[PATCH v4 15/15] fanotify: report FAN_ONDIR to listener with FAN_REPORT_FID

[Amir Goldstein <amir73il@gmail.com>]

dirent modification events (create/delete/move) do not carry the
child entry name/inode information. Instead, we report FAN_ONDIR
for mkdir/rmdir so user can differentiate them from creat/unlink.

For backward compatibility and consistency, do not report FAN_ONDIR
to user in legacy fanotify mode (reporting fd) and report FAN_ONDIR
to user in FAN_REPORT_FID mode for all event types.

Unlike legacy fanotify events (open/access/close), dirent events
for subdir entries (mkdir/rmdir) will be reported regardless if
user requested FAN_ONDIR, but the FAN_ONDIR flag itself will only
be reported if the user asked for it.

Cc: <linux-api@vger.kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify.c | 31 +++++++++++++++++++++++++++++--
 include/linux/fanotify.h      |  9 ++++++---
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 89c19db4d45f..1aa23cefae5d 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -112,6 +112,7 @@ static u32 fanotify_group_event_mask(struct fsnotify_group *group,
 				     int data_type)
 {
 	__u32 marks_mask = 0, marks_ignored_mask = 0;
+	__u32 test_mask, user_mask = FANOTIFY_EVENT_TYPES;
 	const struct path *path = data;
 	struct fsnotify_mark *mark;
 	int type;
@@ -145,12 +146,38 @@ static u32 fanotify_group_event_mask(struct fsnotify_group *group,
 		marks_ignored_mask |= mark->ignored_mask;
 	}
 
+	test_mask = event_mask & marks_mask & ~marks_ignored_mask;
+
+	/*
+	 * dirent modification events (create/delete/move) do not carry the
+	 * child entry name/inode information. Instead, we report FAN_ONDIR
+	 * for mkdir/rmdir so user can differentiate them from creat/unlink.
+	 *
+	 * For backward compatibility and consistency, do not report FAN_ONDIR
+	 * to user in legacy fanotify mode (reporting fd) and report FAN_ONDIR
+	 * to user in FAN_REPORT_FID mode for all event types.
+	 */
+	if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
+		/* Do not report FAN_ONDIR without an event type */
+		BUILD_BUG_ON(FANOTIFY_EVENT_TYPES & FANOTIFY_EVENT_FLAGS);
+		if (!(test_mask & FANOTIFY_EVENT_TYPES))
+			return 0;
+
+		user_mask |= FAN_ONDIR;
+	}
+
+	/*
+	 * Unlike legacy fanotify events (open/access/close), dirent events
+	 * for subdir entries (mkdir/rmdir) will be reported regardless if
+	 * user requested FAN_ONDIR, but the FAN_ONDIR flag itself will only
+	 * be reported if the user asked for it.
+	 */
 	if (event_mask & FS_ISDIR &&
+	    !(event_mask & ALL_FSNOTIFY_DIRENT_EVENTS) &&
 	    !(marks_mask & FS_ISDIR & ~marks_ignored_mask))
 		return 0;
 
-	return event_mask & FANOTIFY_OUTGOING_EVENTS & marks_mask &
-		~marks_ignored_mask;
+	return test_mask & user_mask;
 }
 
 static int fanotify_encode_fid(struct fanotify_event *event,
diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index e9d45387089f..f5f86566c277 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -61,13 +61,16 @@
 #define FANOTIFY_PERM_EVENTS	(FAN_OPEN_PERM | FAN_ACCESS_PERM | \
 				 FAN_OPEN_EXEC_PERM)
 
+/* Events types that may be reported from vfs */
+#define FANOTIFY_EVENT_TYPES	(FANOTIFY_EVENTS | \
+				 FANOTIFY_PERM_EVENTS)
+
 /* Extra flags that may be reported with event or control handling of events */
 #define FANOTIFY_EVENT_FLAGS	(FAN_EVENT_ON_CHILD | FAN_ONDIR)
 
 /* Events that may be reported to user */
-#define FANOTIFY_OUTGOING_EVENTS	(FANOTIFY_EVENTS | \
-					 FANOTIFY_PERM_EVENTS | \
-					 FAN_Q_OVERFLOW)
+#define FANOTIFY_OUTGOING_EVENTS	(FANOTIFY_EVENT_TYPES | \
+					 FAN_Q_OVERFLOW | FAN_ONDIR)
 
 #define ALL_FANOTIFY_EVENT_BITS		(FANOTIFY_OUTGOING_EVENTS | \
 					 FANOTIFY_EVENT_FLAGS)
-- 
2.17.1