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

Quoting Serge Hallyn (serge.hallyn@ubuntu.com):
> Quoting Florian Weimer (fweimer@redhat.com):
> > 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.
> 
> Oh, yeah.  I think that adding a chck that this is a pts (using st_rdev)
> before returning "/proc/self/fd/N" (in my newly added block) would be good.

Something like:

From ba0dc51e90d884b107145924821a1e8caf43a468 Mon Sep 17 00:00:00 2001
From: Serge Hallyn <serge.hallyn@ubuntu.com>
Date: Fri, 15 Apr 2016 10:21:07 -0500
Subject: [PATCH 1/1] linux ttyname: return link if appropriate

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.

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.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
---
 sysdeps/unix/sysv/linux/ttyname.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

On 15 Apr 2016 18:47, Serge Hallyn wrote:
> Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>

we don't use s-o-b tags

> +/*
> + * Return true if this is a UNIX98 pty device, as defined in
> + * linux/Documentation/devices.txt
> + */

GNU style is:

/* Return true if this is a UNIX98 pty device, as defined in
   linux/Documentation/devices.txt.  */

this applies to comments below too

> +      if (is_pty (st) && strlen (procname) < buflen - 1)
> +        {
> +          memcpy (ttyname_buf, procname, strlen (procname));
> +          ttyname_buf[strlen (procname)] = '\0';

since you already verified buflen, why not use strcpy ?

also, GNU style says 8 spaces -> 1 tab
-mike

Quoting Mike Frysinger (vapier@gentoo.org):
> On 15 Apr 2016 18:47, Serge Hallyn wrote:
> > Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
> 
> we don't use s-o-b tags
> 
> > +/*
> > + * Return true if this is a UNIX98 pty device, as defined in
> > + * linux/Documentation/devices.txt
> > + */
> 
> GNU style is:
> 
> /* Return true if this is a UNIX98 pty device, as defined in
>    linux/Documentation/devices.txt.  */
> 
> this applies to comments below too
> 
> > +      if (is_pty (st) && strlen (procname) < buflen - 1)
> > +        {
> > +          memcpy (ttyname_buf, procname, strlen (procname));
> > +          ttyname_buf[strlen (procname)] = '\0';
> 
> since you already verified buflen, why not use strcpy ?

That actually had been my first inclination, not sure why I
switched it.

> also, GNU style says 8 spaces -> 1 tab
> -mike

There were a few other bugs as well.  Replying with a new patch.

thanks,
-serge