A day and a half or so ago I wrote > I'm going to look at 5.2 to see how hard it looks to have > unmount(,MNT_FORCE) do string comparisons in the mount table instead > of a namei walk. There is the case of having two things mounted on > the same path, but that shouldn't be unsolvable.
I have a proof-of-concept implementation written in 5.2. I actually made it a separate flag, MNT_STRING, orthogonal to MNT_FORCE, with a flag, -s, to make umount(8) use it. It seems to work. If I artificially fake the NFS server going dead (by adding a host reject route for the client's IP on the server), a normal unmount wedges, but with MNT_STRING|MNT_FORCE it unmounts just fine. There are probably issues with it, since it's a new and relatively untested facility, but it may be useful as a starting point. This is now in my mutant 5.2 src tree. The commit diff is available from ftp.rodents-montreal.org, in /pub/mouse/git-unpacked/Mouse/netbsd-fork/5.2/src/diff/89a4f0d-a744955 (also available over HTTP, though when I look at that view it renders somewhat brokenly - I *think* this is just a rendering issue), in case anyone is interested. And, as always, the whole repo is clonable from git://git.rodents-montreal.org/Mouse/netbsd-fork/5.2/src as well. Rather than duplicate the hair involved in dealing with chroot views of mount paths, I just made it work only for non-chrooted processes. I consider it an admin tool for unusual situations, for which use case I think banning it in chroots is reasonable. (Without this, a nonprivileged chroot process can use it to probe non-chrooted mount-on names, by looking at the errno returned from unmount attempts, which is information leakage, albeit minor information leakage in most cases.) /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mo...@rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
