audit: use kmem_cache to manage the audit_buffer cache

The audit subsystem implemented its own buffer cache mechanism which
is a bit silly these days when we could use the kmem_cache construct.

Some credit is due to Florian Westphal for originally proposing that
we remove the audit cache implementation in favor of simple
kmalloc()/kfree() calls, but I would rather have a dedicated slab
cache to ease debugging and future stats/performance work.

Cc: Florian Westphal <fw@strlen.de>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/kernel/audit.c b/kernel/audit.c
index 41efd2ad1931cfd5a3009fda4355ab0d1dd2a29c..10bc2bad2adf0107385a974b2fce437fd91c89c7 100644 (file)
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -59,6 +59,7 @@
 #include <linux/mutex.h>
 #include <linux/gfp.h>
 #include <linux/pid.h>
+#include <linux/slab.h>
 
 #include <linux/audit.h>
 
@@ -152,12 +153,7 @@ static atomic_t    audit_lost = ATOMIC_INIT(0);
 /* Hash for inode-based rules */
 struct list_head audit_inode_hash[AUDIT_INODE_BUCKETS];
 
-/* The audit_freelist is a list of pre-allocated audit buffers (if more
- * than AUDIT_MAXFREE are in use, the audit buffer is freed instead of
- * being placed on the freelist). */
-static DEFINE_SPINLOCK(audit_freelist_lock);
-static int        audit_freelist_count;
-static LIST_HEAD(audit_freelist);
+static struct kmem_cache *audit_buffer_cache;
 
 /* queue msgs to send via kauditd_task */
 static struct sk_buff_head audit_queue;
@@ -192,17 +188,12 @@ DEFINE_MUTEX(audit_cmd_mutex);
  * should be at least that large. */
 #define AUDIT_BUFSIZ 1024
 
-/* AUDIT_MAXFREE is the number of empty audit_buffers we keep on the
- * audit_freelist.  Doing so eliminates many kmalloc/kfree calls. */
-#define AUDIT_MAXFREE  (2*NR_CPUS)
-
 /* The audit_buffer is used when formatting an audit record.  The caller
  * locks briefly to get the record off the freelist or to allocate the
  * buffer, and locks briefly to send the buffer to the netlink layer or
  * to place it on a transmit queue.  Multiple audit_buffers can be in
  * use simultaneously. */
 struct audit_buffer {
-       struct list_head     list;
        struct sk_buff       *skb;      /* formatted skb ready to send */
        struct audit_context *ctx;      /* NULL or associated context */
        gfp_t                gfp_mask;
@@ -1486,6 +1477,10 @@ static int __init audit_init(void)
        if (audit_initialized == AUDIT_DISABLED)
                return 0;
 
+       audit_buffer_cache = kmem_cache_create("audit_buffer",
+                                              sizeof(struct audit_buffer),
+                                              0, SLAB_PANIC, NULL);
+
        memset(&auditd_conn, 0, sizeof(auditd_conn));
        spin_lock_init(&auditd_conn.lock);
 
@@ -1554,60 +1549,33 @@ __setup("audit_backlog_limit=", audit_backlog_limit_set);
 
 static void audit_buffer_free(struct audit_buffer *ab)
 {
-       unsigned long flags;
-
        if (!ab)
                return;
 
        kfree_skb(ab->skb);
-       spin_lock_irqsave(&audit_freelist_lock, flags);
-       if (audit_freelist_count > AUDIT_MAXFREE)
-               kfree(ab);
-       else {
-               audit_freelist_count++;
-               list_add(&ab->list, &audit_freelist);
-       }
-       spin_unlock_irqrestore(&audit_freelist_lock, flags);
+       kmem_cache_free(audit_buffer_cache, ab);
 }
 
-static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
-                                               gfp_t gfp_mask, int type)
+static struct audit_buffer *audit_buffer_alloc(struct audit_context *ctx,
+                                              gfp_t gfp_mask, int type)
 {
-       unsigned long flags;
-       struct audit_buffer *ab = NULL;
-       struct nlmsghdr *nlh;
-
-       spin_lock_irqsave(&audit_freelist_lock, flags);
-       if (!list_empty(&audit_freelist)) {
-               ab = list_entry(audit_freelist.next,
-                               struct audit_buffer, list);
-               list_del(&ab->list);
-               --audit_freelist_count;
-       }
-       spin_unlock_irqrestore(&audit_freelist_lock, flags);
-
-       if (!ab) {
-               ab = kmalloc(sizeof(*ab), gfp_mask);
-               if (!ab)
-                       goto err;
-       }
+       struct audit_buffer *ab;
 
-       ab->ctx = ctx;
-       ab->gfp_mask = gfp_mask;
+       ab = kmem_cache_alloc(audit_buffer_cache, gfp_mask);
+       if (!ab)
+               return NULL;
 
        ab->skb = nlmsg_new(AUDIT_BUFSIZ, gfp_mask);
        if (!ab->skb)
                goto err;
+       if (!nlmsg_put(ab->skb, 0, 0, type, 0, 0))
+               goto err;
 
-       nlh = nlmsg_put(ab->skb, 0, 0, type, 0, 0);
-       if (!nlh)
-               goto out_kfree_skb;
+       ab->ctx = ctx;
+       ab->gfp_mask = gfp_mask;
 
        return ab;
 
-out_kfree_skb:
-       kfree_skb(ab->skb);
-       ab->skb = NULL;
 err:
        audit_buffer_free(ab);
        return NULL;