[RFC PATCH 4/4] audit: use kmem_cache to manage the audit_buffer cache

[Paul Moore]

... and I forgot to explicitly add Florian to the email, fixing that now.

On Tue, Mar 21, 2017 at 2:59 PM, Paul Moore <pmoore at redhat.com> wrote:
> From: Paul Moore <paul at paul-moore.com>
>
> 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 at strlen.de>
> Signed-off-by: Paul Moore <paul at paul-moore.com>
> ---
>  kernel/audit.c |   66 ++++++++++++++------------------------------------------
>  1 file changed, 17 insertions(+), 49 deletions(-)
>
> diff --git a/kernel/audit.c b/kernel/audit.c
> index b718bf3a73f8..f78cdd75a4d2 100644
> --- 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;
> @@ -193,17 +189,12 @@ 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;
> @@ -1489,6 +1480,10 @@ 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);
>
> @@ -1557,60 +1552,33 @@ __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;
>
> --
> Linux-audit mailing list
> Linux-audit at redhat.com
> https://www.redhat.com/mailman/listinfo/linux-audit

-- 
paul moore
www.paul-moore.com