From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. Bruce Fields" Subject: Re: [PATCH 13/15] SUNRPC: RPC buffer size estimates are too large Date: Wed, 24 Jan 2007 15:47:24 -0500 Message-ID: <20070124204724.GB6587@fieldses.org> References: <20070124191704.31133.12713.stgit@localhost.localdomain> <20070124192020.31133.78494.stgit@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: nfs@lists.sourceforge.net, trond.myklebust@fys.uio.no To: Chuck Lever Return-path: Received: from sc8-sf-mx2-b.sourceforge.net ([10.3.1.92] helo=mail.sourceforge.net) by sc8-sf-list2-new.sourceforge.net with esmtp (Exim 4.43) id 1H9p1k-0001eX-AI for nfs@lists.sourceforge.net; Wed, 24 Jan 2007 12:47:31 -0800 Received: from mail.fieldses.org ([66.93.2.214] helo=fieldses.org) by mail.sourceforge.net with esmtps (TLSv1:AES256-SHA:256) (Exim 4.44) id 1H9p1k-0004mX-SN for nfs@lists.sourceforge.net; Wed, 24 Jan 2007 12:47:30 -0800 In-Reply-To: <20070124192020.31133.78494.stgit@localhost.localdomain> List-Id: "Discussion of NFS under Linux development, interoperability, and testing." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: nfs-bounces@lists.sourceforge.net Errors-To: nfs-bounces@lists.sourceforge.net On Wed, Jan 24, 2007 at 02:20:20PM -0500, Chuck Lever wrote: > The RPC buffer size estimation logic in net/sunrpc/clnt.c always > significantly overestimates the requirements for the buffer size. > A little instrumentation demonstrated that in fact rpc_malloc was never > allocating the buffer from the mempool, but almost always called kmalloc. > > To compute the size of the RPC buffer more precisely, split p_bufsiz into > two fields; one for the argument size, and one for the result size. > > So now we will compute the sum of the exact call and reply header sizes, > and split the RPC buffer precisely between the two. That should keep > almost all RPC buffers within the 2KiB buffer mempool limit. One other worry: after this patch, as I understand it, a small mistake in any of the definitions of the *_sz macros could allow a buffer overflow that RPC_SLACK_SPACE previously prevented. Those definitions are all handwritten, and I'd be suprised if there aren't at least a few minor errors. I'd certainly rather have these calculations be exact than depend on this big RPC_SLACK_SPACE fudge factor, but is there some way we could verify those macros first? --b. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ NFS maillist - NFS@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/nfs