[1/7] syscalls/fanotify20: Introduce helpers for FAN_FS_ERROR test

fanotify20 is a new test validating the FAN_FS_ERROR file system error
event.  This adds some basic structure for the next patches.

The strategy for error reporting testing in fanotify20 goes like this:

  - Generate a broken filesystem
  - Start FAN_FS_ERROR monitoring group
  - Make the file system  notice the error through ordinary operations
  - Observe the event generated

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 testcases/kernel/syscalls/fanotify/.gitignore |   1 +
 .../kernel/syscalls/fanotify/fanotify20.c     | 135 ++++++++++++++++++
 2 files changed, 136 insertions(+)
 create mode 100644 testcases/kernel/syscalls/fanotify/fanotify20.c

On Tue, Aug 3, 2021 at 12:47 AM Gabriel Krisman Bertazi
<krisman@collabora.com> wrote:
>
> fanotify20 is a new test validating the FAN_FS_ERROR file system error
> event.  This adds some basic structure for the next patches.
>
> The strategy for error reporting testing in fanotify20 goes like this:
>
>   - Generate a broken filesystem
>   - Start FAN_FS_ERROR monitoring group
>   - Make the file system  notice the error through ordinary operations
>   - Observe the event generated
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
> ---
>  testcases/kernel/syscalls/fanotify/.gitignore |   1 +
>  .../kernel/syscalls/fanotify/fanotify20.c     | 135 ++++++++++++++++++
>  2 files changed, 136 insertions(+)
>  create mode 100644 testcases/kernel/syscalls/fanotify/fanotify20.c
>
> diff --git a/testcases/kernel/syscalls/fanotify/.gitignore b/testcases/kernel/syscalls/fanotify/.gitignore
> index 9554b16b196e..c99e6fff76d6 100644
> --- a/testcases/kernel/syscalls/fanotify/.gitignore
> +++ b/testcases/kernel/syscalls/fanotify/.gitignore
> @@ -17,4 +17,5 @@
>  /fanotify17
>  /fanotify18
>  /fanotify19
> +/fanotify20
>  /fanotify_child
> diff --git a/testcases/kernel/syscalls/fanotify/fanotify20.c b/testcases/kernel/syscalls/fanotify/fanotify20.c
> new file mode 100644
> index 000000000000..50531bd99cc9
> --- /dev/null
> +++ b/testcases/kernel/syscalls/fanotify/fanotify20.c
> @@ -0,0 +1,135 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (c) 2021 Collabora Ltd.
> + *
> + * Author: Gabriel Krisman Bertazi <gabriel@krisman.be>
> + * Based on previous work by Amir Goldstein <amir73il@gmail.com>
> + */
> +
> +/*\
> + * [Description]
> + * Check fanotify FAN_ERROR_FS events triggered by intentionally
> + * corrupted filesystems:
> + *
> + * - Generate a broken filesystem
> + * - Start FAN_FS_ERROR monitoring group
> + * - Make the file system notice the error through ordinary operations
> + * - Observe the event generated
> + */
> +
> +#define _GNU_SOURCE
> +#include "config.h"
> +
> +#include <stdio.h>
> +#include <sys/stat.h>
> +#include <sys/types.h>
> +#include <errno.h>
> +#include <string.h>
> +#include <sys/mount.h>
> +#include <sys/syscall.h>
> +#include "tst_test.h"
> +#include <sys/fanotify.h>
> +#include <sys/types.h>
> +#include <fcntl.h>
> +
> +#ifdef HAVE_SYS_FANOTIFY_H
> +#include "fanotify.h"
> +
> +#ifndef FAN_FS_ERROR
> +#define FAN_FS_ERROR           0x00008000
> +#endif
> +
> +#define BUF_SIZE 256
> +static char event_buf[BUF_SIZE];
> +int fd_notify;
> +
> +#define MOUNT_PATH "test_mnt"
> +
> +static const struct test_case {
> +       char *name;
> +       void (*trigger_error)(void);
> +       void (*prepare_fs)(void);
> +} testcases[] = {
> +};
> +
> +int check_error_event_metadata(struct fanotify_event_metadata *event)
> +{
> +       int fail = 0;
> +
> +       if (event->mask != FAN_FS_ERROR) {
> +               fail++;
> +               tst_res(TFAIL, "got unexpected event %llx",
> +                       (unsigned long long)event->mask);
> +       }
> +
> +       if (event->fd != FAN_NOFD) {
> +               fail++;
> +               tst_res(TFAIL, "Weird FAN_FD %llx",
> +                       (unsigned long long)event->mask);
> +       }
> +       return fail;
> +}
> +
> +void check_event(char *buf, size_t len, const struct test_case *ex)
> +{
> +       struct fanotify_event_metadata *event =
> +               (struct fanotify_event_metadata *) buf;
> +
> +       if (len < FAN_EVENT_METADATA_LEN)
> +               tst_res(TFAIL, "No event metadata found");
> +
> +       if (check_error_event_metadata(event))
> +               return;
> +
> +       tst_res(TPASS, "Successfully received: %s", ex->name);
> +}
> +
> +static void do_test(unsigned int i)
> +{
> +       const struct test_case *tcase = &testcases[i];
> +       size_t read_len;
> +
> +       tcase->trigger_error();
> +
> +       read_len = SAFE_READ(0, fd_notify, event_buf, BUF_SIZE);
> +
> +       check_event(event_buf, read_len, tcase);
> +}
> +
> +static void setup(void)
> +{
> +       unsigned long i;
> +
> +       for (i = 0; i < ARRAY_SIZE(testcases); i++)
> +               if (testcases[i].prepare_fs)
> +                       testcases[i].prepare_fs();
> +

Why is prepare_fs called up front and not on every test case?

> +       fd_notify = SAFE_FANOTIFY_INIT(FAN_CLASS_NOTIF|FAN_REPORT_FID,
> +                                      O_RDONLY);
> +
> +       SAFE_FANOTIFY_MARK(fd_notify, FAN_MARK_ADD|FAN_MARK_FILESYSTEM,
> +                          FAN_FS_ERROR, AT_FDCWD, MOUNT_PATH);

This will cause test to fail on old kernels.
You need to start this test with
fanotify_events_supported_by_kernel(FAN_FS_ERROR)
but you cannot use it as is.

Create a macro like
REQUIRE_FANOTIFY_INIT_FLAGS_SUPPORTED_ON_FS
which calls fanotify_init_flags_err_msg(...fanotify_events_supported_by_kernel())
and pass init flags as argument to fanotify_events_supported_by_kernel()
instead of using hardcoded flags FAN_CLASS_CONTENT.


> +}
> +
> +static void cleanup(void)
> +{
> +       if (fd_notify > 0)
> +               SAFE_CLOSE(fd_notify);
> +}
> +
> +static struct tst_test test = {
> +       .test = do_test,
> +       .tcnt = ARRAY_SIZE(testcases),
> +       .setup = setup,
> +       .cleanup = cleanup,
> +       .mount_device = 1,
> +       .mntpoint = MOUNT_PATH,
> +       .all_filesystems = 0,

This is 0 by default

Thanks,
Amir.