[PATCH v33 25/29] Audit: Allow multiple records in an audit_buffer

Casey Schaufler
2022-03-10T23:59:46Z

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@paul-moore.com>
Signed-off-by: Casey Schaufler <casey@schaufler-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