* Theodore Ts'o (tytso@xxxxxxx) wrote: > On Wed, Jun 30, 2021 at 04:01:42PM +0100, Dr. David Alan Gilbert wrote: > > > > Even if you fix symlinks, I don't think it fixes device nodes or > > anything else where the permissions bitmap isn't purely used as the > > permissions on the inode. > > I think we're making a mountain out of a molehill. Again, very few > people are using quota these days. And if you give someone write > access to a 8TB disk, do you really care if they can "steal" 32k worth > of space (which is the maximum size of an xattr, enforced by the VFS). > > OK, but what about character mode devices? First of all, most users > don't have access to huge number of devices, but let's assume > something absurd. Let's say that a user has write access to *1024* > devices. (My /dev has 233 character mode devices, and I have write > access to well under a dozen.) > > An 8TB disk costs about $200. So how much of the "stolen" quota space > are we talking about, assuming the user has access to 1024 devices, > and the file system actually supports a 32k xattr. > > 32k * 1024 * $200 / 8TB / (1024*1024*1024) = $0.000763 = 0.0763 cents > > A 2TB SSD is less around $180, so even if we calculate the prices > based on SSD space, we're still talking about a quarter of a penny. > > Why are we worrying about this? I'm not worrying about storage cost, but we would need to define what the rules are on who can write and change a user.* xattr on a device node. It doesn't feel sane to make it anyone who can write to the device; then everyone can start leaving droppings on /dev/null. The other evilness I can imagine, is if there's a 32k limit on xattrs on a node, an evil user could write almost 32k of junk to the node and then break the next login that tries to add an acl or breaks the next relabel. Dave > - Ted > -- Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK
