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Re: [Linux-ima-devel] [RFC PATCH 2/5] ima: Add ns_status for storing namespaced iint data
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From: Serge E. H. <se...@ha...> - 2017-07-25 20:49:41
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On Tue, Jul 25, 2017 at 04:15:25PM -0400, Mimi Zohar wrote:
> On Tue, 2017-07-25 at 14:43 -0500, Serge E. Hallyn wrote:
> > ...
> > > +static void free_ns_status_cache(struct ima_namespace *ns)
> > > +{
> > > + struct ns_status *status, *next;
> > > +
> > > + write_lock(&ns->ns_status_lock);
> > > + rbtree_postorder_for_each_entry_safe(status, next,
> > > + &ns->ns_status_tree, rb_node)
> > > + kmem_cache_free(ns->ns_status_cache, status);
> > > + ns->ns_status_tree = RB_ROOT;
> > > + write_unlock(&ns->ns_status_lock);
> > > + kmem_cache_destroy(ns->ns_status_cache);
> > > +}
> > > +
> > > static void destroy_ima_ns(struct ima_namespace *ns)
> > > {
> > > put_user_ns(ns->user_ns);
> > > ns_free_inum(&ns->ns);
> > > + free_ns_status_cache(ns);
> > > kfree(ns);
> > > }
> > >
> > > @@ -181,3 +198,106 @@ struct ima_namespace init_ima_ns = {
> > > .parent = NULL,
> > > };
> > > EXPORT_SYMBOL(init_ima_ns);
> > > +
> > > +/*
> > > + * __ima_ns_status_find - return the ns_status associated with an inode
> > > + */
> > > +static struct ns_status *__ima_ns_status_find(struct ima_namespace *ns,
> > > + struct inode *inode)
> > > +{
> > > + struct ns_status *status;
> > > + struct rb_node *n = ns->ns_status_tree.rb_node;
> > > +
> > > + while (n) {
> > > + status = rb_entry(n, struct ns_status, rb_node);
> > > +
> > > + if (inode < status->inode)
> > > + n = n->rb_left;
> > > + else if (inode->i_ino > status->i_ino)
> > > + n = n->rb_right;
> > > + else
> > > + break;
> > > + }
> > > + if (!n)
> > > + return NULL;
> > > +
> > > + return status;
> > > +}
> > > +
> > > +/*
> > > + * ima_ns_status_find - return the ns_status associated with an inode
> > > + */
> > > +static struct ns_status *ima_ns_status_find(struct ima_namespace *ns,
> > > + struct inode *inode)
> > > +{
> > > + struct ns_status *status;
> > > +
> > > + read_lock(&ns->ns_status_lock);
> > > + status = __ima_ns_status_find(ns, inode);
> > > + read_unlock(&ns->ns_status_lock);
> > > +
> > > + return status;
> > > +}
> > ...
> > > +
> > > +struct ns_status *ima_get_ns_status(struct ima_namespace *ns,
> > > + struct inode *inode)
> > > +{
> > > + struct ns_status *status;
> > > + int skip_insert = 0;
> > > +
> > > + status = ima_ns_status_find(ns, inode);
> > > + if (status) {
> > > + /*
> > > + * Unlike integrity_iint_cache we are not free'ing the
> > > + * ns_status data when the inode is free'd. So, in addition to
> > > + * checking the inode pointer, we need to make sure the
> > > + * (i_generation, i_ino) pair matches as well. In the future
> > > + * we might want to add support for lazily walking the rbtree
> > > + * to clean it up.
> > > + */
> > > + if (inode->i_ino == status->i_ino &&
> > > + inode->i_generation == status->i_generation)
> > > + return status;
> > > +
> > > + /* Same inode number is reused, overwrite the ns_status */
> > > + skip_insert = 1;
> > > + } else {
> > > + status = kmem_cache_alloc(ns->ns_status_cache, GFP_NOFS);
> > > + if (!status)
> > > + return ERR_PTR(-ENOMEM);
> > > + }
> >
> > What prevents the status from being freed between the read_lock
> > in ima_ns_status_find() and the write_lock in the following line?
> >
> > IIUC it's that ns is always current's ima_ns, which will pin the ns
> > and cause no statuses to be freed. But then the ns should probably
> > not be passed in here? Or a comment should say that ns must be
> > pinned?
> >
> > Just trying to make sure I understand the locking.
>
> iint's are only freed after the last reference to the inode is deleted
> in __fput(). Refer to ima_file_free(). ns_status is a bit different
> in that they are freed on namespace cleanup.
Ok, thanks - that sounds ok then.
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