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

Paul Moore
2022-03-15T23:47:56Z

On Thu, Mar 10, 2022 at 6:59 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>
> 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);

I like the safety in knowing that audit_buffer_free() would free the
ab->skb memory, I'm not sure I want to get rid of that. With the
understanding that ab->skb is always going to be present somewhere in
ab->skb_list, any reason not to do something like this?

while ((skb = skb_dequeue(&ab->skb_list)))
kfree_skb(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;
> + }

Assuming we restore the audit_buffer_free() functionality as mentioned
above, if we move the ab->skb_list init and enqueue calls before we
attempt the nlmsg_put() we can drop the kfree_skb() call and just use
the existing audit_buffer_free() call at the err target.

> 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;
>

--
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