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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E005AC3A589 for ; Thu, 15 Aug 2019 15:30:53 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B228920644 for ; Thu, 15 Aug 2019 15:30:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="re6n/C+h" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B228920644 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=oWEwm3L7q4XR0A8OEGYAPnMEsEEawuG35mougtM3Z5A=; b=re6n/C+hOLb0fB vf3vgJj36LVCbd+RMlnOaF3slPP27Lw8ldEE3cfo6Xpm+YUmFew59m+8s/9l1UiSz7IYJ7XstKkUs UISwR+kxE2O5Udq3peLHy1z38KMsr5ht9iXdX8rEe1cOhWdNLmY6UTlfpQuA51gN6H1ZBGRHJkxsi UQkpf2W25PFc9DK6O769DJGfFt9CC+WFdkrpY4nJwKoLPVGudv07gUmEwv0sjaBZkaAks7HC8V1do 1URZfFvmWShikvfpnzPSij3OzwbRF72FSwoHGgYjUW4GyOsnJAulEAxu8OBPoMlq2FLNYDxPHHxj0 T/waDfxVC1caw+tmrWbA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hyHi1-0006lm-2L; Thu, 15 Aug 2019 15:30:37 +0000 Received: from mx2.suse.de ([195.135.220.15] helo=mx1.suse.de) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hyHhw-0006lD-Vm; Thu, 15 Aug 2019 15:30:36 +0000 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 84639B02E; Thu, 15 Aug 2019 15:30:28 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id F3E6E1E4200; Thu, 15 Aug 2019 17:30:24 +0200 (CEST) Date: Thu, 15 Aug 2019 17:30:24 +0200 From: Jan Kara To: Mark Salyzyn Subject: Re: [PATCH v2] Add flags option to get xattr method paired to __vfs_getxattr Message-ID: <20190815153024.GP14313@quack2.suse.cz> References: <20190813145527.26289-1-salyzyn@android.com> <20190814110022.GB26273@quack2.suse.cz> <71d66fd1-cc94-fd0c-dfa7-115ba8a6b95a@android.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <71d66fd1-cc94-fd0c-dfa7-115ba8a6b95a@android.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190815_083033_319488_063F2A38 X-CRM114-Status: GOOD ( 27.32 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Latchesar Ionkov , Dave Kleikamp , jfs-discussion@lists.sourceforge.net, Phillip Lougher , Jan Kara , linux-integrity@vger.kernel.org, Martin Brandenburg , samba-technical@lists.samba.org, Dominique Martinet , Chao Yu , Mimi Zohar , Adrian Hunter , linux-mm@kvack.org, Chris Mason , netdev@vger.kernel.org, Andreas Dilger , linux-xfs@vger.kernel.org, Eric Paris , linux-f2fs-devel@lists.sourceforge.net, linux-afs@lists.infradead.org, Stephen Smalley , Mike Marshall , devel@driverdev.osuosl.org, linux-cifs@vger.kernel.org, Paul Moore , Sage Weil , "Darrick J. Wong" , Richard Weinberger , Mark Fasheh , linux-unionfs@vger.kernel.org, Hugh Dickins , James Morris , cluster-devel@redhat.com, Joseph Qi , Vyacheslav Dubeyko , Casey Schaufler , v9fs-developer@lists.sourceforge.net, Ilya Dryomov , linux-ext4@vger.kernel.org, kernel-team@android.com, devel@lists.orangefs.org, Serge Hallyn , Gao Xiang , Eric Van Hensbergen , ecryptfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, Josef Bacik , reiserfs-devel@vger.kernel.org, Bob Peterson , Joel Becker , Anna Schumaker , David Sterba , Jaegeuk Kim , ceph-devel@vger.kernel.org, selinux@vger.kernel.org, Trond Myklebust , Andreas Gruenbacher , David Howells , linux-nfs@vger.kernel.org, Theodore Ts'o , linux-fsdevel@vger.kernel.org, Artem Bityutskiy , Mathieu Malaterre , Greg Kroah-Hartman , Miklos Szeredi , Jeff Layton , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Tyler Hicks , Steve French , Ernesto =?iso-8859-1?Q?A=2E_Fern=E1ndez?= , linux-btrfs@vger.kernel.org, linux-security-module@vger.kernel.org, Jan Kara , Tejun Heo , linux-mtd@lists.infradead.org, Andrew Morton , David Woodhouse , "David S. Miller" , ocfs2-devel@oss.oracle.com, Alexander Viro Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org On Wed 14-08-19 07:54:16, Mark Salyzyn wrote: > On 8/14/19 4:00 AM, Jan Kara wrote: > > On Tue 13-08-19 07:55:06, Mark Salyzyn wrote: > > ... > > > diff --git a/fs/xattr.c b/fs/xattr.c > > > index 90dd78f0eb27..71f887518d6f 100644 > > > --- a/fs/xattr.c > > > +++ b/fs/xattr.c > > ... > > > ssize_t > > > __vfs_getxattr(struct dentry *dentry, struct inode *inode, const char *name, > > > - void *value, size_t size) > > > + void *value, size_t size, int flags) > > > { > > > const struct xattr_handler *handler; > > > - > > > - handler = xattr_resolve_name(inode, &name); > > > - if (IS_ERR(handler)) > > > - return PTR_ERR(handler); > > > - if (!handler->get) > > > - return -EOPNOTSUPP; > > > - return handler->get(handler, dentry, inode, name, value, size); > > > -} > > > -EXPORT_SYMBOL(__vfs_getxattr); > > > - > > > -ssize_t > > > -vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size) > > > -{ > > > - struct inode *inode = dentry->d_inode; > > > int error; > > > + if (flags & XATTR_NOSECURITY) > > > + goto nolsm; > > Hum, is it OK for XATTR_NOSECURITY to skip even the xattr_permission() > > check? I understand that for reads of security xattrs it actually does not > > matter in practice but conceptually that seems wrong to me as > > XATTR_NOSECURITY is supposed to skip just security-module checks to avoid > > recursion AFAIU. > > Good catch I think. > > I was attempting to make this change purely inert, no change in > functionality, only a change in API. Adding a call to xattr_permission would > incur a change in overall functionality, as it would introduce into the > current and original __vfs_getxattr a call to xattr_permission that was not > there before. > > (I will have to defer the real answer and requirements to the security > folks) > > AFAIK you are correct, and to make the call would reduce the attack surface, > trading a very small amount of CPU utilization, for a much larger amount of > trust. > > Given the long history of this patch set (for overlayfs) and the large > amount of stakeholders, I would _prefer_ to submit a followup independent > functionality/security change to _vfs_get_xattr _after_ this makes it in. You're right. The problem was there before. So ack to changing this later. > > > diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h > > > index c1395b5bd432..1216d777d210 100644 > > > --- a/include/uapi/linux/xattr.h > > > +++ b/include/uapi/linux/xattr.h > > > @@ -17,8 +17,9 @@ > > > #if __UAPI_DEF_XATTR > > > #define __USE_KERNEL_XATTR_DEFS > > > -#define XATTR_CREATE 0x1 /* set value, fail if attr already exists */ > > > -#define XATTR_REPLACE 0x2 /* set value, fail if attr does not exist */ > > > +#define XATTR_CREATE 0x1 /* set value, fail if attr already exists */ > > > +#define XATTR_REPLACE 0x2 /* set value, fail if attr does not exist */ > > > +#define XATTR_NOSECURITY 0x4 /* get value, do not involve security check */ > > > #endif > > It seems confusing to export XATTR_NOSECURITY definition to userspace when > > that is kernel-internal flag. I'd just define it in include/linux/xattr.h > > somewhere from the top of flags space (like 0x40000000). > > > > Otherwise the patch looks OK to me (cannot really comment on the security > > module aspect of this whole thing though). > > Good point. However, we do need to keep these flags together to reduce > maintenance risk, I personally abhor two locations for flags bits even if > one comes from the opposite bit-side; collisions are undetectable at build > time. Although I have not gone through the entire thought experiment, I am > expecting that fuse could possibly benefit from this flag (if exposed) since > it also has a security recursion. That said, fuse is probably the example of > a gaping wide attack surface if user space had access to it ... your > xattr_permissions call addition requested above would be realistically, not > just pedantically, required! Yeah, flags bits in two places are bad as well. So maybe at least #ifdef __KERNEL__ bit around the definitiona and a comment that it is kernel internal flag? Honza -- Jan Kara SUSE Labs, CR ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/