diff mbox series

[v2,2/2] fsnotify: consistent behavior for parent not watching children

Message ID 20220511190213.831646-3-amir73il@gmail.com (mailing list archive)
State New
Headers show
Series Fixes for fanotify parent dir ignore mask logic | expand

Commit Message

Amir Goldstein May 11, 2022, 7:02 p.m. UTC
The logic for handling events on child in groups that have a mark on
the parent inode, but without FS_EVENT_ON_CHILD flag in the mask is
duplicated in several places and inconsistent.

Move the logic into the preparation of mark type iterator, so that the
parent mark type will be excluded from all mark type iterations in that
case.

This results in several subtle changes of behavior, hopefully all
desired changes of behavior, for example:

- Group A has a mount mark with FS_MODIFY in mask
- Group A has a mark with ignore mask that does not survive FS_MODIFY
  and does not watch children on directory D.
- Group B has a mark with FS_MODIFY in mask that does watch children
  on directory D.
- FS_MODIFY event on file D/foo should not clear the ignore mask of
  group A, but before this change it does

And if group A ignore mask was set to survive FS_MODIFY:
- FS_MODIFY event on file D/foo should be reported to group A on account
  of the mount mark, but before this change it is wrongly ignored

Fixes: 2f02fd3fa13e ("fanotify: fix ignore mask logic for events on child and on dir")
Reported-by: Jan Kara <jack@suse.com>
Link: https://lore.kernel.org/linux-fsdevel/20220314113337.j7slrb5srxukztje@quack3.lan/
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/fanotify/fanotify.c | 10 +---------
 fs/notify/fsnotify.c          | 34 +++++++++++++++++++---------------
 2 files changed, 20 insertions(+), 24 deletions(-)

Comments

Amir Goldstein June 20, 2022, 2:16 p.m. UTC | #1
On Wed, May 11, 2022 at 10:02 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> The logic for handling events on child in groups that have a mark on
> the parent inode, but without FS_EVENT_ON_CHILD flag in the mask is
> duplicated in several places and inconsistent.
>
> Move the logic into the preparation of mark type iterator, so that the
> parent mark type will be excluded from all mark type iterations in that
> case.
>
> This results in several subtle changes of behavior, hopefully all
> desired changes of behavior, for example:
>
> - Group A has a mount mark with FS_MODIFY in mask
> - Group A has a mark with ignore mask that does not survive FS_MODIFY
>   and does not watch children on directory D.
> - Group B has a mark with FS_MODIFY in mask that does watch children
>   on directory D.
> - FS_MODIFY event on file D/foo should not clear the ignore mask of
>   group A, but before this change it does
>
> And if group A ignore mask was set to survive FS_MODIFY:
> - FS_MODIFY event on file D/foo should be reported to group A on account
>   of the mount mark, but before this change it is wrongly ignored
>
> Fixes: 2f02fd3fa13e ("fanotify: fix ignore mask logic for events on child and on dir")
> Reported-by: Jan Kara <jack@suse.com>
> Link: https://lore.kernel.org/linux-fsdevel/20220314113337.j7slrb5srxukztje@quack3.lan/
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---

Greg,

FYI, this needs the previous commit to apply to 5.18.y:

e730558adffb fsnotify: consistent behavior for parent not watching children
14362a254179 fsnotify: introduce mark type iterator

They won't apply to earlier versions and this is a fix for a very minor bug
that existed forever, so no need to bother.

Thanks,
Amir.
Greg KH June 20, 2022, 8:34 p.m. UTC | #2
On Mon, Jun 20, 2022 at 05:16:16PM +0300, Amir Goldstein wrote:
> On Wed, May 11, 2022 at 10:02 PM Amir Goldstein <amir73il@gmail.com> wrote:
> >
> > The logic for handling events on child in groups that have a mark on
> > the parent inode, but without FS_EVENT_ON_CHILD flag in the mask is
> > duplicated in several places and inconsistent.
> >
> > Move the logic into the preparation of mark type iterator, so that the
> > parent mark type will be excluded from all mark type iterations in that
> > case.
> >
> > This results in several subtle changes of behavior, hopefully all
> > desired changes of behavior, for example:
> >
> > - Group A has a mount mark with FS_MODIFY in mask
> > - Group A has a mark with ignore mask that does not survive FS_MODIFY
> >   and does not watch children on directory D.
> > - Group B has a mark with FS_MODIFY in mask that does watch children
> >   on directory D.
> > - FS_MODIFY event on file D/foo should not clear the ignore mask of
> >   group A, but before this change it does
> >
> > And if group A ignore mask was set to survive FS_MODIFY:
> > - FS_MODIFY event on file D/foo should be reported to group A on account
> >   of the mount mark, but before this change it is wrongly ignored
> >
> > Fixes: 2f02fd3fa13e ("fanotify: fix ignore mask logic for events on child and on dir")
> > Reported-by: Jan Kara <jack@suse.com>
> > Link: https://lore.kernel.org/linux-fsdevel/20220314113337.j7slrb5srxukztje@quack3.lan/
> > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > ---
> 
> Greg,
> 
> FYI, this needs the previous commit to apply to 5.18.y:

What is "this" here?  What git id?

> e730558adffb fsnotify: consistent behavior for parent not watching children
> 14362a254179 fsnotify: introduce mark type iterator
> 
> They won't apply to earlier versions and this is a fix for a very minor bug
> that existed forever, so no need to bother.

So what exactly needs to be applied in what order and to what trees?

confused,

greg k-h
Amir Goldstein June 21, 2022, 3:04 a.m. UTC | #3
On Mon, Jun 20, 2022 at 11:34 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Mon, Jun 20, 2022 at 05:16:16PM +0300, Amir Goldstein wrote:
> > On Wed, May 11, 2022 at 10:02 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > >
> > > The logic for handling events on child in groups that have a mark on
> > > the parent inode, but without FS_EVENT_ON_CHILD flag in the mask is
> > > duplicated in several places and inconsistent.
> > >
> > > Move the logic into the preparation of mark type iterator, so that the
> > > parent mark type will be excluded from all mark type iterations in that
> > > case.
> > >
> > > This results in several subtle changes of behavior, hopefully all
> > > desired changes of behavior, for example:
> > >
> > > - Group A has a mount mark with FS_MODIFY in mask
> > > - Group A has a mark with ignore mask that does not survive FS_MODIFY
> > >   and does not watch children on directory D.
> > > - Group B has a mark with FS_MODIFY in mask that does watch children
> > >   on directory D.
> > > - FS_MODIFY event on file D/foo should not clear the ignore mask of
> > >   group A, but before this change it does
> > >
> > > And if group A ignore mask was set to survive FS_MODIFY:
> > > - FS_MODIFY event on file D/foo should be reported to group A on account
> > >   of the mount mark, but before this change it is wrongly ignored
> > >
> > > Fixes: 2f02fd3fa13e ("fanotify: fix ignore mask logic for events on child and on dir")
> > > Reported-by: Jan Kara <jack@suse.com>
> > > Link: https://lore.kernel.org/linux-fsdevel/20220314113337.j7slrb5srxukztje@quack3.lan/
> > > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > > ---
> >
> > Greg,
> >
> > FYI, this needs the previous commit to apply to 5.18.y:
>
> What is "this" here?  What git id?

Sorry, this commit:

> > e730558adffb fsnotify: consistent behavior for parent not watching children

Needs this previous commit:

> > 14362a254179 fsnotify: introduce mark type iterator

> > They won't apply to earlier versions and this is a fix for a very minor bug
> > that existed forever, so no need to bother.
>
> So what exactly needs to be applied in what order and to what trees?
>

To apply to 5.18.y.

Don't bother trying to apply either to earlier trees.

Thanks,
Amir.
Greg KH June 23, 2022, 4:09 p.m. UTC | #4
On Tue, Jun 21, 2022 at 06:04:33AM +0300, Amir Goldstein wrote:
> On Mon, Jun 20, 2022 at 11:34 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Mon, Jun 20, 2022 at 05:16:16PM +0300, Amir Goldstein wrote:
> > > On Wed, May 11, 2022 at 10:02 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > > >
> > > > The logic for handling events on child in groups that have a mark on
> > > > the parent inode, but without FS_EVENT_ON_CHILD flag in the mask is
> > > > duplicated in several places and inconsistent.
> > > >
> > > > Move the logic into the preparation of mark type iterator, so that the
> > > > parent mark type will be excluded from all mark type iterations in that
> > > > case.
> > > >
> > > > This results in several subtle changes of behavior, hopefully all
> > > > desired changes of behavior, for example:
> > > >
> > > > - Group A has a mount mark with FS_MODIFY in mask
> > > > - Group A has a mark with ignore mask that does not survive FS_MODIFY
> > > >   and does not watch children on directory D.
> > > > - Group B has a mark with FS_MODIFY in mask that does watch children
> > > >   on directory D.
> > > > - FS_MODIFY event on file D/foo should not clear the ignore mask of
> > > >   group A, but before this change it does
> > > >
> > > > And if group A ignore mask was set to survive FS_MODIFY:
> > > > - FS_MODIFY event on file D/foo should be reported to group A on account
> > > >   of the mount mark, but before this change it is wrongly ignored
> > > >
> > > > Fixes: 2f02fd3fa13e ("fanotify: fix ignore mask logic for events on child and on dir")
> > > > Reported-by: Jan Kara <jack@suse.com>
> > > > Link: https://lore.kernel.org/linux-fsdevel/20220314113337.j7slrb5srxukztje@quack3.lan/
> > > > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > > > ---
> > >
> > > Greg,
> > >
> > > FYI, this needs the previous commit to apply to 5.18.y:
> >
> > What is "this" here?  What git id?
> 
> Sorry, this commit:
> 
> > > e730558adffb fsnotify: consistent behavior for parent not watching children
> 
> Needs this previous commit:
> 
> > > 14362a254179 fsnotify: introduce mark type iterator
> 
> > > They won't apply to earlier versions and this is a fix for a very minor bug
> > > that existed forever, so no need to bother.
> >
> > So what exactly needs to be applied in what order and to what trees?
> >
> 
> To apply to 5.18.y.

Now queued up, thanks.

> Don't bother trying to apply either to earlier trees.

So the Fixes: tag lied?  No wonder I was confused :)

thanks,

greg k-h
Amir Goldstein June 24, 2022, 8:41 a.m. UTC | #5
On Thu, Jun 23, 2022 at 7:09 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, Jun 21, 2022 at 06:04:33AM +0300, Amir Goldstein wrote:
> > On Mon, Jun 20, 2022 at 11:34 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > >
> > > On Mon, Jun 20, 2022 at 05:16:16PM +0300, Amir Goldstein wrote:
> > > > On Wed, May 11, 2022 at 10:02 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > > > >
> > > > > The logic for handling events on child in groups that have a mark on
> > > > > the parent inode, but without FS_EVENT_ON_CHILD flag in the mask is
> > > > > duplicated in several places and inconsistent.
> > > > >
> > > > > Move the logic into the preparation of mark type iterator, so that the
> > > > > parent mark type will be excluded from all mark type iterations in that
> > > > > case.
> > > > >
> > > > > This results in several subtle changes of behavior, hopefully all
> > > > > desired changes of behavior, for example:
> > > > >
> > > > > - Group A has a mount mark with FS_MODIFY in mask
> > > > > - Group A has a mark with ignore mask that does not survive FS_MODIFY
> > > > >   and does not watch children on directory D.
> > > > > - Group B has a mark with FS_MODIFY in mask that does watch children
> > > > >   on directory D.
> > > > > - FS_MODIFY event on file D/foo should not clear the ignore mask of
> > > > >   group A, but before this change it does
> > > > >
> > > > > And if group A ignore mask was set to survive FS_MODIFY:
> > > > > - FS_MODIFY event on file D/foo should be reported to group A on account
> > > > >   of the mount mark, but before this change it is wrongly ignored
> > > > >
> > > > > Fixes: 2f02fd3fa13e ("fanotify: fix ignore mask logic for events on child and on dir")
> > > > > Reported-by: Jan Kara <jack@suse.com>
> > > > > Link: https://lore.kernel.org/linux-fsdevel/20220314113337.j7slrb5srxukztje@quack3.lan/
> > > > > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > > > > ---
> > > >
> > > > Greg,
> > > >
> > > > FYI, this needs the previous commit to apply to 5.18.y:
> > >
> > > What is "this" here?  What git id?
> >
> > Sorry, this commit:
> >
> > > > e730558adffb fsnotify: consistent behavior for parent not watching children
> >
> > Needs this previous commit:
> >
> > > > 14362a254179 fsnotify: introduce mark type iterator
> >
> > > > They won't apply to earlier versions and this is a fix for a very minor bug
> > > > that existed forever, so no need to bother.
> > >
> > > So what exactly needs to be applied in what order and to what trees?
> > >
> >
> > To apply to 5.18.y.
>
> Now queued up, thanks.
>
> > Don't bother trying to apply either to earlier trees.
>
> So the Fixes: tag lied?  No wonder I was confused :)

No it hasn't lied.

The fix could be backported to an earlier kernel, but it is not trivial
and I don't think it is worth the effort, because the behavior of this
corner case was undefined for the entire lifetime of fanotify.

IOW, if stable scripts send me the message that the patch
does not apply cleanly, I won't be doing anything about it.

Furthermore, I instrumented the LTP regression test for this
bug with:

        if (tc->ignore && tst_kvercmp(5, 19, 0) < 0) {
                tst_res(TCONF, "ignored mask on parent dir has undefined "
                                "behavior on kernel < 5.19");
                return;
        }

So no one is going to be asking for this backport, unless they really
encounter the problem in real world use cases.

Thanks,
Amir.
diff mbox series

Patch

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 263d303d8f8f..4f897e109547 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -320,7 +320,7 @@  static u32 fanotify_group_event_mask(struct fsnotify_group *group,
 	}
 
 	fsnotify_foreach_iter_mark_type(iter_info, mark, type) {
-		/* Apply ignore mask regardless of ISDIR and ON_CHILD flags */
+		/* Apply ignore mask regardless of mark's ISDIR flag */
 		marks_ignored_mask |= mark->ignored_mask;
 
 		/*
@@ -330,14 +330,6 @@  static u32 fanotify_group_event_mask(struct fsnotify_group *group,
 		if (event_mask & FS_ISDIR && !(mark->mask & FS_ISDIR))
 			continue;
 
-		/*
-		 * If the event is on a child and this mark is on a parent not
-		 * watching children, don't send it!
-		 */
-		if (type == FSNOTIFY_ITER_TYPE_PARENT &&
-		    !(mark->mask & FS_EVENT_ON_CHILD))
-			continue;
-
 		marks_mask |= mark->mask;
 
 		/* Record the mark types of this group that matched the event */
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index c5bb2405ead3..2c9a13c31ac9 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -290,22 +290,15 @@  static int fsnotify_handle_event(struct fsnotify_group *group, __u32 mask,
 	}
 
 	if (parent_mark) {
-		/*
-		 * parent_mark indicates that the parent inode is watching
-		 * children and interested in this event, which is an event
-		 * possible on child. But is *this mark* watching children and
-		 * interested in this event?
-		 */
-		if (parent_mark->mask & FS_EVENT_ON_CHILD) {
-			ret = fsnotify_handle_inode_event(group, parent_mark, mask,
-							  data, data_type, dir, name, 0);
-			if (ret)
-				return ret;
-		}
-		if (!inode_mark)
-			return 0;
+		ret = fsnotify_handle_inode_event(group, parent_mark, mask,
+						  data, data_type, dir, name, 0);
+		if (ret)
+			return ret;
 	}
 
+	if (!inode_mark)
+		return 0;
+
 	if (mask & FS_EVENT_ON_CHILD) {
 		/*
 		 * Some events can be sent on both parent dir and child marks
@@ -422,8 +415,19 @@  static bool fsnotify_iter_select_report_types(
 	iter_info->report_mask = 0;
 	fsnotify_foreach_iter_type(type) {
 		mark = iter_info->marks[type];
-		if (mark && mark->group == iter_info->current_group)
+		if (mark && mark->group == iter_info->current_group) {
+			/*
+			 * FSNOTIFY_ITER_TYPE_PARENT indicates that this inode
+			 * is watching children and interested in this event,
+			 * which is an event possible on child.
+			 * But is *this mark* watching children?
+			 */
+			if (type == FSNOTIFY_ITER_TYPE_PARENT &&
+			    !(mark->mask & FS_EVENT_ON_CHILD))
+				continue;
+
 			fsnotify_iter_set_report_type(iter_info, type);
+		}
 	}
 
 	return true;