[PATCH 5.9 247/252] fanotify: fix logic of reporting name info with watched parent

Greg Kroah-Hartman
2020-11-23T12:59:42Z

From: Amir Goldstein <amir73il@gmail.com>

commit 7372e79c9eb9d7034e498721eb2861ae4fdbc618 upstream.

The victim inode's parent and name info is required when an event
needs to be delivered to a group interested in filename info OR
when the inode's parent is interested in an event on its children.

Let us call the first condition 'parent_needed' and the second
condition 'parent_interested'.

In fsnotify_parent(), the condition where the inode's parent is
interested in some events on its children, but not necessarily
interested the specific event is called 'parent_watched'.

fsnotify_parent() tests the condition (!parent_watched && !parent_needed)
for sending the event without parent and name info, which is correct.

It then wrongly assumes that parent_watched implies !parent_needed
and tests the condition (parent_watched && !parent_interested)
for sending the event without parent and name info, which is wrong,
because parent may still be needed by some group.

For example, after initializing a group with FAN_REPORT_DFID_NAME and
adding a FAN_MARK_MOUNT with FAN_OPEN mask, open events on non-directory
children of "testdir" are delivered with file name info.

After adding another mark to the same group on the parent "testdir"
with FAN_CLOSE|FAN_EVENT_ON_CHILD mask, open events on non-directory
children of "testdir" are no longer delivered with file name info.

Fix the logic and use auxiliary variables to clarify the conditions.

Fixes: 9b93f33105f5 ("fsnotify: send event with parent/name info to sb/mount/non-dir marks")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20201108105906.8493-1-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/notify/fsnotify.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -178,6 +178,7 @@ int __fsnotify_parent(struct dentry *den
struct inode *inode = d_inode(dentry);
struct dentry *parent;
bool parent_watched = dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED;
+ bool parent_needed, parent_interested;
__u32 p_mask;
struct inode *p_inode = NULL;
struct name_snapshot name;
@@ -193,7 +194,8 @@ int __fsnotify_parent(struct dentry *den
return 0;

parent = NULL;
- if (!parent_watched && !fsnotify_event_needs_parent(inode, mnt, mask))
+ parent_needed = fsnotify_event_needs_parent(inode, mnt, mask);
+ if (!parent_watched && !parent_needed)
goto notify;

/* Does parent inode care about events on children? */
@@ -205,17 +207,17 @@ int __fsnotify_parent(struct dentry *den

/*
* Include parent/name in notification either if some notification
- * groups require parent info (!parent_watched case) or the parent is
- * interested in this event.
+ * groups require parent info or the parent is interested in this event.
*/
- if (!parent_watched || (mask & p_mask & ALL_FSNOTIFY_EVENTS)) {
+ parent_interested = mask & p_mask & ALL_FSNOTIFY_EVENTS;
+ if (parent_needed || parent_interested) {
/* When notifying parent, child should be passed as data */
WARN_ON_ONCE(inode != fsnotify_data_inode(data, data_type));

/* Notify both parent and child with child name info */
take_dentry_name_snapshot(&name, dentry);
file_name = &name.name;
- if (parent_watched)
+ if (parent_interested)
mask |= FS_EVENT_ON_CHILD;
}