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Message-ID: <1438876592.12629.7.camel@fourier>
Date: Thu, 06 Aug 2015 08:56:32 -0700
From: Kamal Mostafa <kamal@...onical.com>
To: Jan Kara <jack@...e.cz>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
kernel-team@...ts.ubuntu.com,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 3.19.y-ckt 096/107] fsnotify: fix oops in
fsnotify_clear_marks_by_group_flags()
On Thu, 2015-08-06 at 17:12 +0200, Jan Kara wrote:
> On Wed 05-08-15 14:49:28, Kamal Mostafa wrote:
> > 3.19.8-ckt5 -stable review patch. If anyone has any objections, please let me know.
>
> The patch was later reverted so please don't push it to stable.
>
> Honza
Thanks very much Jan. Dropped from 3.19-stable.
-Kamal
> > ------------------
> >
> > From: Jan Kara <jack@...e.cz>
> >
> > commit a2673b6e040663bf16a552f8619e6bde9f4b9acf upstream.
> >
> > fsnotify_clear_marks_by_group_flags() can race with
> > fsnotify_destroy_marks() so when fsnotify_destroy_mark_locked() drops
> > mark_mutex, a mark from the list iterated by
> > fsnotify_clear_marks_by_group_flags() can be freed and we dereference free
> > memory in the loop there.
> >
> > Fix the problem by keeping mark_mutex held in
> > fsnotify_destroy_mark_locked(). The reason why we drop that mutex is that
> > we need to call a ->freeing_mark() callback which may acquire mark_mutex
> > again. To avoid this and similar lock inversion issues, we move the call
> > to ->freeing_mark() callback to the kthread destroying the mark.
> >
> > Signed-off-by: Jan Kara <jack@...e.cz>
> > Reported-by: Ashish Sangwan <a.sangwan@...sung.com>
> > Suggested-by: Lino Sanfilippo <LinoSanfilippo@....de>
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> > Signed-off-by: Kamal Mostafa <kamal@...onical.com>
> > ---
> > fs/notify/mark.c | 34 ++++++++++++++--------------------
> > 1 file changed, 14 insertions(+), 20 deletions(-)
> >
> > diff --git a/fs/notify/mark.c b/fs/notify/mark.c
> > index 92e48c7..3e594ce4 100644
> > --- a/fs/notify/mark.c
> > +++ b/fs/notify/mark.c
> > @@ -152,31 +152,15 @@ void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
> > BUG();
> >
> > list_del_init(&mark->g_list);
> > -
> > spin_unlock(&mark->lock);
> >
> > if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
> > iput(inode);
> > - /* release lock temporarily */
> > - mutex_unlock(&group->mark_mutex);
> >
> > spin_lock(&destroy_lock);
> > list_add(&mark->g_list, &destroy_list);
> > spin_unlock(&destroy_lock);
> > wake_up(&destroy_waitq);
> > - /*
> > - * We don't necessarily have a ref on mark from caller so the above destroy
> > - * may have actually freed it, unless this group provides a 'freeing_mark'
> > - * function which must be holding a reference.
> > - */
> > -
> > - /*
> > - * Some groups like to know that marks are being freed. This is a
> > - * callback to the group function to let it know that this mark
> > - * is being freed.
> > - */
> > - if (group->ops->freeing_mark)
> > - group->ops->freeing_mark(mark, group);
> >
> > /*
> > * __fsnotify_update_child_dentry_flags(inode);
> > @@ -191,8 +175,6 @@ void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
> > */
> >
> > atomic_dec(&group->num_marks);
> > -
> > - mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
> > }
> >
> > void fsnotify_destroy_mark(struct fsnotify_mark *mark,
> > @@ -205,7 +187,10 @@ void fsnotify_destroy_mark(struct fsnotify_mark *mark,
> >
> > /*
> > * Destroy all marks in the given list. The marks must be already detached from
> > - * the original inode / vfsmount.
> > + * the original inode / vfsmount. Note that we can race with
> > + * fsnotify_clear_marks_by_group_flags(). However we hold a reference to each
> > + * mark so they won't get freed from under us and nobody else touches our
> > + * free_list list_head.
> > */
> > void fsnotify_destroy_marks(struct list_head *to_free)
> > {
> > @@ -406,7 +391,7 @@ struct fsnotify_mark *fsnotify_find_mark(struct hlist_head *head,
> > }
> >
> > /*
> > - * clear any marks in a group in which mark->flags & flags is true
> > + * Clear any marks in a group in which mark->flags & flags is true.
> > */
> > void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
> > unsigned int flags)
> > @@ -460,6 +445,7 @@ static int fsnotify_mark_destroy(void *ignored)
> > {
> > struct fsnotify_mark *mark, *next;
> > struct list_head private_destroy_list;
> > + struct fsnotify_group *group;
> >
> > for (;;) {
> > spin_lock(&destroy_lock);
> > @@ -471,6 +457,14 @@ static int fsnotify_mark_destroy(void *ignored)
> >
> > list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
> > list_del_init(&mark->g_list);
> > + group = mark->group;
> > + /*
> > + * Some groups like to know that marks are being freed.
> > + * This is a callback to the group function to let it
> > + * know that this mark is being freed.
> > + */
> > + if (group && group->ops->freeing_mark)
> > + group->ops->freeing_mark(mark, group);
> > fsnotify_put_mark(mark);
> > }
> >
> > --
> > 1.9.1
> >
--
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