Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751208AbWHPPPo (ORCPT ); Wed, 16 Aug 2006 11:15:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751196AbWHPPPo (ORCPT ); Wed, 16 Aug 2006 11:15:44 -0400 Received: from mx1.redhat.com ([66.187.233.31]:45195 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S1751208AbWHPPPn (ORCPT ); Wed, 16 Aug 2006 11:15:43 -0400 From: David Howells In-Reply-To: <20060813133935.b0c728ec.akpm@osdl.org> References: <20060813133935.b0c728ec.akpm@osdl.org> <20060813012454.f1d52189.akpm@osdl.org> To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Trond Myklebust , aviro@redhat.com, David Howells , Ian Kent Subject: [PATCH] NFS: Revalidate on readdir referring to null dentry X-Mailer: MH-E 8.0; nmh 1.1; GNU Emacs 22.0.50 Date: Wed, 16 Aug 2006 16:15:29 +0100 Message-ID: <5910.1155741329@warthog.cambridge.redhat.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4305 Lines: 127 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) { + 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/