linux-kernel - [PATCH] audit: remove the audit freelist

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Message-Id: <1479215774-29810-1-git-send-email-fw@strlen.de>
Date:   Tue, 15 Nov 2016 14:16:14 +0100
From:   Florian Westphal <fw@...len.de>
To:     linux-kernel@...r.kernel.org
Cc:     linux-audit@...hat.com, paul@...l-moore.com, eparis@...hat.com,
        Florian Westphal <fw@...len.de>
Subject: [PATCH] audit: remove the audit freelist

allows better debugging as freeing audit buffers now always honors slub
debug hooks (e.g. object poisoning) and leak checker can detect the
free operation.

Removal also results in a small speedup (using
single rule 'iptables -A INPUT -i lo -j AUDIT --type drop'):

super_netperf 4 -H 127.0.0.1 -l 360 -t UDP_RR -- -R 1 -m 64
Before:
294953
After:
298013

(alloc/free no longer serializes on spinlock, allocator can use percpu
 pool).

Signed-off-by: Florian Westphal <fw@...len.de>
---
 kernel/audit.c | 53 ++++++++---------------------------------------------
 1 file changed, 8 insertions(+), 45 deletions(-)

diff --git a/kernel/audit.c b/kernel/audit.c
index f1ca11613379..396868dc523a 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -131,13 +131,6 @@ static int audit_net_id;
 /* 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 sk_buff_head audit_skb_queue;
 /* queue of skbs to send to auditd when/if it comes back */
 static struct sk_buff_head audit_skb_hold_queue;
@@ -164,17 +157,11 @@ 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
+/* The audit_buffer is used when formatting an audit record.
+ * The caller 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;
@@ -1247,43 +1234,22 @@ __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);
+	kfree(ab);
 }
 
 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 audit_buffer *ab;
 	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;
-	}
+	ab = kmalloc(sizeof(*ab), gfp_mask);
+	if (!ab)
+		return NULL;
 
 	ab->ctx = ctx;
 	ab->gfp_mask = gfp_mask;
@@ -1294,13 +1260,10 @@ static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
 
 	nlh = nlmsg_put(ab->skb, 0, 0, type, 0, 0);
 	if (!nlh)
-		goto out_kfree_skb;
+		goto err;
 
 	return ab;
 
-out_kfree_skb:
-	kfree_skb(ab->skb);
-	ab->skb = NULL;
 err:
 	audit_buffer_free(ab);
 	return NULL;
-- 
2.7.3