Non-inode errors will reported with an empty file_handle.  In
preparation for that, allow some events to print the FID record even if
there isn't any file_handle encoded

Even though FILEID_ROOT is used internally, make zero-length file
handles be reported as FILEID_INVALID.

Signed-off-by: Gabriel Krisman Bertazi <redacted>
---
 fs/notify/fanotify/fanotify_user.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 5324890500fc..39cf8ba4a6ce 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c

@@ -127,6 +127,16 @@ static int fanotify_fid_info_len(int fh_len, int name_len)
                       FANOTIFY_EVENT_ALIGN);
 }

+static bool fanotify_event_allows_empty_fh(struct fanotify_event *event)
+{
+       switch (event->type) {
+       case FANOTIFY_EVENT_TYPE_FS_ERROR:
+               return true;
+       default:
+               return false;
+       }
+}
+
 static size_t fanotify_event_len(unsigned int info_mode,
                                 struct fanotify_event *event)
 {

@@ -157,7 +167,7 @@ static size_t fanotify_event_len(unsigned int info_mode,
        if (info_mode & FAN_REPORT_PIDFD)
                event_len += FANOTIFY_PIDFD_INFO_HDR_LEN;

-       if (fh_len)
+       if (fh_len || fanotify_event_allows_empty_fh(event))
                event_len += fanotify_fid_info_len(fh_len, dot_len);

        return event_len;

@@ -338,9 +348,6 @@ static int copy_fid_info_to_user(__kernel_fsid_t *fsid, struct fanotify_fh *fh,
        pr_debug("%s: fh_len=%zu name_len=%zu, info_len=%zu, count=%zu\n",
                 __func__, fh_len, name_len, info_len, count);

-       if (!fh_len)
-               return 0;
-
        if (WARN_ON_ONCE(len < sizeof(info) || len > count))
                return -EFAULT;

@@ -375,6 +382,11 @@ static int copy_fid_info_to_user(__kernel_fsid_t *fsid, struct fanotify_fh *fh,

        handle.handle_type = fh->type;
        handle.handle_bytes = fh_len;
+
+       /* Mangle handle_type for bad file_handle */
+       if (!fh_len)
+               handle.handle_type = FILEID_INVALID;
+
        if (copy_to_user(buf, &handle, sizeof(handle)))
                return -EFAULT;

@@ -467,7 +479,8 @@ static int copy_info_records_to_user(struct fanotify_event *event,
                total_bytes += ret;
        }

-       if (fanotify_event_object_fh_len(event)) {
+       if (fanotify_event_object_fh_len(event) ||
+           fanotify_event_allows_empty_fh(event)) {
                const char *dot = NULL;
                int dot_len = 0;