Re: Does anyone care about a race free ptsname?

[Eric W. Biederman]

"H. Peter Anvin" <hpa@xxxxxxxxx> writes:

> We could add another ioctl for that purpose of we need to.  Perhaps an
> ioctl which returns a file descriptor to the slave device?
>
> However, since we are now defining ptmx to explicitly look up pts/ by
> name it seems like /dev/ptmx -> /dev/pts/# is true by definition.  If
> what you worry about is namespace reshuffling then ptsname() is the
> wrong interface in the first place since it returns a pathname.

Good point.  Yes if we are not using devpts_mnt (hooray!) there should
be no complications, and the largest check we would need is to verify
that /dev/ptmx is in the current namespace.

> Fwiw, in klibc ptsname() is basically just an sprintf().

The challenge came in operations such as granpt.  Where you are passed
in a ptmx file descriptor from who knows where, and you pass it on
to applications such as pt_chown which run with elevatated privileged.

As the information is available of where devpts is mounted in
relationship to /dev/ptmx I have no more concerns about implementing
ptsname.  Path pased is also sufficiently backwards compatible it would
not usually be wrong even on existing kernels.

Good enough.

Eric