Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932088AbWHPPuW (ORCPT ); Wed, 16 Aug 2006 11:50:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932089AbWHPPuW (ORCPT ); Wed, 16 Aug 2006 11:50:22 -0400 Received: from pat.uio.no ([129.240.10.4]:40345 "EHLO pat.uio.no") by vger.kernel.org with ESMTP id S932088AbWHPPuV (ORCPT ); Wed, 16 Aug 2006 11:50:21 -0400 Subject: Re: [PATCH] NFS: Revalidate on readdir referring to null dentry From: Trond Myklebust To: David Howells Cc: Andrew Morton , linux-kernel@vger.kernel.org, aviro@redhat.com, Ian Kent In-Reply-To: <5910.1155741329@warthog.cambridge.redhat.com> References: <20060813133935.b0c728ec.akpm@osdl.org> <20060813012454.f1d52189.akpm@osdl.org> <5910.1155741329@warthog.cambridge.redhat.com> Content-Type: text/plain Date: Wed, 16 Aug 2006 11:49:59 -0400 Message-Id: <1155743399.5683.13.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.6.1 Content-Transfer-Encoding: 7bit X-UiO-Spam-info: not spam, SpamAssassin (score=-1.975, 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: 5065 Lines: 145 On Wed, 2006-08-16 at 16:15 +0100, David Howells wrote: > Andrew Morton wrote: > > > This kernel breaks autofs /net handling. Bisection shows that the bug is > > introduced by git-nfs.patch. > > Does this patch fix your problem? > > David > --- > NFS: Revalidate on readdir referring to null dentry > > From: David Howells > > Have nfs_readdir_lookup() force dentry revalidation when it comes across a > name specified by a READDIR RPC call that corresponds to a negative dentry in > the dcache. > > 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) cause a revalidation to occur on the dentry at the > start of step (9). > > Signed-Off-By: David Howells > --- > > fs/nfs/dir.c | 16 +++++++++++++++- > include/linux/dcache.h | 5 +++++ > 2 files changed, 20 insertions(+), 1 deletions(-) > > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c > index e746ed1..901b382 100644 > --- a/fs/nfs/dir.c > +++ b/fs/nfs/dir.c > @@ -745,6 +745,13 @@ static int nfs_lookup_revalidate(struct > nfs_inc_stats(dir, NFSIOS_DENTRYREVALIDATE); > inode = dentry->d_inode; > > + if (dentry->d_flags & DCACHE_NEED_REVALIDATE) { This flag is redundant. There already exist methods for determining if a dentry needs revalidation by means of the nfs_*_verifier() functions. If you want to force a dentry lookup upon next revalidation, then add something like void nfs_dentry_force_revalidate(struct inode *dir, struct dentry *dentry) { nfs_set_verifier(dentry, nfs_save_change_attribute(dir) - 1); } Better still, in the case of a negative dentry: just call d_drop(). Cheers, Trond > + spin_lock(&dentry->d_lock); > + dentry->d_flags &= ~DCACHE_NEED_REVALIDATE; > + spin_unlock(&dentry->d_lock); > + goto out_bad; > + } > + > if (!inode) { > if (nfs_neg_need_reval(dir, dentry, nd)) > goto out_bad; > @@ -1105,8 +1112,15 @@ static struct dentry *nfs_readdir_lookup > } > name.hash = full_name_hash(name.name, name.len); > dentry = d_lookup(parent, &name); > - if (dentry != NULL) > + if (dentry != NULL) { > + /* negative dentries must be reconsidered */ > + if (!IS_ERR(dentry) && !dentry->d_inode) { > + spin_lock(&dentry->d_lock); > + dentry->d_flags |= DCACHE_NEED_REVALIDATE; > + spin_unlock(&dentry->d_lock); > + } > return dentry; > + } > if (!desc->plus || !(entry->fattr->valid & NFS_ATTR_FATTR)) > return NULL; > /* Note: caller is already holding the dir->i_mutex! */ > diff --git a/include/linux/dcache.h b/include/linux/dcache.h > index 63f64a9..c401a7d 100644 > --- a/include/linux/dcache.h > +++ b/include/linux/dcache.h > @@ -176,6 +176,11 @@ #define DCACHE_UNHASHED 0x0010 > > #define DCACHE_INOTIFY_PARENT_WATCHED 0x0020 /* Parent inode is watched */ > > +#define DCACHE_NEED_REVALIDATE 0x0040 > + /* Dentry needs revalidation by filesystem. Set by NFS, for example, > + * when we see in a directory listing a file for which we have a > + * negative dentry */ > + > extern spinlock_t dcache_lock; > > /** - 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/