Re: xattr names for unprivileged stacking?

Theodore Y. Ts'o
2020-08-31T14:23:39Z

On Sat, Aug 29, 2020 at 09:12:45PM +0100, Matthew Wilcox wrote:
> > 3) what happens to it if that underlying file is unlinked?
>
> Unlinking a file necessarily unlinks all the streams. So the file
> remains in existance until all fds on it are closed, including all
> the streams.

That's a bad idea, because if the fds are closed silently, then they
can be reused; and then if the userspace library tries to write to
what it *thinks* is an ADS file, not knowing that the application has
unlinked and closed the ADS file, user file data would be lost.

What we would want instead (if we want to pursue the madness of ADS,
which I don't), is something like the effects of a BSD-style revoke(2)
system call, which causes all attempts to operate on said file
descriptor to return an error and/or EOF after the fd has been
revoked.

- Ted