From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 688FDC7EE30 for ; Thu, 2 Mar 2023 20:11:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229816AbjCBULT (ORCPT ); Thu, 2 Mar 2023 15:11:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43202 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229642AbjCBULR (ORCPT ); Thu, 2 Mar 2023 15:11:17 -0500 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [IPv6:2a03:a000:7:0:5054:ff:fe1c:15ff]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2F0972384E; Thu, 2 Mar 2023 12:11:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description; bh=ZAPTNfiVxd4koXwKff5tqp/NDLJPyM69bOUmGGBfyTo=; b=jmdx6u4/CBKUlztqdO6dW4gYLL zIE2jLHI3fWpuzzj9N/N9hkcLCwfOwHHADSlDXG8HfKGOw9Ndrde9bt7LnzcFy734s0TZh43vlZ7S lzBFCN/IzWnL5YPfgptx4bDZxPeSv1JAKSUWOtvAl7Do5BV+HVMDRM2b+gjfdD5oLOgH3btWV6w28 w/DNUmXS5pk3Bnvb8P5V21ADparX7n4AY4UJu+aDajakD2UOOW0jLNzTwB2LadW6CXndLtAkHiIYg /LUmyPNmJS3bTUyboYX0UAo9CVp5tAKw108hldMbtRC+Sx96KU6D9rQRfs9mik+Kqv2Cb2qPZiocg U4x+6R3g==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1pXpGf-00DOIr-00; Thu, 02 Mar 2023 20:11:09 +0000 Date: Thu, 2 Mar 2023 20:11:08 +0000 From: Al Viro To: Kees Cook Cc: Linus Torvalds , Mateusz Guzik , Eric Biggers , Alexander Potapenko , Christian Brauner , serge@hallyn.com, paul@paul-moore.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Subject: Re: [PATCH v3 2/2] vfs: avoid duplicating creds in faccessat if possible Message-ID: References: <20230302083025.khqdizrnjkzs2lt6@wittgenstein> <6400fedb.170a0220.ece29.04b8@mx.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6400fedb.170a0220.ece29.04b8@mx.google.com> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 02, 2023 at 11:54:03AM -0800, Kees Cook wrote: > On Thu, Mar 02, 2023 at 07:19:49PM +0000, Al Viro wrote: > > On Thu, Mar 02, 2023 at 11:10:03AM -0800, Linus Torvalds wrote: > > > On Thu, Mar 2, 2023 at 11:03 AM Linus Torvalds > > > wrote: > > > > > > > > It might be best if we actually exposed it as a SLAB_SKIP_ZERO thing, > > > > just to make it possible to say - exactly in situations like this - > > > > that this particular slab cache has no advantage from pre-zeroing. > > > > > > Actually, maybe it's just as well to keep it per-allocation, and just > > > special-case getname_flags() itself. > > > > > > We could replace the __getname() there with just a > > > > > > kmem_cache_alloc(names_cachep, GFP_KERNEL | __GFP_SKIP_ZERO); > > > > > > we're going to overwrite the beginning of the buffer with the path we > > > copy from user space, and then we'd have to make people comfortable > > > with the fact that even with zero initialization hardening on, the > > > space after the filename wouldn't be initialized... > > > > ACK; same in getname_kernel() and sys_getcwd(), at the very least. > > FWIW, much earlier analysis suggested opting out these kmem caches: > > buffer_head > names_cache > mm_struct > anon_vma > skbuff_head_cache > skbuff_fclone_cache I would probably add dentry_cache to it; the only subtle part is ->d_iname and I'm convinced that explicit "make sure there's a NUL at the very end" is enough.