Messages in this thread | | | Subject | Re: [RFC PATCH 2/5] ima: Add ns_status for storing namespaced iint data | From | Stefan Berger <> | Date | Tue, 25 Jul 2017 16:25:08 -0400 |
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On 07/25/2017 04:15 PM, 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.
It should be possible to move the write_lock() above the
status = ima_ns_status_find(ns, inode);
and instead call __ima_ns_status_find() with the write_lock() held.
Stefan
> > Mimi > >>> + write_lock(&ns->ns_status_lock); >>> + >>> + if (!skip_insert) >>> + insert_ns_status(ns, inode, status); >>> + >>> + status->inode = inode; >>> + status->i_ino = inode->i_ino; >>> + status->i_generation = inode->i_generation; >>> + status->flags = 0UL; >>> + write_unlock(&ns->ns_status_lock); >>> + >>> + return status; >>> +} >>> -- >>> 2.9.
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