From: Frank van Maarseveen Subject: Re: [PATCH] exportfs: fix incorrect EACCES in reconnect_path() Date: Sat, 3 May 2008 10:52:05 +0200 Message-ID: <20080503085205.GB26931@janus> References: <20080407184346.GF3305@fieldses.org> <20080409133639.GA9588@lst.de> <18454.45086.254692.412079@notabene.brown> <20080429163554.GE20420@fieldses.org> <20080429174004.GA28719@janus> <20080430174736.GB20377@fieldses.org> <20080502151646.GA5515@janus> <20080502153439.GC7376@infradead.org> <20080502155617.GD18401@fieldses.org> <1209744293.8294.19.camel@heimdal.trondhjem.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "J. Bruce Fields" , Christoph Hellwig , Frank van Maarseveen , Neil Brown , Christoph Hellwig , Linux NFS mailing list To: Trond Myklebust Return-path: Received: from frankvm.xs4all.nl ([80.126.170.174]:55364 "EHLO janus.localdomain" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751623AbYECIwI (ORCPT ); Sat, 3 May 2008 04:52:08 -0400 In-Reply-To: <1209744293.8294.19.camel-rJ7iovZKK19ZJLDQqaL3InhyD016LWXt@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, May 02, 2008 at 12:04:53PM -0400, Trond Myklebust wrote: > > On Fri, 2008-05-02 at 11:56 -0400, J. Bruce Fields wrote: > > On Fri, May 02, 2008 at 11:34:39AM -0400, Christoph Hellwig wrote: > > > On Fri, May 02, 2008 at 05:16:46PM +0200, Frank van Maarseveen wrote: > > > > A privileged process on an NFS client which drops privileges after using > > > > them to change the current working directory, will experience incorrect > > > > EACCES after an NFS server reboot. This problem can also occur after > > > > memory pressure on the server, particularly when the client side is > > > > quiet for some time. > > > > > > > > This patch removes the x-bit check during dentry tree reconstruction at > > > > the server by exportfs on behalf of nfsd. > > > > > > I'm still against adding this crap, > > > > The only statements I've seen against the change so far have been of the > > form "you should not do that", without explaining why not. > > > > It's entirely possible that you're right, but I need some argument. > > > AFAICS, the real problem here is that nfsd is dropping its privileged > mode too early. Why can't you call reconnect_path() using nfsd's root > permissions instead of dropping permissions checks altogether? > > > > and even when I get overruled that > > > doesn't make the comments on lookup_one_noperm any less true, > > > > We do need to at least update it to reflect the addition of a new > > caller. > > > > > not does it give you a permit to break the kerneldoc generation. > > > > Oops; here's a version that should make kerneldoc happy. It also adds a > > little more explanation, and leaves alone the editorializing on sysfs > > (on which I have no opinion). > > > > --b. > > > > commit ccdfe77dc49a07c298bb9e2107290267492f16b3 > > Author: Frank van Maarseveen > > Date: Fri May 2 17:16:46 2008 +0200 > > > > exportfs: fix incorrect EACCES in reconnect_path() > > > > A privileged process on an NFS client which drops privileges after using > > them to change the current working directory, will experience incorrect > > EACCES after an NFS server reboot. This problem can also occur after > > memory pressure on the server, particularly when the client side is > > quiet for some time. > > > > This patch removes the x-bit check during dentry tree reconstruction at > > the server by exportfs on behalf of nfsd. > > > > Signed-off-by: Frank van Maarseveen > > Signed-off-by: J. Bruce Fields > > > > diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c > > index 109ab5e..89dc7ae 100644 > > --- a/fs/exportfs/expfs.c > > +++ b/fs/exportfs/expfs.c > > @@ -170,7 +170,7 @@ reconnect_path(struct vfsmount *mnt, struct dentry *target_dir) > > } > > dprintk("%s: found name: %s\n", __FUNCTION__, nbuf); > > mutex_lock(&ppd->d_inode->i_mutex); > > - npd = lookup_one_len(nbuf, ppd, strlen(nbuf)); > > + npd = lookup_one_noperm(nbuf, ppd); > > mutex_unlock(&ppd->d_inode->i_mutex); > > if (IS_ERR(npd)) { > > err = PTR_ERR(npd); > > @@ -447,8 +447,7 @@ struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid, > > err = exportfs_get_name(mnt, target_dir, nbuf, result); > > if (!err) { > > mutex_lock(&target_dir->d_inode->i_mutex); > > - nresult = lookup_one_len(nbuf, target_dir, > > - strlen(nbuf)); > > + nresult = lookup_one_noperm(nbuf, target_dir); > > mutex_unlock(&target_dir->d_inode->i_mutex); > > if (!IS_ERR(nresult)) { > > if (nresult->d_inode) { > > diff --git a/fs/namei.c b/fs/namei.c > > index e179f71..c00150c 100644 > > --- a/fs/namei.c > > +++ b/fs/namei.c > > @@ -1391,7 +1391,7 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) > > } > > > > /** > > - * lookup_one_noperm - bad hack for sysfs > > + * lookup_one_noperm - bad hack for sysfs and nfsd > > * @name: pathname component to lookup > > * @base: base directory to lookup from > > * > > @@ -1399,7 +1399,12 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) > > * checks. It's a horrible hack to work around the braindead sysfs > > * architecture and should not be used anywhere else. > > * > > - * DON'T USE THIS FUNCTION EVER, thanks. > > + * It is also used by nfsd via exports to reconstruct the dentry tree > > + * for directory handles (e.g. when a client requests a directory by > > + * filehandle after a server reboot has cleared the dentry cache of that > > + * directory's parents). > > + * > > + * DON'T USE THIS FUNCTION ANYWHERE ELSE, thanks. > > */ > > struct dentry *lookup_one_noperm(const char *name, struct dentry *base) > > { > > How about if exportfs is compiled as a module? Good point. The patch should include a EXPORT_SYMBOL(lookup_one_noperm) in fs/namei.c if we decide to fix it this way. -- Frank