linux-kernel - [PATCH v33 25/29] Audit: Allow multiple records in an audit

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Message-Id: <20220310234632.16194-26-casey@schaufler-ca.com>
Date:   Thu, 10 Mar 2022 15:46:28 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     casey.schaufler@...el.com, jmorris@...ei.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org
Cc:     casey@...aufler-ca.com, linux-audit@...hat.com,
        keescook@...omium.org, john.johansen@...onical.com,
        penguin-kernel@...ove.sakura.ne.jp, paul@...l-moore.com,
        stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org
Subject: [PATCH v33 25/29] Audit: Allow multiple records in an audit_buffer

Replace the single skb pointer in an audit_buffer with
a list of skb pointers. Add the audit_stamp information
to the audit_buffer as there's no guarantee that there
will be an audit_context containing the stamp associated
with the event. At audit_log_end() time create auxiliary
records (none are currently defined) as have been added
to the list.

Suggested-by: Paul Moore <paul@...l-moore.com>
Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
---
 kernel/audit.c | 53 +++++++++++++++++++++++++++++++++-----------------
 1 file changed, 35 insertions(+), 18 deletions(-)

diff --git a/kernel/audit.c b/kernel/audit.c
index f012c3786264..4713e66a12af 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -197,8 +197,10 @@ static struct audit_ctl_mutex {
  * to place it on a transmit queue.  Multiple audit_buffers can be in
  * use simultaneously. */
 struct audit_buffer {
-	struct sk_buff       *skb;	/* formatted skb ready to send */
+	struct sk_buff       *skb;	/* the skb for audit_log functions */
+	struct sk_buff_head  skb_list;	/* formatted skbs, ready to send */
 	struct audit_context *ctx;	/* NULL or associated context */
+	struct audit_stamp   stamp;	/* audit stamp for these records */
 	gfp_t		     gfp_mask;
 };
 
@@ -1744,7 +1746,6 @@ static void audit_buffer_free(struct audit_buffer *ab)
 	if (!ab)
 		return;
 
-	kfree_skb(ab->skb);
 	kmem_cache_free(audit_buffer_cache, ab);
 }
 
@@ -1760,11 +1761,15 @@ static struct audit_buffer *audit_buffer_alloc(struct audit_context *ctx,
 	ab->skb = nlmsg_new(AUDIT_BUFSIZ, gfp_mask);
 	if (!ab->skb)
 		goto err;
-	if (!nlmsg_put(ab->skb, 0, 0, type, 0, 0))
+	if (!nlmsg_put(ab->skb, 0, 0, type, 0, 0)) {
+		kfree_skb(ab->skb);
 		goto err;
+	}
 
 	ab->ctx = ctx;
 	ab->gfp_mask = gfp_mask;
+	skb_queue_head_init(&ab->skb_list);
+	skb_queue_tail(&ab->skb_list, ab->skb);
 
 	return ab;
 
@@ -1825,7 +1830,6 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
 				     int type)
 {
 	struct audit_buffer *ab;
-	struct audit_stamp stamp;
 
 	if (audit_initialized != AUDIT_INITIALIZED)
 		return NULL;
@@ -1880,14 +1884,14 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, gfp_t gfp_mask,
 		return NULL;
 	}
 
-	audit_get_stamp(ab->ctx, &stamp);
+	audit_get_stamp(ab->ctx, &ab->stamp);
 	/* cancel dummy context to enable supporting records */
 	if (ctx)
 		ctx->dummy = 0;
 	audit_log_format(ab, "audit(%llu.%03lu:%u): ",
-			 (unsigned long long)stamp.ctime.tv_sec,
-			 stamp.ctime.tv_nsec/1000000,
-			 stamp.serial);
+			 (unsigned long long)ab->stamp.ctime.tv_sec,
+			 ab->stamp.ctime.tv_nsec/1000000,
+			 ab->stamp.serial);
 
 	return ab;
 }
@@ -2378,26 +2382,19 @@ int audit_signal_info(int sig, struct task_struct *t)
 }
 
 /**
- * audit_log_end - end one audit record
- * @ab: the audit_buffer
+ * __audit_log_end - end one audit record
+ * @skb: the buffer to send
  *
  * We can not do a netlink send inside an irq context because it blocks (last
  * arg, flags, is not set to MSG_DONTWAIT), so the audit buffer is placed on a
  * queue and a kthread is scheduled to remove them from the queue outside the
  * irq context.  May be called in any context.
  */
-void audit_log_end(struct audit_buffer *ab)
+static void __audit_log_end(struct sk_buff *skb)
 {
-	struct sk_buff *skb;
 	struct nlmsghdr *nlh;
 
-	if (!ab)
-		return;
-
 	if (audit_rate_check()) {
-		skb = ab->skb;
-		ab->skb = NULL;
-
 		/* setup the netlink header, see the comments in
 		 * kauditd_send_multicast_skb() for length quirks */
 		nlh = nlmsg_hdr(skb);
@@ -2408,6 +2405,26 @@ void audit_log_end(struct audit_buffer *ab)
 		wake_up_interruptible(&kauditd_wait);
 	} else
 		audit_log_lost("rate limit exceeded");
+}
+
+/**
+ * audit_log_end - end one audit record
+ * @ab: the audit_buffer
+ *
+ * We can not do a netlink send inside an irq context because it blocks (last
+ * arg, flags, is not set to MSG_DONTWAIT), so the audit buffer is placed on a
+ * queue and a kthread is scheduled to remove them from the queue outside the
+ * irq context.  May be called in any context.
+ */
+void audit_log_end(struct audit_buffer *ab)
+{
+	struct sk_buff *skb;
+
+	if (!ab)
+		return;
+
+	while ((skb = skb_dequeue(&ab->skb_list)))
+		__audit_log_end(skb);
 
 	audit_buffer_free(ab);
 }
-- 
2.31.1