Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751157AbWHPQgH (ORCPT ); Wed, 16 Aug 2006 12:36:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751167AbWHPQgH (ORCPT ); Wed, 16 Aug 2006 12:36:07 -0400 Received: from pat.uio.no ([129.240.10.4]:15057 "EHLO pat.uio.no") by vger.kernel.org with ESMTP id S1751157AbWHPQgE (ORCPT ); Wed, 16 Aug 2006 12:36:04 -0400 Subject: Re: [PATCH] NFS: Replace null dentries that appear in readdir's list From: Trond Myklebust To: David Howells Cc: Andrew Morton , linux-kernel@vger.kernel.org, aviro@redhat.com, Ian Kent In-Reply-To: <13319.1155744959@warthog.cambridge.redhat.com> References: <1155743399.5683.13.camel@localhost> <20060813133935.b0c728ec.akpm@osdl.org> <20060813012454.f1d52189.akpm@osdl.org> <5910.1155741329@warthog.cambridge.redhat.com> <13319.1155744959@warthog.cambridge.redhat.com> Content-Type: text/plain Date: Wed, 16 Aug 2006 12:35:44 -0400 Message-Id: <1155746145.5683.36.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.6.1 Content-Transfer-Encoding: 7bit X-UiO-Spam-info: not spam, SpamAssassin (score=-1.979, required 12, autolearn=disabled, AWL 0.51, RCVD_IN_XBL 2.51, UIO_MAIL_IS_INTERNAL -5.00) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3412 Lines: 99 On Wed, 2006-08-16 at 17:15 +0100, David Howells wrote: > Trond Myklebust wrote: > > > Better still, in the case of a negative dentry: just call d_drop(). > > How about this then? Yup. That would do it. Cheers, Trond > David > --- > NFS: Replace null dentries that appear in readdir's list > > From: David Howells > > Have nfs_readdir_lookup() drop and replace any null dentry when it > that gets listed by a READDIR RPC call. > > This can be caused by an optimisation in nfs_lookup() that causes a dentry to > be incorrectly left as negative when mkdir() or similar is aborted by SELinux > mid-procedure. > > This can be triggered by mounting through autofs4 a server:/ NFS share for > which there are other exports available on that server. SELinux also has to > be turned on in enforcing mode to abort mid-flow the mkdir operation performed > by autofs4. > > The problematic sequence of events is this: > > (1) nfs_lookup() is called by sys_mkdirat() -> lookup_create() -> > __lookup_hash() with intent to create exclusively set in the nameidata: > > nd->flags == LOOKUP_CREATE > nd->intent.open.flags == O_EXCL > > (2) nfs_lookup() has an optimisation to avoid going to the server in this > case, presumably since the nfs_mkdir() op or whatever will deal with the > conflict. > > (3) nfs_lookup() returns successfully, leaving the dentry in a negative state, > but attached to the parent directory. > > (4) sys_mkdirat() calls vfs_mkdir() which calls may_create(). may_create() > checks that the directory has MAY_WRITE and MAY_EXEC permissions. > > (5) may_create() calls nfs_permission(), which grants permission. > > (6) may_create() calls security_inode_permission(), which calls SELinux, which > then _DENIES_ permission. > > (7) may_create() fails, and vfs_mkdir() then fails and sys_mkdirat() then > fails (as does sys_mkdir). > > _However_, the new dentry is left in the negative state, with no > consultation of the server. > > (8) The parent directory is listed, and the name of the new dentry is > returned. > > (9) stat on the new dentry fails (because it's negative), and "ls -l" returns > "?---------" as the file type and mode. > > This fix makes step (8) replace the dentry looked up in steps (1) - (3). > > Signed-Off-By: David Howells > --- > > fs/nfs/dir.c | 9 +++++++-- > 1 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c > index e746ed1..bb8b5f0 100644 > --- a/fs/nfs/dir.c > +++ b/fs/nfs/dir.c > @@ -1105,8 +1105,13 @@ static struct dentry *nfs_readdir_lookup > } > name.hash = full_name_hash(name.name, name.len); > dentry = d_lookup(parent, &name); > - if (dentry != NULL) > - return dentry; > + if (dentry != NULL) { > + /* negative dentries must be reconsidered */ > + if (!IS_ERR(dentry) && !dentry->d_inode) > + d_drop(dentry); > + else > + return dentry; > + } > if (!desc->plus || !(entry->fattr->valid & NFS_ATTR_FATTR)) > return NULL; > /* Note: caller is already holding the dir->i_mutex! */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/