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

[Paul Moore]

On Fri, Dec 23, 2016 at 8:24 AM, Jan Kara <jack at suse.cz> wrote:
> 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...

Okay, great.  I'll merge this patch in the audit/stable-4.10 branch
for Linus but there will likely be some delays due to
holidays/vacation on my end.

Thanks again for your help fixing this, I really appreciate it.

>> > 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