[PATCH v2 5/9] fanotify: copy event fid info to user

[Amir Goldstein <amir73il@xxxxxxxxx>]

If group requested FAN_REPORT_FID and event has file identifier
copy that information to user reading the event after reading
event metadata.
metadata->event_len includes the length of the fid information.

Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
 fs/notify/fanotify/fanotify.h      |  3 ++
 fs/notify/fanotify/fanotify_user.c | 72 +++++++++++++++++++++++++++---
 2 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index d6ed31134321..26752d2f2bd6 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -10,6 +10,9 @@ extern struct kmem_cache *fanotify_perm_event_cachep;
 /* The size of the variable length buffer storing fsid and file handle */
 #define FANOTIFY_FID_LEN(handle_bytes)	\
 	(sizeof(struct fanotify_event_fid) + (handle_bytes))
+#define FANOTIFY_FID_INFO_LEN(event)	\
+	(sizeof(struct fanotify_event_info) + \
+	FANOTIFY_FID_LEN((event)->info.fid->handle_bytes))
 
 struct fanotify_info {
 	struct fanotify_event_fid *fid;
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 29f61060af66..7e38d7a1854b 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -47,6 +47,16 @@ struct kmem_cache *fanotify_mark_cache __read_mostly;
 struct kmem_cache *fanotify_event_cachep __read_mostly;
 struct kmem_cache *fanotify_perm_event_cachep __read_mostly;
 
+static int round_event_fid_len(struct fsnotify_event *fsn_event)
+{
+	struct fanotify_event *event = FANOTIFY_E(fsn_event);
+
+	if (!FANOTIFY_HAS_FID(event))
+		return 0;
+
+	return roundup(FANOTIFY_FID_INFO_LEN(event), FAN_EVENT_METADATA_LEN);
+}
+
 /*
  * Get an fsnotify notification event if one exists and is small
  * enough to fit in "count". Return an error pointer if the count
@@ -57,6 +67,9 @@ struct kmem_cache *fanotify_perm_event_cachep __read_mostly;
 static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
 					    size_t count)
 {
+	size_t event_size = FAN_EVENT_METADATA_LEN;
+	struct fsnotify_event *event;
+
 	assert_spin_locked(&group->notification_lock);
 
 	pr_debug("%s: group=%p count=%zd\n", __func__, group, count);
@@ -64,11 +77,18 @@ static struct fsnotify_event *get_one_event(struct fsnotify_group *group,
 	if (fsnotify_notify_queue_is_empty(group))
 		return NULL;
 
-	if (FAN_EVENT_METADATA_LEN > count)
+	if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
+		event = fsnotify_peek_first_event(group);
+		event_size += round_event_fid_len(event);
+	}
+
+	if (event_size > count)
 		return ERR_PTR(-EINVAL);
 
-	/* held the notification_lock the whole time, so this is the
-	 * same event we peeked above */
+	/*
+	 * Held the notification_lock the whole time, so this is the
+	 * same event we peeked above
+	 */
 	return fsnotify_remove_first_event(group);
 }
 
@@ -129,7 +149,7 @@ static int fill_event_metadata(struct fsnotify_group *group,
 		 group, metadata, fsn_event);
 
 	*file = NULL;
-	event = container_of(fsn_event, struct fanotify_event, fse);
+	event = FANOTIFY_E(fsn_event);
 	metadata->event_len = FAN_EVENT_METADATA_LEN;
 	metadata->metadata_len = FAN_EVENT_METADATA_LEN;
 	metadata->vers = FANOTIFY_METADATA_VERSION;
@@ -139,6 +159,7 @@ static int fill_event_metadata(struct fsnotify_group *group,
 	if (FAN_GROUP_FLAG(group, FAN_REPORT_FID) ||
 	    unlikely(fsn_event->mask & FAN_Q_OVERFLOW)) {
 		metadata->fd = FAN_NOFD;
+		metadata->event_len += round_event_fid_len(fsn_event);
 	} else {
 		metadata->fd = create_fd(group, event, file);
 		if (metadata->fd < 0)
@@ -208,6 +229,38 @@ static int process_access_response(struct fsnotify_group *group,
 	return 0;
 }
 
+static int copy_fid_to_user(struct fsnotify_event *fsn_event, char __user *buf)
+{
+	struct fanotify_event *event = FANOTIFY_E(fsn_event);
+	struct fanotify_event_info ei;
+	size_t fid_len;
+	size_t pad_len = round_event_fid_len(fsn_event);
+
+	if (!pad_len)
+		return 0;
+
+	/* Copy event info header followed by fid buffer */
+	fid_len = FANOTIFY_FID_INFO_LEN(event);
+	pad_len -= fid_len;
+	ei.info_type = FAN_EVENT_INFO_TYPE_FID;
+	ei.reserved = 0;
+	ei.info_len = fid_len;
+	if (copy_to_user(buf, &ei, sizeof(ei)))
+		return -EFAULT;
+
+	buf += sizeof(ei);
+	fid_len -= sizeof(ei);
+	if (copy_to_user(buf, event->info.fid, fid_len))
+		return -EFAULT;
+
+	/* Pad with 0's */
+	buf += fid_len;
+	if (pad_len && clear_user(buf, pad_len))
+		return -EFAULT;
+
+	return 0;
+}
+
 static ssize_t copy_event_to_user(struct fsnotify_group *group,
 				  struct fsnotify_event *event,
 				  char __user *buf)
@@ -224,15 +277,20 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
 
 	fd = fanotify_event_metadata.fd;
 	ret = -EFAULT;
-	if (copy_to_user(buf, &fanotify_event_metadata,
-			 fanotify_event_metadata.event_len))
+	if (copy_to_user(buf, &fanotify_event_metadata, FAN_EVENT_METADATA_LEN))
 		goto out_close_fd;
 
 	if (fanotify_is_perm_event(event->mask))
 		FANOTIFY_PE(event)->fd = fd;
 
-	if (fd != FAN_NOFD)
+	if (fd != FAN_NOFD) {
 		fd_install(fd, f);
+	} else if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
+		ret = copy_fid_to_user(event, buf + FAN_EVENT_METADATA_LEN);
+		if (ret < 0)
+			return ret;
+	}
+
 	return fanotify_event_metadata.event_len;
 
 out_close_fd:
-- 
2.17.1