[PATCH 10/10] audit: Replace chunk attached to mark instead of replacing mark

[Paul Moore]

On Tue, Jul 10, 2018 at 6:02 AM Jan Kara <jack at suse.cz> wrote:
> Audit tree code currently associates new fsnotify mark with each new
> chunk. As chunk attached to an inode is replaced when new tag is added /
> removed, we also need to remove old fsnotify mark and add a new one on
> such occasion.  This is cumbersome and makes locking rules somewhat
> difficult to follow.
>
> Fix these problems by allocating fsnotify mark independently of chunk
> and keeping it all the time while there is some chunk attached to an
> inode. Also add documentation about the locking rules so that things are
> easier to follow.
>
> Signed-off-by: Jan Kara <jack at suse.cz>
> ---
>  kernel/audit_tree.c | 163 +++++++++++++++++++++++++++-------------------------
>  1 file changed, 85 insertions(+), 78 deletions(-)

This is a really nice improvement, thanks!

> diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> index aec9b27a20ff..40f61de77dd0 100644
> --- a/kernel/audit_tree.c
> +++ b/kernel/audit_tree.c
> @@ -272,6 +273,20 @@ static struct audit_chunk *find_chunk(struct node *p)
>         return container_of(p, struct audit_chunk, owners[0]);
>  }
>
> +static void replace_mark_chunk(struct fsnotify_mark *entry,
> +                              struct audit_chunk *chunk)
> +{
> +       struct audit_chunk *old;
> +
> +       assert_spin_locked(&hash_lock);
> +       old = AUDIT_M(entry)->chunk;
> +       AUDIT_M(entry)->chunk = chunk;
> +       if (chunk)
> +               chunk->mark = entry;
> +       if (old)
> +               old->mark = NULL;

Is it necessary that we check to see if chunk and old are non-NULL?
It seems like we would always want to set chunk->mark to entry and set
old->mark to NULL, yes?

> @@ -321,29 +341,31 @@ static void untag_chunk(struct node *p)
>
>         mutex_lock(&entry->group->mark_mutex);
>         /*
> -        * mark_mutex protects mark from getting detached and thus also from
> -        * mark->connector->obj getting NULL.
> +        * mark_mutex protects mark stabilizes chunk attached to the mark so we
> +        * can check whether it didn't change while we've dropped hash_lock.

I think your new text could use some revision, the "protects mark
stabilizes chunk" is odd.

>          */
> -       if (chunk->dead || !(entry->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
> +       if (!(entry->flags & FSNOTIFY_MARK_FLAG_ATTACHED) ||
> +           AUDIT_M(entry)->chunk != chunk) {
>                 mutex_unlock(&entry->group->mark_mutex);
>                 if (new)
> -                       fsnotify_put_mark(new->mark);
> +                       kfree(new);

Since we are just calling kfree() now we can do away with the "if (new)" check.

--
paul moore
www.paul-moore.com