Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751281AbWHSQtS (ORCPT ); Sat, 19 Aug 2006 12:49:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751371AbWHSQtS (ORCPT ); Sat, 19 Aug 2006 12:49:18 -0400 Received: from smtp.osdl.org ([65.172.181.4]:14488 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1751281AbWHSQtR (ORCPT ); Sat, 19 Aug 2006 12:49:17 -0400 Date: Sat, 19 Aug 2006 09:48:40 -0700 From: Andrew Morton To: David Howells Cc: Trond Myklebust , linux-kernel@vger.kernel.org, aviro@redhat.com, Ian Kent Subject: Re: [PATCH] NFS: Replace null dentries that appear in readdir's list [try #2] Message-Id: <20060819094840.083026fd.akpm@osdl.org> In-Reply-To: <2138.1155893924@warthog.cambridge.redhat.com> References: <13319.1155744959@warthog.cambridge.redhat.com> <1155743399.5683.13.camel@localhost> <20060813133935.b0c728ec.akpm@osdl.org> <20060813012454.f1d52189.akpm@osdl.org> <5910.1155741329@warthog.cambridge.redhat.com> <2138.1155893924@warthog.cambridge.redhat.com> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.17; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2549 Lines: 65 On Fri, 18 Aug 2006 10:38:44 +0100 David Howells wrote: > NFS: Replace null dentries that appear in readdir's list [try #2] > > 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). > The funny-looking dentries in /net/bix have gone away. But `ls -l /net/bix/usr/src' doesn't mount bix:/usr/src. - 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/