On Thu 22-12-16 18:18:36, Paul Moore wrote:
> On Thu, Dec 22, 2016 at 4:15 AM, Jan Kara <jack@xxxxxxx> 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@xxxxxxxxxxxxxx>
> > Signed-off-by: Jan Kara <jack@xxxxxxx>
> > ---
> > 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@xxxxxxxx>
SUSE Labs, CR
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