Messages in this thread Patch in this message | | | Subject | Re: [RFC][PATCH] rbind across namespaces | From | Ram <> | Date | Sat, 21 May 2005 03:07:53 -0700 |
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On Sat, 2005-05-21 at 02:09, Miklos Szeredi wrote: > > > I still see a problem: what if old_nd.mnt is already detached, and > > > bind is non-recursive. Now it fails with EINVAL, though it used to > > > work (and I think is very useful). > > > > I am not getting this comment. R u assuming that a detached mount > > will have NULL namespace? > > Yes. > > > If so I dont see it being the case. > > See this patch: > > http://marc.theaimsgroup.com/?l=linux-kernel&m=111627383207049&w=2
Ok. look at the enclosed patch. Does it look any better? The special casing for detached mounts ate up some brain cells and made the code less simpler.
RP 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 only case disallowed is a recursive bind to a detached mount.
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 <linuxram@us.ibm.com>
--- /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 02:58:48.000000000 -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) @@ -631,15 +634,41 @@ 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); + + /* + * Allow all kinds of binds and rbinds except + * recursive bind to a detached mount + */ + mntpt_ns = nd->mnt->mnt_namespace; + old_ns = old_nd.mnt->mnt_namespace; + if (!mntpt_ns || !mntpt_ns->root || + (recurse && (!old_ns || !old_ns->root))) { + spin_unlock(&vfsmount_lock); + goto out; } + get_namespace(mntpt_ns); + if (recurse && old_ns != mntpt_ns) + get_namespace(old_ns); + + spin_unlock(&vfsmount_lock); + + /* + * make sure we don't race with some other thread manipulating the + * namespaces. + */ + if (recurse && (old_ns < mntpt_ns)) + down_write(&old_ns->sem); + down_write(&mntpt_ns->sem); + if (recurse && (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 */ @@ -656,7 +685,14 @@ static int do_loopback(struct nameidata mntput(mnt); } - up_write(¤t->namespace->sem); + up_write(&mntpt_ns->sem); + if (recurse && (old_ns != mntpt_ns)) { + up_write(&old_ns->sem); + put_namespace(old_ns); + } + put_namespace(mntpt_ns); + +out: path_release(&old_nd); return err; } | |