[PATCH 7/9] fsnotify: fix merge with parent mark masks

[Amir Goldstein <amir73il@gmail.com>]

When reporting event with parent/name info, we should not merge
parent's mark mask and ignore mask, unless the parent has the flag
FS_EVENT_ON_CHILD in the mask.

Therefore, in fsnotify_parent(), set the FS_EVENT_ON_CHILD flag in event
mask only if parent is watching and use this flag to decide if the
parent mark masks should be merged with child/sb/mount marks.

After this change, even groups that do not subscribe to events on
children could get an event with mark iterator type TYPE_CHILD and
without mark iterator type TYPE_INODE if fanotify has marks on the same
objects.

dnotify and inotify event handlers can already cope with that situation.
audit does not subscribe to events that are possible on child, so won't
get to this situation. nfsd does not access the marks iterator from its
event handler at the moment, so it is not affected.

This is a bit too fragile, so we should prepare all groups to cope with
mark type TYPE_CHILD preferably using a generic helper.

Link: https://lore.kernel.org/linux-fsdevel/20200716223441.GA5085@quack2.suse.cz/
Fixes: ecf13b5f8fd6 ("fsnotify: send event with parent/name info to sb/mount/non-dir marks")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify.c |  2 +-
 fs/notify/fsnotify.c          | 20 +++++++++++++-------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 03e3dce2a97c..3336157d895d 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -538,7 +538,7 @@ static struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 		 * in addition to reporting the parent fid and maybe child name.
 		 */
 		if ((fid_mode & FAN_REPORT_FID) &&
-		    (mask & FAN_EVENT_ON_CHILD) && !(mask & FAN_ONDIR))
+		    id != dirid && !(mask & FAN_ONDIR))
 			child = id;
 
 		id = dirid;
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 3b805e05c02d..494d5d70323f 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -215,7 +215,8 @@ int __fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data,
 		/* Notify both parent and child with child name info */
 		take_dentry_name_snapshot(&name, dentry);
 		file_name = &name.name;
-		mask |= FS_EVENT_ON_CHILD;
+		if (parent_watched)
+			mask |= FS_EVENT_ON_CHILD;
 	}
 
 notify:
@@ -391,8 +392,8 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 		inode = dir;
 	} else if (mask & FS_EVENT_ON_CHILD) {
 		/*
-		 * Event on child - report on TYPE_INODE to dir
-		 * and on TYPE_CHILD to child.
+		 * Event on child - report on TYPE_INODE to dir if it is
+		 * watching children and on TYPE_CHILD to child.
 		 */
 		child = inode;
 		inode = dir;
@@ -406,14 +407,17 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 	 * SRCU because we have no references to any objects and do not
 	 * need SRCU to keep them "alive".
 	 */
-	if (!inode->i_fsnotify_marks && !sb->s_fsnotify_marks &&
+	if (!sb->s_fsnotify_marks &&
 	    (!mnt || !mnt->mnt_fsnotify_marks) &&
+	    (!inode || !inode->i_fsnotify_marks) &&
 	    (!child || !child->i_fsnotify_marks))
 		return 0;
 
-	marks_mask = inode->i_fsnotify_mask | sb->s_fsnotify_mask;
+	marks_mask = sb->s_fsnotify_mask;
 	if (mnt)
 		marks_mask |= mnt->mnt_fsnotify_mask;
+	if (inode)
+		marks_mask |= inode->i_fsnotify_mask;
 	if (child)
 		marks_mask |= child->i_fsnotify_mask;
 
@@ -428,14 +432,16 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 
 	iter_info.srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
 
-	iter_info.marks[FSNOTIFY_OBJ_TYPE_INODE] =
-		fsnotify_first_mark(&inode->i_fsnotify_marks);
 	iter_info.marks[FSNOTIFY_OBJ_TYPE_SB] =
 		fsnotify_first_mark(&sb->s_fsnotify_marks);
 	if (mnt) {
 		iter_info.marks[FSNOTIFY_OBJ_TYPE_VFSMOUNT] =
 			fsnotify_first_mark(&mnt->mnt_fsnotify_marks);
 	}
+	if (inode) {
+		iter_info.marks[FSNOTIFY_OBJ_TYPE_INODE] =
+			fsnotify_first_mark(&inode->i_fsnotify_marks);
+	}
 	if (child) {
 		iter_info.marks[FSNOTIFY_OBJ_TYPE_CHILD] =
 			fsnotify_first_mark(&child->i_fsnotify_marks);
-- 
2.17.1