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=-6.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH,URIBL_BLOCKED,USER_AGENT_GIT 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 18163C072B1 for ; Thu, 30 May 2019 03:39:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E417724BA8 for ; Thu, 30 May 2019 03:39:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559187574; bh=nGAUJRbLvnG4RZXmH6VU4fSaW9467h2MfLvkpldJnBI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=z2FmyuvVs0++zLyxdgGiwUVDhTYr8+gvy+XE5Q0tcTSrvEoCVcxkCuxfwCMYCn5+J GJv9zlWpwba4vPBu6t7ZeDpD9Uw2j3bISvVpFTLv+gxehbXYhXrhhf/i4a9dNGNohd AxQ9ki+gL8OrNAdZ45oul5g53N5NSUuN9u4M2sq4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732705AbfE3DWM (ORCPT ); Wed, 29 May 2019 23:22:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:43122 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729790AbfE3DQf (ORCPT ); Wed, 29 May 2019 23:16:35 -0400 Received: from localhost (ip67-88-213-2.z213-88-67.customer.algx.net [67.88.213.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 82D9924605; Thu, 30 May 2019 03:16:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559186194; bh=nGAUJRbLvnG4RZXmH6VU4fSaW9467h2MfLvkpldJnBI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gc3UOaGbM6UXSTDYf8D8QXHRuybzTcwE6UviYsnXY2x4hlIsh2B83ex9jPq7nswqQ VfbkMmFA0rOLw3hXk9lcEBPe1RY+8rY73APrihH8mc/5QFUhhz7e9Gq4XWLPmAHo36 9wYZC0dtKB41nRFPW/S/7bNdBurYFicGzXw8tc5o= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+9c69c282adc4edd2b540@syzkaller.appspotmail.com, Amir Goldstein , Miklos Szeredi Subject: [PATCH 4.19 032/276] ovl: relax WARN_ON() for overlapping layers use case Date: Wed, 29 May 2019 20:03:10 -0700 Message-Id: <20190530030526.260586516@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190530030523.133519668@linuxfoundation.org> References: <20190530030523.133519668@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Amir Goldstein commit acf3062a7e1ccf67c6f7e7c28671a6708fde63b0 upstream. This nasty little syzbot repro: https://syzkaller.appspot.com/x/repro.syz?x=12c7a94f400000 Creates overlay mounts where the same directory is both in upper and lower layers. Simplified example: mkdir foo work mount -t overlay none foo -o"lowerdir=.,upperdir=foo,workdir=work" The repro runs several threads in parallel that attempt to chdir into foo and attempt to symlink/rename/exec/mkdir the file bar. The repro hits a WARN_ON() I placed in ovl_instantiate(), which suggests that an overlay inode already exists in cache and is hashed by the pointer of the real upper dentry that ovl_create_real() has just created. At the point of the WARN_ON(), for overlay dir inode lock is held and upper dir inode lock, so at first, I did not see how this was possible. On a closer look, I see that after ovl_create_real(), because of the overlapping upper and lower layers, a lookup by another thread can find the file foo/bar that was just created in upper layer, at overlay path foo/foo/bar and hash the an overlay inode with the new real dentry as lower dentry. This is possible because the overlay directory foo/foo is not locked and the upper dentry foo/bar is in dcache, so ovl_lookup() can find it without taking upper dir inode shared lock. Overlapping layers is considered a wrong setup which would result in unexpected behavior, but it shouldn't crash the kernel and it shouldn't trigger WARN_ON() either, so relax this WARN_ON() and leave a pr_warn() instead to cover all cases of failure to get an overlay inode. The error returned from failure to insert new inode to cache with inode_insert5() was changed to -EEXIST, to distinguish from the error -ENOMEM returned on failure to get/allocate inode with iget5_locked(). Reported-by: syzbot+9c69c282adc4edd2b540@syzkaller.appspotmail.com Fixes: 01b39dcc9568 ("ovl: use inode_insert5() to hash a newly...") Signed-off-by: Amir Goldstein Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman --- fs/overlayfs/dir.c | 2 +- fs/overlayfs/inode.c | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-) --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -260,7 +260,7 @@ static int ovl_instantiate(struct dentry * hashed directory inode aliases. */ inode = ovl_get_inode(dentry->d_sb, &oip); - if (WARN_ON(IS_ERR(inode))) + if (IS_ERR(inode)) return PTR_ERR(inode); } else { WARN_ON(ovl_inode_real(inode) != d_inode(newdentry)); --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -832,7 +832,7 @@ struct inode *ovl_get_inode(struct super int fsid = bylower ? oip->lowerpath->layer->fsid : 0; bool is_dir, metacopy = false; unsigned long ino = 0; - int err = -ENOMEM; + int err = oip->newinode ? -EEXIST : -ENOMEM; if (!realinode) realinode = d_inode(lowerdentry); @@ -917,6 +917,7 @@ out: return inode; out_err: + pr_warn_ratelimited("overlayfs: failed to get inode (%i)\n", err); inode = ERR_PTR(err); goto out; }