[PATCH v4 13/15] fanotify: support events with data type FSNOTIFY_EVENT_INODE

[Amir Goldstein <amir73il@gmail.com>]

When event data type is FSNOTIFY_EVENT_INODE, we don't have a refernece
to the mount, so we will not be able to open a file descriptor when user
reads the event. However, if the listener has enabled reporting file
identifier with the FAN_REPORT_FID init flag, we allow repoting those
events and we use an indentifier inode to encode fid.

The inode to use as indetifier when reporting fid depedns on the event.
For dirent modification events, we report the modified directory inode
and we report the "victim" inode otherwise.
For example:
FS_ATTRIB reports the child inode even if reported on a watched parent.
FS_CREATE reports the modified dir inode and not the created inode.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify.c      | 67 ++++++++++++++++++++----------
 fs/notify/fanotify/fanotify.h      |  2 +-
 fs/notify/fanotify/fanotify_user.c |  3 +-
 3 files changed, 48 insertions(+), 24 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 5a958b1d0cb6..5f157dee2089 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -96,7 +96,7 @@ static int fanotify_get_response(struct fsnotify_group *group,
 
 	pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
 		 group, event, ret);
-	
+
 	return ret;
 }
 
@@ -106,9 +106,10 @@ static int fanotify_get_response(struct fsnotify_group *group,
  * been included within the event mask, but have not been explicitly
  * requested by the user, will not be present in the returned mask.
  */
-static u32 fanotify_group_event_mask(struct fsnotify_iter_info *iter_info,
-				       u32 event_mask, const void *data,
-				       int data_type)
+static u32 fanotify_group_event_mask(struct fsnotify_group *group,
+				     struct fsnotify_iter_info *iter_info,
+				     u32 event_mask, const void *data,
+				     int data_type)
 {
 	__u32 marks_mask = 0, marks_ignored_mask = 0;
 	const struct path *path = data;
@@ -118,14 +119,14 @@ static u32 fanotify_group_event_mask(struct fsnotify_iter_info *iter_info,
 	pr_debug("%s: report_mask=%x mask=%x data=%p data_type=%d\n",
 		 __func__, iter_info->report_mask, event_mask, data, data_type);
 
-	/* If we don't have enough info to send an event to userspace say no */
-	if (data_type != FSNOTIFY_EVENT_PATH)
-		return 0;
-
-	/* Sorry, fanotify only gives a damn about files and dirs */
-	if (!d_is_reg(path->dentry) &&
-	    !d_can_lookup(path->dentry))
+	if (data_type == FSNOTIFY_EVENT_PATH) {
+		/* Path type events are only relevant for files and dirs */
+		if (!d_is_reg(path->dentry) && !d_can_lookup(path->dentry))
+			return 0;
+	} else if (!FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
+		/* Events without path data require FAN_REPORT_FID */
 		return 0;
+	}
 
 	fsnotify_foreach_obj_type(type) {
 		if (!fsnotify_iter_should_report_type(iter_info, type))
@@ -153,7 +154,7 @@ static u32 fanotify_group_event_mask(struct fsnotify_iter_info *iter_info,
 }
 
 static int fanotify_encode_fid(struct fanotify_event *event,
-			       const struct path *path, gfp_t gfp,
+			       struct inode *inode, gfp_t gfp,
 			       __kernel_fsid_t *fsid)
 {
 	struct fanotify_fid *fid = &event->fid;
@@ -166,7 +167,7 @@ static int fanotify_encode_fid(struct fanotify_event *event,
 	fid->ext_fh = NULL;
 	dwords = 0;
 	err = -ENOENT;
-	type = exportfs_encode_fh(path->dentry, NULL, &dwords,  0);
+	type = exportfs_encode_inode_fh(inode, NULL, &dwords,  NULL);
 	if (!dwords)
 		goto out_err;
 
@@ -179,8 +180,8 @@ static int fanotify_encode_fid(struct fanotify_event *event,
 			goto out_err;
 	}
 
-	type = exportfs_encode_fh(path->dentry, fanotify_fid_fh(fid, bytes),
-				  &dwords,  0);
+	type = exportfs_encode_inode_fh(inode, fanotify_fid_fh(fid, bytes),
+					&dwords,  NULL);
 	err = -EINVAL;
 	if (!type || type == FILEID_INVALID || bytes != dwords << 2)
 		goto out_err;
@@ -201,13 +202,34 @@ static int fanotify_encode_fid(struct fanotify_event *event,
 	return FILEID_INVALID;
 }
 
+/*
+ * The inode to use as indetifier when reporting fid depedns on the event.
+ * Report the modified directory inode on dirent modification events.
+ * Report the "victim" inode otherwise.
+ * For example:
+ * FS_ATTRIB reports the child inode even if reported on a watched parent.
+ * FS_CREATE reports the modified dir inode and not the created inode.
+ */
+static struct inode *fanotify_report_id(struct inode *to_tell, u32 event_mask,
+					const void *data, int data_type)
+{
+	if (event_mask & ALL_FSNOTIFY_DIRENT_EVENTS)
+		return to_tell;
+	else if (data_type == FSNOTIFY_EVENT_INODE)
+		return (struct inode *)data;
+	else if (data_type == FSNOTIFY_EVENT_PATH)
+		return d_inode(((struct path *)data)->dentry);
+	return NULL;
+}
+
 struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 					    struct inode *inode, u32 mask,
-					    const struct path *path,
+					    const void *data, int data_type,
 					    __kernel_fsid_t *fsid)
 {
 	struct fanotify_event *event = NULL;
 	gfp_t gfp = GFP_KERNEL_ACCOUNT;
+	struct inode *id = fanotify_report_id(inode, mask, data, data_type);
 
 	/*
 	 * For queues with unlimited length lost events are not expected and
@@ -241,12 +263,12 @@ init: __maybe_unused
 	else
 		event->pid = get_pid(task_tgid(current));
 	event->fh_len = 0;
-	if (path && FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
+	if (id && FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
 		/* Report the event without a file identifier on encode error */
-		event->fh_type = fanotify_encode_fid(event, path, gfp, fsid);
-	} else if (path) {
+		event->fh_type = fanotify_encode_fid(event, id, gfp, fsid);
+	} else if (data_type == FSNOTIFY_EVENT_PATH) {
 		event->fh_type = 0;
-		event->path = *path;
+		event->path = *((struct path *)data);
 		path_get(&event->path);
 	} else {
 		event->fh_type = FILEID_INVALID;
@@ -306,7 +328,8 @@ static int fanotify_handle_event(struct fsnotify_group *group,
 
 	BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 12);
 
-	mask = fanotify_group_event_mask(iter_info, mask, data, data_type);
+	mask = fanotify_group_event_mask(group, iter_info, mask, data,
+					 data_type);
 	if (!mask)
 		return 0;
 
@@ -325,7 +348,7 @@ static int fanotify_handle_event(struct fsnotify_group *group,
 	if (FAN_GROUP_FLAG(group, FAN_REPORT_FID))
 		fsid = fanotify_get_fsid(iter_info, &__fsid);
 
-	event = fanotify_alloc_event(group, inode, mask, data, fsid);
+	event = fanotify_alloc_event(group, inode, mask, data, data_type, fsid);
 	ret = -ENOMEM;
 	if (unlikely(!event)) {
 		/*
diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index 06b93cf227a2..3fd74949a26d 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -136,5 +136,5 @@ static inline struct fanotify_event *FANOTIFY_E(struct fsnotify_event *fse)
 
 struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 					    struct inode *inode, u32 mask,
-					    const struct path *path,
+					    const void *data, int data_type,
 					    __kernel_fsid_t *fsid);
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 8ecd9db8931c..8bbcf6157927 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -792,7 +792,8 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
 	atomic_inc(&user->fanotify_listeners);
 	group->memcg = get_mem_cgroup_from_mm(current->mm);
 
-	oevent = fanotify_alloc_event(group, NULL, FS_Q_OVERFLOW, NULL, NULL);
+	oevent = fanotify_alloc_event(group, NULL, FS_Q_OVERFLOW, NULL,
+				      FSNOTIFY_EVENT_NONE, NULL);
 	if (unlikely(!oevent)) {
 		fd = -ENOMEM;
 		goto out_destroy_group;
-- 
2.17.1