From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: [PATCH review 1/7] dcache: Handle escaped paths in prepend_path Date: Sat, 15 Aug 2015 13:36:12 -0500 Message-ID: <874mk0761v.fsf_-_@x220.int.ebiederm.org> References: <871tncuaf6.fsf@x220.int.ebiederm.org> <87mw5xq7lt.fsf@x220.int.ebiederm.org> <87a8yqou41.fsf_-_@x220.int.ebiederm.org> <874moq9oyb.fsf_-_@x220.int.ebiederm.org> <871tfkawu9.fsf_-_@x220.int.ebiederm.org> <87egjk9i61.fsf_-_@x220.int.ebiederm.org> <20150810043637.GC14139@ZenIV.linux.org.uk> <877foymrwt.fsf@x220.int.ebiederm.org> <87wpwyjxwc.fsf_-_@x220.int.ebiederm.org> <87fv3mjxsc.fsf_-_@x220.int.ebiederm.org> <20150815061617.GG14139@ZenIV.linux.org.uk> <874mk08l3g.fsf@x220.int.ebiederm.org> <87a8ts763c.fsf_-_@x220.int.ebiederm.org> Mime-Version: 1.0 Content-Type: text/plain Cc: linux-fsdevel@vger.kernel.org, Al Viro , Andy Lutomirski , "Serge E. Hallyn" , Richard Weinberger , Andrey Vagin , Jann Horn , Willy Tarreau , Omar Sandoval , Miklos Szeredi , Linus Torvalds , "J. Bruce Fields" To: Linux Containers Return-path: Received: from out01.mta.xmission.com ([166.70.13.231]:56390 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754089AbbHOSnF (ORCPT ); Sat, 15 Aug 2015 14:43:05 -0400 In-Reply-To: <87a8ts763c.fsf_-_@x220.int.ebiederm.org> (Eric W. Biederman's message of "Sat, 15 Aug 2015 13:35:19 -0500") Sender: linux-fsdevel-owner@vger.kernel.org List-ID: A rename can result in a dentry that by walking up d_parent will never reach it's mnt_root. For lack of a better term I call this an escaped path. prepend_path is called by four different functions __d_path, d_absolute_path, d_path, and getcwd. __d_path only wants to see paths are connected to the root it passes in. So __d_path needs prepend_path to return an error. d_absolute_path similarly wants to see paths that are connected to some root. Escaped paths are not connected to any mnt_root so d_absolute_path needs prepend_path to return an error greater than 1. So escaped paths will be treated like paths on lazily unmounted mounts. getcwd needs to prepend "(unreachable)" so getcwd also needs prepend_path to return an error. d_path is the interesting hold out. d_path just wants to print something, and does not care about the weird cases. Which raises the question what should be printed? Given that / should result in -ENOENT I believe it is desirable for escaped paths to be printed as empty paths. As there are not really any meaninful path components when considered from the perspective of a mount tree. So tweak prepend_path to return an empty path with an new error code of 3 when it encounters an escaped path. Signed-off-by: "Eric W. Biederman" --- fs/dcache.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/dcache.c b/fs/dcache.c index 7a3f3e5f9cea..f762e76e85cc 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2923,6 +2923,13 @@ restart: if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) { struct mount *parent = ACCESS_ONCE(mnt->mnt_parent); + /* Escaped? */ + if (dentry != vfsmnt->mnt_root) { + bptr = *buffer; + blen = *buflen; + error = 3; + break; + } /* Global root? */ if (mnt != parent) { dentry = ACCESS_ONCE(mnt->mnt_mountpoint); -- 2.2.1