From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-3216147-1523476310-2-12612165404416585210 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.25, MAILING_LIST_MULTI -1, ME_NOAUTH 0.01, RCVD_IN_DNSWL_HI -5, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='US', FromHeader='org', MailFrom='org' X-Spam-charsets: plain='UTF-8' X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: stable-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=fm2; t= 1523476309; b=rCNlkaF12lTBdLZXFstLfVgzrrSES9ctp3EpYtLZ1dvoPN8zG6 eNFkoD0UYuUnZqGJB4FagCX9nri+58hQD2GFs/+8FtGX18ND7J7cTIvQi7dSuTgq N8iYStrA1tBhH5QWGdN+HYzKK7HxYXtmtSQ/zmrET5tHHdk4iL6FEa0+VGOQPqw5 mcMHwbU4xjhkrxfFZiJQH2v83H6W1OsGUfzr78x+ozjdb9hcEqUDKZxhIip3twBq JN+tDxIYJ9cOAs0BUG3dueDsh/01vsML2oeBa95qPgJRmqT2PB0I16YXFTY64cUJ ltuxcctmtofJQbyrv4/a05REYN2AvyCh5urQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=from:to:cc:subject:date:message-id :in-reply-to:references:mime-version:content-type:sender :list-id; s=fm2; t=1523476309; bh=EMiGmM6gOYJkj+M7JYzH2qHwkhe7WJ Ra/XDe/Y+sk0E=; b=WZoaNZWjjdt2MPJIhsc6NibbLIifayIMU22a2gikA2Os9s dxdiA7bHY86wHGuPQQFfpWuca0wwc0/oltL46MH2s0MAFmRVHqU0hVMksNY8weQR IoBU/WcU1isEiWAaUuj3Mwi35JccNbiv5fcU2zjO7J22WjtfKvbHv9XiRn+/ZhVB UXpAnPsnAVkJCpWH8qj8+8ME9gtnOqP7dP7UHtxtxs3IS5xp9gZ7YwFKBqWAZiN+ P7hm1UlZwl1qbyzTtgQVOAUHLxD5oQkTLlf7I+A5gJQ7Bt9rAT5NHVpCNSDWicru MxmveOZZe4QK9QLfWaRV/tHGMpesEblJJQo2TYxg== ARC-Authentication-Results: i=1; mx5.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=linuxfoundation.org; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-cm=none score=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=linuxfoundation.org header.result=pass header_is_org_domain=yes; x-vs=clean score=-100 state=0 Authentication-Results: mx5.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=linuxfoundation.org; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-cm=none score=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=linuxfoundation.org header.result=pass header_is_org_domain=yes; x-vs=clean score=-100 state=0 X-ME-VSCategory: clean X-CM-Envelope: MS4wfFEoWlfJdXF7CPaSRMuIMGAY8HpManOgRBtiVq9iLPS/Wzh0tKklyxx8wWSA6G0TaZmkI9oiwO3jusEfx7noTa1D3o0oCClorGGyuMtx1H/qy/mS7mhp 9s5yfpYjrYb8Fnmxbg/t8tcm9s3GzviIJaM0Pp0RhHxZy7Sc9Ora4VdVAW6qLyGVzliK33Y1mK3rlsfeA9zBYXwXc6RcczRj6NjpNCBTmGpAXkOUYlrJ6AdJ X-CM-Analysis: v=2.3 cv=NPP7BXyg c=1 sm=1 tr=0 a=UK1r566ZdBxH71SXbqIOeA==:117 a=UK1r566ZdBxH71SXbqIOeA==:17 a=IkcTkHD0fZMA:10 a=Kd1tUaAdevIA:10 a=iox4zFpeAAAA:8 a=QyXUC8HyAAAA:8 a=VwQbUJbxAAAA:8 a=drOt6m5kAAAA:8 a=yMhMjlubAAAA:8 a=ag1SF4gXAAAA:8 a=NB6CG2mJGxnl6YEIGE4A:9 a=QEXdDO2ut3YA:10 a=WzC6qhA0u3u7Ye7llzcV:22 a=AjGcO6oz07-iQ99wixmX:22 a=RMMjzBEyIzXRtoq5n5K6:22 a=Yupwre4RP9_Eg_Bd0iYG:22 X-ME-CMScore: 0 X-ME-CMCategory: none Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754386AbeDKS6U (ORCPT ); Wed, 11 Apr 2018 14:58:20 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36624 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755480AbeDKS6R (ORCPT ); Wed, 11 Apr 2018 14:58:17 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, NeilBrown , Al Viro , Sasha Levin Subject: [PATCH 4.9 128/310] VFS: close race between getcwd() and d_move() Date: Wed, 11 Apr 2018 20:34:27 +0200 Message-Id: <20180411183627.974360341@linuxfoundation.org> X-Mailer: git-send-email 2.17.0 In-Reply-To: <20180411183622.305902791@linuxfoundation.org> References: <20180411183622.305902791@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: NeilBrown [ Upstream commit 61647823aa920e395afcce4b57c32afb51456cab ] d_move() will call __d_drop() and then __d_rehash() on the dentry being moved. This creates a small window when the dentry appears to be unhashed. Many tests of d_unhashed() are made under ->d_lock and so are safe from racing with this window, but some aren't. In particular, getcwd() calls d_unlinked() (which calls d_unhashed()) without d_lock protection, so it can race. This races has been seen in practice with lustre, which uses d_move() as part of name lookup. See: https://jira.hpdd.intel.com/browse/LU-9735 It could race with a regular rename(), and result in ENOENT instead of either the 'before' or 'after' name. The race can be demonstrated with a simple program which has two threads, one renaming a directory back and forth while another calls getcwd() within that directory: it should never fail, but does. See: https://patchwork.kernel.org/patch/9455345/ We could fix this race by taking d_lock and rechecking when d_unhashed() reports true. Alternately when can remove the window, which is the approach this patch takes. ___d_drop() is introduce which does *not* clear d_hash.pprev so the dentry still appears to be hashed. __d_drop() calls ___d_drop(), then clears d_hash.pprev. __d_move() now uses ___d_drop() and only clears d_hash.pprev when not rehashing. Signed-off-by: NeilBrown Signed-off-by: Al Viro Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- fs/dcache.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -461,9 +461,11 @@ static void dentry_lru_add(struct dentry * d_drop() is used mainly for stuff that wants to invalidate a dentry for some * reason (NFS timeouts or autofs deletes). * - * __d_drop requires dentry->d_lock. + * __d_drop requires dentry->d_lock + * ___d_drop doesn't mark dentry as "unhashed" + * (dentry->d_hash.pprev will be LIST_POISON2, not NULL). */ -void __d_drop(struct dentry *dentry) +static void ___d_drop(struct dentry *dentry) { if (!d_unhashed(dentry)) { struct hlist_bl_head *b; @@ -479,12 +481,17 @@ void __d_drop(struct dentry *dentry) hlist_bl_lock(b); __hlist_bl_del(&dentry->d_hash); - dentry->d_hash.pprev = NULL; hlist_bl_unlock(b); /* After this call, in-progress rcu-walk path lookup will fail. */ write_seqcount_invalidate(&dentry->d_seq); } } + +void __d_drop(struct dentry *dentry) +{ + ___d_drop(dentry); + dentry->d_hash.pprev = NULL; +} EXPORT_SYMBOL(__d_drop); void d_drop(struct dentry *dentry) @@ -2378,7 +2385,7 @@ EXPORT_SYMBOL(d_delete); static void __d_rehash(struct dentry *entry) { struct hlist_bl_head *b = d_hash(entry->d_name.hash); - BUG_ON(!d_unhashed(entry)); + hlist_bl_lock(b); hlist_bl_add_head_rcu(&entry->d_hash, b); hlist_bl_unlock(b); @@ -2815,9 +2822,9 @@ static void __d_move(struct dentry *dent write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED); /* unhash both */ - /* __d_drop does write_seqcount_barrier, but they're OK to nest. */ - __d_drop(dentry); - __d_drop(target); + /* ___d_drop does write_seqcount_barrier, but they're OK to nest. */ + ___d_drop(dentry); + ___d_drop(target); /* Switch the names.. */ if (exchange) @@ -2829,6 +2836,8 @@ static void __d_move(struct dentry *dent __d_rehash(dentry); if (exchange) __d_rehash(target); + else + target->d_hash.pprev = NULL; /* ... and switch them in the tree */ if (IS_ROOT(dentry)) {