>>>>> "Eric" == Eric Paris <eparis@xxxxxxxxxx> writes: Eric> The IMA code needs to store the number of tasks which have an Eric> open fd granting permission to write a file even when IMA is not Eric> in use. It needs this information in order to be enabled at a Eric> later point in time without losing it's integrity garantees. This sounds completely wrong to me. If I disable IMA (but have the sucker compiled in due to a vendor...) I don't want *any* overhead, and this is speaking using my SysAdmin hat for people who do EDA design work, and having fast systems is key for us. IMA is NOT. We disable SELINUX too, because of the overhead and the maintenance nightmare. If IMA isn't enabled right from the get-go, how can you ensure integrity? And how can you ensure integrity if root is compromised? If root can disable IMA, screw around with a file, then turn on IMA again without the change being guarrentteed to be noticed (and not because the attacked didn't do the attack perfectly!) what's the use? How does this help any? To quote from: http://domino.research.ibm.com/comm/research_people.nsf/pages/sailer.ima.html What IMA is not IMA is not controlling your system. IMA is non-intrusive and is best described as an independent observer collecting integrity information of loaded code or sensitive application files on demand. Consequently, IMA does not prevent a system from illegal behavior that might compromise the system including the integrity measurement architecture itself. Recognizing the danger of being by-passed, IMA simply invalidates its own measurement list by invalidating the TPM integrity aggregate and thereby rendering the evidence useless (non-verifiable) until it is reset during the next system reboot. For example, if applications write directly to a device (/dev/hda, /dev/sda) or kernel memory (/dev/kmem), then IMA invalidates the TPM aggregate. IMA is not a Digital Rights Management tool either. IMA collects evidence on the local system, which can be used for many purposes but whose release is fully controlled by the local system. It is getting harder to lie about what you are running when you use IMA; no doubt about it. However, if system security is going to be reality, systems that lie at will seem not a convincing alternative in a distributed environment where the weakest link determines the security of the distributed service. The price to pay is that properties must be established securely and that the balance between use and abuse of knowledge about such properties as well as the validity of requiring such evidence (e.g., before connecting a system to a video-on-demand service) must be controlled by rules that are enforced the same way they are in other areas of our daily life (most likely by laws). So basically, IMA is super duper tripwire with the ability to allow some remote system to come in and ask for your Hashes. And if you screw around with it, it immediately disables itself. Which seems to fly in the face of your claim that it needs to be able to re-enable itself by tracking open inodes even when disabled. Eric> At the moment that means we store a little bit of data about Eric> every inode in a cache. We use a radix tree key'd on the Eric> inode's memory address. Dave Chinner pointed out that a radix Eric> tree is a terrible data structure for such a sparse key space. Eric> This patch switches to using an rbtree which should be more Eric> efficient. As the number of inodes goes up (say during a backup which reads them...) won't the size of this cache go up as well, even when IMA is disabled? Why is this overhead even needed? This should all just be ripped out. John Eric> Bug report from Dave: Eric> I just noticed that slabtop Eric> was reportingi an awfully high usage of radix tree nodes: Eric> OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME Eric> 4200331 2778082 66% 0.55K 144839 29 2317424K radix_tree_node Eric> 2321500 2060290 88% 1.00K 72581 32 2322592K xfs_inode Eric> 2235648 2069791 92% 0.12K 69864 32 279456K iint_cache Eric> That is, 2.7M radix tree nodes are allocated, and the cache itself Eric> is consuming 2.3GB of RAM. I know that the XFS inodei caches are Eric> indexed by radix tree node, but for 2 million cached inodes that Eric> would mean a density of 1 inode per radix tree node, which for a Eric> system with 16M inodes in the filsystems is an impossibly low Eric> density. The worst I've seen in a production system like kernel.org Eric> is about 20-25% density, which would mean about 150â200k radix tree Eric> nodes for that many inodes. So it's not the inode cache. Eric> So I looked up what the iint_cache was. It appears to used for storing Eric> per-inode IMA information, and uses a radix tree for indexing. Eric> It uses the *address* of the struct inode as the indexing key. That Eric> means the key space is extremely sparse - for XFS the struct inode Eric> addresses are approximately 1000 bytes apart, which means the Eric> closest the radix tree index keys get is ~1000. Which means Eric> that there is a single entry per radix tree leaf node, so the radix Eric> tree is using roughly 550 bytes for every 120byte structure being Eric> cached. For the above example, it's probably wasting close to 1GB of Eric> RAM.... Eric> Reported-by: Dave Chinner <david@xxxxxxxxxxxxx> Eric> Signed-off-by: Eric Paris <eparis@xxxxxxxxxx> Eric> Acked-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> Eric> --- Eric> security/integrity/ima/ima.h | 6 +- Eric> security/integrity/ima/ima_iint.c | 105 +++++++++++++++++++++++++------------ Eric> 2 files changed, 75 insertions(+), 36 deletions(-) Eric> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h Eric> index 3fbcd1d..7557791 100644 Eric> --- a/security/integrity/ima/ima.h Eric> +++ b/security/integrity/ima/ima.h Eric> @@ -100,6 +100,8 @@ static inline unsigned long ima_hash_key(u8 *digest) Eric> /* integrity data associated with an inode */ Eric> struct ima_iint_cache { Eric> + struct rb_node rb_node; /* rooted in ima_iint_tree */ Eric> + struct inode *inode; /* back pointer to inode in question */ Eric> u64 version; /* track inode changes */ Eric> unsigned long flags; Eric> u8 digest[IMA_DIGEST_SIZE]; Eric> @@ -108,7 +110,6 @@ struct ima_iint_cache { Eric> long writecount; /* measured files writecount */ Eric> long opencount; /* opens reference count */ Eric> struct kref refcount; /* ima_iint_cache reference count */ Eric> - struct rcu_head rcu; Eric> }; Eric> /* LIM API function definitions */ Eric> @@ -122,13 +123,12 @@ int ima_store_template(struct ima_template_entry *entry, int violation, Eric> void ima_template_show(struct seq_file *m, void *e, Eric> enum ima_show_type show); Eric> -/* radix tree calls to lookup, insert, delete Eric> +/* rbtree tree calls to lookup, insert, delete Eric> * integrity data associated with an inode. Eric> */ Eric> struct ima_iint_cache *ima_iint_insert(struct inode *inode); Eric> struct ima_iint_cache *ima_iint_find_get(struct inode *inode); Eric> void iint_free(struct kref *kref); Eric> -void iint_rcu_free(struct rcu_head *rcu); Eric> /* IMA policy related functions */ Eric> enum ima_hooks { FILE_CHECK = 1, FILE_MMAP, BPRM_CHECK }; Eric> diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c Eric> index afba4ae..8395f0f 100644 Eric> --- a/security/integrity/ima/ima_iint.c Eric> +++ b/security/integrity/ima/ima_iint.c Eric> @@ -12,21 +12,48 @@ Eric> * File: ima_iint.c Eric> * - implements the IMA hooks: ima_inode_alloc, ima_inode_free Eric> * - cache integrity information associated with an inode Eric> - * using a radix tree. Eric> + * using a rbtree tree. Eric> */ Eric> #include <linux/slab.h> Eric> #include <linux/module.h> Eric> #include <linux/spinlock.h> Eric> -#include <linux/radix-tree.h> Eric> +#include <linux/rbtree.h> Eric> #include "ima.h" Eric> -RADIX_TREE(ima_iint_store, GFP_ATOMIC); Eric> -DEFINE_SPINLOCK(ima_iint_lock); Eric> +static struct rb_root ima_iint_tree = RB_ROOT; Eric> +static DEFINE_SPINLOCK(ima_iint_lock); Eric> static struct kmem_cache *iint_cache __read_mostly; Eric> int iint_initialized = 0; Eric> -/* ima_iint_find_get - return the iint associated with an inode Eric> +/* Eric> + * __ima_iint_find - return the iint associated with an inode Eric> + */ Eric> +static struct ima_iint_cache *__ima_iint_find(struct inode *inode) Eric> +{ Eric> + struct ima_iint_cache *iint; Eric> + struct rb_node *n = ima_iint_tree.rb_node; Eric> + Eric> + assert_spin_locked(&ima_iint_lock); Eric> + Eric> + while (n) { Eric> + iint = rb_entry(n, struct ima_iint_cache, rb_node); Eric> + Eric> + if (inode < iint->inode) Eric> + n = n->rb_left; Eric> + else if (inode > iint->inode) Eric> + n = n->rb_right; Eric> + else Eric> + break; Eric> + } Eric> + if (!n) Eric> + return NULL; Eric> + Eric> + return iint; Eric> +} Eric> + Eric> +/* Eric> + * ima_iint_find_get - return the iint associated with an inode Eric> * Eric> * ima_iint_find_get gets a reference to the iint. Caller must Eric> * remember to put the iint reference. Eric> @@ -35,13 +62,12 @@ struct ima_iint_cache *ima_iint_find_get(struct inode *inode) Eric> { Eric> struct ima_iint_cache *iint; Eric> - rcu_read_lock(); Eric> - iint = radix_tree_lookup(&ima_iint_store, (unsigned long)inode); Eric> - if (!iint) Eric> - goto out; Eric> - kref_get(&iint->refcount); Eric> -out: Eric> - rcu_read_unlock(); Eric> + spin_lock(&ima_iint_lock); Eric> + iint = __ima_iint_find(inode); Eric> + if (iint) Eric> + kref_get(&iint->refcount); Eric> + spin_unlock(&ima_iint_lock); Eric> + Eric> return iint; Eric> } Eric> @@ -51,25 +77,43 @@ out: Eric> */ Eric> int ima_inode_alloc(struct inode *inode) Eric> { Eric> - struct ima_iint_cache *iint = NULL; Eric> - int rc = 0; Eric> + struct rb_node **p; Eric> + struct rb_node *new_node, *parent = NULL; Eric> + struct ima_iint_cache *new_iint, *test_iint; Eric> + int rc; Eric> - iint = kmem_cache_alloc(iint_cache, GFP_NOFS); Eric> - if (!iint) Eric> + new_iint = kmem_cache_alloc(iint_cache, GFP_NOFS); Eric> + if (!new_iint) Eric> return -ENOMEM; Eric> - rc = radix_tree_preload(GFP_NOFS); Eric> - if (rc < 0) Eric> - goto out; Eric> + new_iint->inode = inode; Eric> + new_node = &new_iint->rb_node; Eric> spin_lock(&ima_iint_lock); Eric> - rc = radix_tree_insert(&ima_iint_store, (unsigned long)inode, iint); Eric> + Eric> + p = &ima_iint_tree.rb_node; Eric> + while (*p) { Eric> + parent = *p; Eric> + test_iint = rb_entry(parent, struct ima_iint_cache, rb_node); Eric> + Eric> + rc = -EEXIST; Eric> + if (inode < test_iint->inode) Eric> + p = &(*p)->rb_left; Eric> + else if (inode > test_iint->inode) Eric> + p = &(*p)->rb_right; Eric> + else Eric> + goto out_err; Eric> + } Eric> + Eric> + rb_link_node(new_node, parent, p); Eric> + rb_insert_color(new_node, &ima_iint_tree); Eric> + Eric> spin_unlock(&ima_iint_lock); Eric> - radix_tree_preload_end(); Eric> -out: Eric> - if (rc < 0) Eric> - kmem_cache_free(iint_cache, iint); Eric> + return 0; Eric> +out_err: Eric> + spin_unlock(&ima_iint_lock); Eric> + kref_put(&new_iint->refcount, iint_free); Eric> return rc; Eric> } Eric> @@ -99,13 +143,6 @@ void iint_free(struct kref *kref) Eric> kmem_cache_free(iint_cache, iint); Eric> } Eric> -void iint_rcu_free(struct rcu_head *rcu_head) Eric> -{ Eric> - struct ima_iint_cache *iint = container_of(rcu_head, Eric> - struct ima_iint_cache, rcu); Eric> - kref_put(&iint->refcount, iint_free); Eric> -} Eric> - Eric> /** Eric> * ima_inode_free - called on security_inode_free Eric> * @inode: pointer to the inode Eric> @@ -117,10 +154,12 @@ void ima_inode_free(struct inode *inode) Eric> struct ima_iint_cache *iint; Eric> spin_lock(&ima_iint_lock); Eric> - iint = radix_tree_delete(&ima_iint_store, (unsigned long)inode); Eric> + iint = __ima_iint_find(inode); Eric> + if (iint) Eric> + rb_erase(&iint->rb_node, &ima_iint_tree); Eric> spin_unlock(&ima_iint_lock); Eric> if (iint) Eric> - call_rcu(&iint->rcu, iint_rcu_free); Eric> + kref_put(&iint->refcount, iint_free); Eric> } Eric> static void init_once(void *foo) Eric> -- Eric> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Eric> the body of a message to majordomo@xxxxxxxxxxxxxxx Eric> More majordomo info at http://vger.kernel.org/majordomo-info.html Eric> Please read the FAQ at http://www.tux.org/lkml/ -- -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
