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Commit e0873344 authored by Eric Paris's avatar Eric Paris
Browse files

inotify: race use after free/double free in inotify inode marks 



There is a race in the inotify add/rm watch code.  A task can find and
remove a mark which doesn't have all of it's references.  This can
result in a use after free/double free situation.

Task A					Task B
------------				-----------
inotify_new_watch()
 allocate a mark (refcnt == 1)
 add it to the idr
					inotify_rm_watch()
					 inotify_remove_from_idr()
					  fsnotify_put_mark()
					      refcnt hits 0, free
 take reference because we are on idr
 [at this point it is a use after free]
 [time goes on]
 refcnt may hit 0 again, double free

The fix is to take the reference BEFORE the object can be found in the
idr.

Signed-off-by: default avatarEric Paris <eparis@redhat.com>
Cc: <stable@kernel.org>
parent 3dbc6fb6

fs/notify/inotify/inotify_user.c

+6 −3
Original line number Diff line number Diff line
@@ -546,21 +546,24 @@ static int inotify_new_watch(struct fsnotify_group *group, 
	if (unlikely(!idr_pre_get(&group->inotify_data.idr, GFP_KERNEL)))

		goto out_err;



	/* we are putting the mark on the idr, take a reference */

	fsnotify_get_mark(&tmp_ientry->fsn_entry);



	spin_lock(&group->inotify_data.idr_lock);

	ret = idr_get_new_above(&group->inotify_data.idr, &tmp_ientry->fsn_entry,

				group->inotify_data.last_wd+1,

				&tmp_ientry->wd);

	spin_unlock(&group->inotify_data.idr_lock);

	if (ret) {

		/* we didn't get on the idr, drop the idr reference */

		fsnotify_put_mark(&tmp_ientry->fsn_entry);



		/* idr was out of memory allocate and try again */

		if (ret == -EAGAIN)

			goto retry;

		goto out_err;

	}



	/* we put the mark on the idr, take a reference */

	fsnotify_get_mark(&tmp_ientry->fsn_entry);



	/* we are on the idr, now get on the inode */

	ret = fsnotify_add_mark(&tmp_ientry->fsn_entry, group, inode);

	if (ret) {