Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261684AbVEUH1Q (ORCPT ); Sat, 21 May 2005 03:27:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261690AbVEUH1Q (ORCPT ); Sat, 21 May 2005 03:27:16 -0400 Received: from e33.co.us.ibm.com ([32.97.110.131]:50864 "EHLO e33.co.us.ibm.com") by vger.kernel.org with ESMTP id S261684AbVEUH0w (ORCPT ); Sat, 21 May 2005 03:26:52 -0400 Subject: Re: [RFC][PATCH] rbind across namespaces From: Ram To: Miklos Szeredi Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , viro@parcelfarce.linux.theplanet.co.uk, jamie@shareable.org In-Reply-To: References: <1116627099.4397.43.camel@localhost> Content-Type: multipart/mixed; boundary="=-S09cCfwaXfZJikH7iXvy" Organization: IBM Message-Id: <1116660380.4397.66.camel@localhost> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.6 Date: Sat, 21 May 2005 00:26:20 -0700 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4370 Lines: 152 --=-S09cCfwaXfZJikH7iXvy Content-Type: text/plain Content-Transfer-Encoding: 7bit On Fri, 2005-05-20 at 23:27, Miklos Szeredi wrote: > > I have enclosed a patch that allows rbinds across any two namespaces. > > NOTE: currenly bind from foriegn namespace to current namespace is > > allowed. This patch now allows: > > Note: you are accessing ->mnt_namespace without holding vfsmount_lock. I realized that just after sending the patch :( . Have corrected it in the new patch. > > Also why check current->namespace? It doesn't hurt to do > get_namespace() even if it's not strictly needed. And it would > simplify the code. however get_namespace() will chew up some extra cycles sometimes unnecessarily. I did incorporate your comment and got much simpler code. > > In fact all uses of current->namespace and check_mnt() could be > eliminated from namespace.c. The only use of ->namespace would be in > copy_namespace() and exit_namespace(). Yes. I will make this a separate patch, which I will send out soon. Will have to look at each of the cases deeply. Enclosed the simplified patch, RP --=-S09cCfwaXfZJikH7iXvy Content-Disposition: attachment; filename=rbind_across_namespace1.patch Content-Type: text/x-patch; name=rbind_across_namespace1.patch Content-Transfer-Encoding: 7bit Summary: Allows rbinds across any two namespaces. NOTE: currenly bind from foriegn namespace to current namespace is allowed. This patch now allows: binds/rbinds from any namespace to any other namespace, under the assumption that if a process has access to a namespace, it ought to have permission to manipulate that namespace. The patch incorporates ideas from Miklos and Jamie, and is dependent on Miklos's "fix race in mark_mounts_for_expiry" patch to function correctly. Also it depends on Miklos's "fix bind mount from foreign namespace" patch, because without that patch umounts would fail. Signed off by Ram Pai --- /home/linux/views/linux-2.6.12-rc4/fs/namespace.c 2005-05-06 23:22:29.000000000 -0700 +++ linux-2.6.12-rc4/fs/namespace.c 2005-05-21 00:17:31.000000000 -0700 @@ -616,11 +616,14 @@ out_unlock: } /* - * do loopback mount. + * do loopback mount. The loopback mount can be done from any namespace + * to any other namespace including the current namespace, as long as + * the task acquired rights to manipulate them. */ static int do_loopback(struct nameidata *nd, char *old_name, int recurse) { struct nameidata old_nd; + struct namespace *mntpt_ns, *old_ns; struct vfsmount *mnt = NULL; int err = mount_is_safe(nd); if (err) @@ -631,16 +634,39 @@ static int do_loopback(struct nameidata if (err) return err; - down_write(¤t->namespace->sem); err = -EINVAL; - if (check_mnt(nd->mnt) && (!recurse || check_mnt(old_nd.mnt))) { - err = -ENOMEM; - if (recurse) - mnt = copy_tree(old_nd.mnt, old_nd.dentry); - else - mnt = clone_mnt(old_nd.mnt, old_nd.dentry); + spin_lock(&vfsmount_lock); + + mntpt_ns = nd->mnt->mnt_namespace; + old_ns = old_nd.mnt->mnt_namespace; + if (!mntpt_ns || !mntpt_ns->root || !old_ns || !old_ns->root) { + spin_unlock(&vfsmount_lock); + goto out; + } + get_namespace(mntpt_ns); + get_namespace(old_ns); + + spin_unlock(&vfsmount_lock); + + /* + * make sure we don't race with some + * other thread manipulating the + * namespaces. + */ + if (old_ns < mntpt_ns) { + down_write(&old_ns->sem); + } + down_write(&mntpt_ns->sem); + if (old_ns > mntpt_ns) { + down_write(&old_ns->sem); } + err = -ENOMEM; + if (recurse) + mnt = copy_tree(old_nd.mnt, old_nd.dentry); + else + mnt = clone_mnt(old_nd.mnt, old_nd.dentry); + if (mnt) { /* stop bind mounts from expiring */ spin_lock(&vfsmount_lock); @@ -656,7 +682,17 @@ static int do_loopback(struct nameidata mntput(mnt); } - up_write(¤t->namespace->sem); + if (old_ns < mntpt_ns) { + up_write(&old_ns->sem); + } + up_write(&mntpt_ns->sem); + if (old_ns > mntpt_ns) { + up_write(&old_ns->sem); + } + + put_namespace(old_ns); + put_namespace(mntpt_ns); +out: path_release(&old_nd); return err; } --=-S09cCfwaXfZJikH7iXvy-- - 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/