);
+
+       if (!ASSERT_OK_PTR(skel->links.proc_maps, "bpf_program__attach_iter")) {
+               skel->links.proc_maps = NULL;
+               goto out;
+       }
+
+       start_tm = time(NULL);
+       cur_tm = start_tm;
+
+       child_pid = fork();
+       if (child_pid == 0) {
+               /* Fork short-lived processes in the background. */
+               while (cur_tm < start_tm + wait_sec) {
+                       system("echo > /dev/null");
+                       cur_tm = time(NULL);
+               }
+               exit(0);
+       }
+
+       if (!ASSERT_GE(child_pid, 0, "fork_child"))
+               goto out;
+
+       while (cur_tm < start_tm + wait_sec) {
+               iter_fd = bpf_iter_create(bpf_link__fd(skel->links.proc_maps));
+               if (!ASSERT_GE(iter_fd, 0, "create_iter"))
+                       goto out;
+
+               /* Drain all data from iter_fd. */
+               while (cur_tm < start_tm + wait_sec) {
+                       err = read_fd_into_buffer(iter_fd, task_vma_output, CMP_BUFFER_SIZE);
+                       if (!ASSERT_GE(err, 0, "read_iter_fd"))
+                               goto out;
+
+                       cur_tm = time(NULL);
+
+                       if (err == 0)
+                               break;
+               }
+
+               close(iter_fd);
+               iter_fd = -1;
+       }
+
+       check_bpf_link_info(skel->progs.proc_maps);
+
+out:
+       waitpid(child_pid, &wstatus, 0);
+       close(iter_fd);
+       bpf_iter_task_vma__destroy(skel);
+}
+
 void test_bpf_sockmap_map_iter_fd(void)
 {
        struct bpf_iter_sockmap *skel;
@@ -1586,6 +1657,8 @@ void test_bpf_iter(void)
                test_task_file();
        if (test__start_subtest("task_vma"))
                test_task_vma();
+       if (test__start_subtest("task_vma_dead_task"))
+               test_task_vma_dead_task();
        if (test__start_subtest("task_btf"))
                test_task_btf();
        if (test__start_subtest("tcp4"))