This fanotify_init() flag is similar to FAN_REPORT_MNT, but instead of
enabling the legacy FAN_MNT_* events, it enabled the new FAN_NS_MNT_*
events which also report the watcher type bits in event->mask.

FAN_REPORT_MNT and FAN_REPORT_MNTID are mutually exclusive and therefore
the group accepts either the legacy FAN_MNT_* events or the new
FAN_NS_MNT_* events in fanotify_mark().

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify_user.c | 21 ++++++++++++++-------
 include/linux/fanotify.h           |  9 +++++++--
 include/uapi/linux/fanotify.h      |  3 ++-
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 76bb2574c8239..57cae2b3c96f8 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -852,6 +852,9 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
 	metadata.vers = FANOTIFY_METADATA_VERSION;
 	metadata.reserved = 0;
 	metadata.mask = fanotify_group_outgoing_events(group, event->mask);
+	/* Report watcher type part of the event mask */
+	if (FAN_GROUP_FLAG(group, FANOTIFY_REPORT_TYPE))
+		metadata.mask |= (u64)group->type << FAN_EVENT_TYPE_SHIFT;
 	metadata.pid = pid_vnr(event->pid);
 	/*
 	 * For an unprivileged listener, event->pid can be used to identify the
@@ -1669,6 +1672,9 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
 			return -EINVAL;
 		if (flags & (FANOTIFY_FID_BITS | FAN_REPORT_FD_ERROR))
 			return -EINVAL;
+		/* The old and new mount event modes are mutually exclusive */
+		if ((flags & FAN_REPORT_MNT) && (flags & FAN_REPORT_MNTID))
+			return -EINVAL;
 	}
 
 	if (event_f_flags & ~FANOTIFY_INIT_ALL_EVENT_F_BITS)
@@ -1913,6 +1919,10 @@ static bool fanotify_is_valid_mask(struct fsnotify_group *group, int mark_type,
 	BUILD_BUG_ON(FANOTIFY_EVENTS_ON_FILESYSTEM & FANOTIFY_EVENT_FLAGS);
 	BUILD_BUG_ON(FANOTIFY_EVENTS_ON_NAMESPACE & FANOTIFY_EVENT_FLAGS);
 
+	/* Only allow high bits in mask when reporting them in event->mask */
+	if (!FAN_GROUP_FLAG(group, FANOTIFY_REPORT_TYPE) && fan_mask.type)
+		return false;
+
 	switch (group->type) {
 	case FSNOTIFY_GROUP_TYPE_FILESYSTEM:
 		valid_mask = FANOTIFY_EVENTS_ON_FILESYSTEM |
@@ -1923,10 +1933,11 @@ static bool fanotify_is_valid_mask(struct fsnotify_group *group, int mark_type,
 	case FSNOTIFY_GROUP_TYPE_NAMESPACE:
 		/* Only report mount events on mntns mark */
 		if (mark_type == FAN_MARK_MNTNS &&
-		    FAN_GROUP_FLAG(group, FAN_REPORT_MNT))
+		    FAN_GROUP_FLAG(group, FANOTIFY_MNT_MODES))
 			valid_mask = FANOTIFY_MOUNT_EVENTS;
 		/* Classify the legacy mount events as namespace events */
-		if (fan_mask.mask & (FAN_MNT_ATTACH | FAN_MNT_DETACH))
+		if (fan_mask.mask & (FAN_MNT_ATTACH | FAN_MNT_DETACH) &&
+		    FAN_GROUP_FLAG(group, FAN_REPORT_MNT))
 			fan_mask.type = FSNOTIFY_GROUP_TYPE_NAMESPACE;
 		break;
 	}
@@ -1963,10 +1974,6 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 __mask,
 	if (ret)
 		return ret;
 
-	/* we only use the lower 32 bits as of right now. */
-	if (fan_mask.type)
-		return -EINVAL;
-
 	if (flags & ~FANOTIFY_MARK_FLAGS)
 		return -EINVAL;
 
@@ -2251,7 +2258,7 @@ static int __init fanotify_user_setup(void)
 				     FANOTIFY_DEFAULT_MAX_USER_MARKS);
 
 	BUILD_BUG_ON(FANOTIFY_INIT_FLAGS & FANOTIFY_INTERNAL_GROUP_FLAGS);
-	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 14);
+	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 15);
 	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 11);
 
 	fanotify_mark_cache = KMEM_CACHE(fanotify_mark,
diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index 8679f63fd7c97..23c691031cce3 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -25,12 +25,17 @@
 
 #define FANOTIFY_FID_BITS	(FAN_REPORT_DFID_NAME_TARGET)
 
+#define FANOTIFY_MNT_MODES	(FAN_REPORT_MNT | FAN_REPORT_MNTID)
+
+/* fanotify_init() flags that report watcher type in event mask */
+#define FANOTIFY_REPORT_TYPE	(FAN_REPORT_MNTID)
+
 /* fanotify_init() flags related to information reported with events */
 #define FANOTIFY_INFO_MODES	(FANOTIFY_FID_BITS | FAN_REPORT_PIDFD | \
-				 FAN_REPORT_MNT)
+				 FANOTIFY_MNT_MODES)
 
 /* fanotify_init() flags that create a namespace watcher */
-#define FANOTIFY_NAMESPACE_INIT_FLAGS	(FAN_REPORT_MNT)
+#define FANOTIFY_NAMESPACE_INIT_FLAGS	(FANOTIFY_MNT_MODES)
 
 /*
  * fanotify_init() flags that require CAP_SYS_ADMIN.
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index b399dd3887299..0744b6770b43d 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -90,7 +90,8 @@
 #define FAN_REPORT_NAME		0x00000800	/* Report events with name */
 #define FAN_REPORT_TARGET_FID	0x00001000	/* Report dirent target id  */
 #define FAN_REPORT_FD_ERROR	0x00002000	/* event->fd can report error */
-#define FAN_REPORT_MNT		0x00004000	/* Report mount events */
+#define FAN_REPORT_MNT		0x00004000	/* Report FAN_MNT_ events */
+#define FAN_REPORT_MNTID	0x00008000	/* Report FAN_NS_MNT_ events */
 
 /* Convenience macro - FAN_REPORT_NAME requires FAN_REPORT_DIR_FID */
 #define FAN_REPORT_DFID_NAME	(FAN_REPORT_DIR_FID | FAN_REPORT_NAME)
-- 
2.55.0