[PATCH 05/22] audit: Fix sleep in atomic

[Jan Kara]

On Thu 22-12-16 18:18:36, Paul Moore wrote:
> On Thu, Dec 22, 2016 at 4:15 AM, Jan Kara <jack at suse.cz> wrote:
> > Audit tree code was happily adding new notification marks while holding
> > spinlocks. Since fsnotify_add_mark() acquires group->mark_mutex this can
> > lead to sleeping while holding a spinlock, deadlocks due to lock
> > inversion, and probably other fun. Fix the problem by acquiring
> > group->mark_mutex earlier.
> >
> > CC: Paul Moore <paul at paul-moore.com>
> > Signed-off-by: Jan Kara <jack at suse.cz>
> > ---
> >  kernel/audit_tree.c | 13 +++++++++++--
> >  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> [SIDE NOTE: this patch explains your comments and my earlier concern
> about the locked/unlocked variants of fsnotify_add_mark() in
> untag_chunk()]
> 
> Ouch.  Thanks for catching this ... what is your goal with these
> patches, are you targeting this as a fix during the v4.10-rcX cycle?
> If not, any objections if I pull this patch into the audit tree and
> send this to Linus during the v4.10-rcX cycle (assuming it passes
> testing, yadda yadda)?

Sure, go ahead. I plan these patches for the next merge window. So I can
rebase the series once you merge audit fixes...

								Honza
> 
> 
> > diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> > index f3130eb0a4bd..156b6a93f4fc 100644
> > --- a/kernel/audit_tree.c
> > +++ b/kernel/audit_tree.c
> > @@ -231,6 +231,7 @@ static void untag_chunk(struct node *p)
> >         if (size)
> >                 new = alloc_chunk(size);
> >
> > +       mutex_lock(&entry->group->mark_mutex);
> >         spin_lock(&entry->lock);
> >         if (chunk->dead || !entry->inode) {
> >                 spin_unlock(&entry->lock);
> > @@ -258,7 +259,8 @@ static void untag_chunk(struct node *p)
> >         if (!new)
> >                 goto Fallback;
> >
> > -       if (fsnotify_add_mark(&new->mark, entry->group, entry->inode, NULL, 1)) {
> > +       if (fsnotify_add_mark_locked(&new->mark, entry->group, entry->inode,
> > +                                    NULL, 1)) {
> >                 fsnotify_put_mark(&new->mark);
> >                 goto Fallback;
> >         }
> > @@ -309,6 +311,7 @@ static void untag_chunk(struct node *p)
> >         spin_unlock(&hash_lock);
> >         spin_unlock(&entry->lock);
> >  out:
> > +       mutex_unlock(&entry->group->mark_mutex);
> >         fsnotify_put_mark(entry);
> >         spin_lock(&hash_lock);
> >  }
> > @@ -385,17 +388,21 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> >
> >         chunk_entry = &chunk->mark;
> >
> > +       mutex_lock(&old_entry->group->mark_mutex);
> >         spin_lock(&old_entry->lock);
> >         if (!old_entry->inode) {
> >                 /* old_entry is being shot, lets just lie */
> >                 spin_unlock(&old_entry->lock);
> > +               mutex_unlock(&old_entry->group->mark_mutex);
> >                 fsnotify_put_mark(old_entry);
> >                 free_chunk(chunk);
> >                 return -ENOENT;
> >         }
> >
> > -       if (fsnotify_add_mark(chunk_entry, old_entry->group, old_entry->inode, NULL, 1)) {
> > +       if (fsnotify_add_mark_locked(chunk_entry, old_entry->group,
> > +                                    old_entry->inode, NULL, 1)) {
> >                 spin_unlock(&old_entry->lock);
> > +               mutex_unlock(&old_entry->group->mark_mutex);
> >                 fsnotify_put_mark(chunk_entry);
> >                 fsnotify_put_mark(old_entry);
> >                 return -ENOSPC;
> > @@ -411,6 +418,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> >                 chunk->dead = 1;
> >                 spin_unlock(&chunk_entry->lock);
> >                 spin_unlock(&old_entry->lock);
> > +               mutex_unlock(&old_entry->group->mark_mutex);
> >
> >                 fsnotify_destroy_mark(chunk_entry, audit_tree_group);
> >
> > @@ -443,6 +451,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> >         spin_unlock(&hash_lock);
> >         spin_unlock(&chunk_entry->lock);
> >         spin_unlock(&old_entry->lock);
> > +       mutex_unlock(&old_entry->group->mark_mutex);
> >         fsnotify_destroy_mark(old_entry, audit_tree_group);
> >         fsnotify_put_mark(chunk_entry); /* drop initial reference */
> >         fsnotify_put_mark(old_entry); /* pair to fsnotify_find mark_entry */
> > --
> > 2.10.2
> >
> 
> 
> 
> -- 
> paul moore
> www.paul-moore.com
-- 
Jan Kara <jack at suse.com>
SUSE Labs, CR