[PATCH v7 22/28] fanotify: Report FID entry even for zero-length file_handle

[Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>]

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 <krisman@xxxxxxxxxxxxx>
---
 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;
 
-- 
2.33.0