On Tue, Feb 16, 2010 at 02:32:05PM -0500, Christoph Hellwig wrote: > On Tue, Feb 16, 2010 at 02:25:40PM -0500, J. Bruce Fields wrote: > > It'd allow nfsd to implement export subtrees safely. > > > > (The current problem: there's not an easy way to determine whether an > > inode (looked up from a filehandle) is reachable from a given directory. > > So if you export a directory that isn't the root of a filesystem, you > > have an unfortunate choice: > > > > - turn on the "subtree_check" export option: add information > > sufficient to lookup the parent directory to each filehandle. > > But then filehandles change (and clients get ESTALE) on > > cross-directory rename. > > > > - Accept the possibility that someone could fake up a filehandle > > that grants access to files outside the exported subtree. OK > > if you're exporting the subtree just for convenience, but bad > > if you're exporting /usr/local and think /etc/some-secret is > > safe without /usr/local being on a separate partition. > > > > With subtrees presumably we could stick the subtree-id in the > > filehandle, and the subtree would provide a security boundary that's > > easy to check on filehandle lookup (by comparing the subtree-id in the > > filehandle to the one in the inode you find). And subtrees would be > > simpler to manage than separate partitions.) > > NFS exporting is in fact the reason why the XFS hierachial project > quotas were added, but only for space usage accounting and enforcement > reason. Adding the project ID to the file handles does indeed sound > like a good idea, I'll see if it's easily implementable. > > Note that in the end the best idea would be to simply allow mounting > multiple of these roots inside a single superblock. I lost you there. --b. > David Howell's > infrastructure for sharing a nfs superblock for multiple blocks > allows this, and I even implemented prototypes of this for ext2 and > xfs, and a rather mutilated version of my patches is still in btrfs. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
