[PATCH] ioctl_tty.2: add TIOCGPTPEER documentation

[Aleksa Sarai]

> I've applied this patch, and then tweaked the wording a little. Could
> you please check the following text:
> 
>         TIOCGPTPEER    int flags
>                (since Linux 4.13) Given  a  file  descriptor  in  fd  that
>                refers  to  a  pseudoterminal  master, open (with the given
>                open(2)-style flags) and return a new file descriptor  that
>                refers to the peer pseudoterminal slave device.  This oper‐
>                ation can be performed regardless of whether  the  pathname
>                of  the  slave  device  is  accessible  through the calling
>                process's mount namespaces.
> 
>                Security-conscious programs interacting with namespaces may
>                wish  to  use  this  operation rather than open(2) with the
>                pathname returned by ptsname(3), and similar library  func‐
>                tions that have insecure APIs.

Yup, that sounds good.

> I also have a question on the last sentence: what are the "similar library
> functions that have insecure APIs"? It's not clear to me what you are
> referring to here.

There are a few posix_-style functions provided by glibc that are just 
wrappers around the open+ptsname combo that I mention earlier in the 
sentence (and thus are vulnerable to the same issue). But if you feel 
it's confusing you can feel free to drop it.

Thanks.

-- 
Aleksa Sarai
Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/