From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Paris Subject: Re: [RFC][PATCH] audit: Simplify by assuming the callers socket buffer is large enough Date: Mon, 10 Mar 2014 17:57:46 -0400 Message-ID: <1394488666.17193.16.camel@localhost> References: <7457128.6VP2v68V93@x2> <87wqg8zfj4.fsf@xmission.com> <1394232722.17779.57.camel@flatline.rdu.redhat.com> <20140310.153001.1202621819107314058.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: rgb@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-audit@redhat.com, ebiederm@xmission.com, akpm@linux-foundation.org To: David Miller Return-path: In-Reply-To: <20140310.153001.1202621819107314058.davem@davemloft.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-audit-bounces@redhat.com Errors-To: linux-audit-bounces@redhat.com List-Id: netdev.vger.kernel.org On Mon, 2014-03-10 at 15:30 -0400, David Miller wrote: > From: Eric Paris > Date: Fri, 07 Mar 2014 17:52:02 -0500 > > > The second user Eric patched, audit_send_list(), can grow without bound. > > The number of skb's is going to be the size of the number of audit rules > > that root loaded. We run the list of rules, generate an skb per rule, > > and add all of them to an skb_buff_head. We then pass the skb_buff_head > > to a kthread so that current will be able to read/drain the socket. > > There really is no limit to how big the skb_buff_head could possibly > > grow. This doesn't necessarily absolutely have to be lossless but it > > can actually quite reasonably be a whole lot of data that needs to get > > sent. I know of no way to deliver unbounded lengths of data to the > > current task via netlink without blocking on more space in the socket. > > Even if the socket rmem was MAX_INT, how can we deliver more? The rule > > size is unbounded. How do I get an unbounded amount of data onto this > > side of the socket when I have to generate it all during the request... > > This is what netlink dumps are for. It is how we are able to dump > routing tables with millions of routes to userspace. > > By using normal netlink requests and netlink_unicast() for this, you > are ignoring an entire mechanism in netlink designed specifically to > handle this kind of situation. > > Netlink dumps track state and build one or more SKBs (as necessary), > one by one, to form the reply. It implements flow control, state > tracking for iteration, optimized SKB sizing and allocation, etc. Awesome. I'll see what I can find!