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

Casey Schaufler
2022-03-16T00:07:12Z

On 3/15/2022 4:47 PM, Paul Moore wrote:
> 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);

Sure, I'll give this a try. Thanks for the review and suggestions.

>
>> 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;
>>
> --
> paul-moore.com