[PATCH 1/1] linux ttyname: return link if appropriate

[Florian Weimer]

On 04/15/2016 06:46 PM, Serge Hallyn wrote:
> Quoting Florian Weimer (fweimer@redhat.com):
>> On 04/15/2016 05:29 PM, Serge Hallyn wrote:
>>> The current ttyname does the wrong thing in two cases:
>>>
>>> 1. If the passed-in link (say /proc/self/fd/0) points to a
>>> device, say /dev/pts/2, in a parent mount namespace, and a
>>> /dev/pts/2 exists (in a different devpts) in the current
>>> namespace, then it returns /dev/pts/2.  But /dev/pts/2 is
>>> NOT the current tty, it is a different file and device.
>>
>> Is this the first change?
>
> Right, it ensures that the filesystem of the two files is
> the same.
>
>>> 2. If the passed-in link (say /proc/self/fd/0) points to
>>> a device, say /dev/pts/2, in a parent mount namespace, and
>>> /dev/pts/2 does not exist in the current namespace, it
>>> returns success but an empty name.  As far as I can tell,
>>> there is no reason for it to not return /proc/self/fd/0.
>>> http://pubs.opengroup.org/onlinepubs/009695399/functions/ttyname.html
>>> does not say anything about not returning a link.
>>
>> Is it safe to drop the verification that ttyname ordinarily would do?
>
> Which verification do you mean exactly?

That the file descriptor actually belongs to a PTY device listed under 
/dev/pts.

>> ttyname_r will need a similar change.
>
> Oh, yeah, it will.

Please also fix the stylistic issues (GNU style requires a space in 
function calls, braces on their own lines etc.).

But I don't think we can make the change, considering the security 
implications.

Florian