Re: [PATCH] linux ttyname and ttyname_r: return link if appropriate

["Serge E. Hallyn" <serge@hallyn.com>]

Quoting Dmitry V. Levin (ldv@altlinux.org):
> On Tue, Aug 09, 2016 at 04:39:37PM -0500, Serge E. Hallyn wrote:
> [...]
> > --- a/sysdeps/unix/sysv/linux/ttyname.c
> > +++ b/sysdeps/unix/sysv/linux/ttyname.c
> [...]
> > +      /* If the link doesn't exist, then it points to a device in another
> > +	 namespace.  If it is a UNIX98 pty, then return the /proc/self
> > +	 fd, as it points to a name unreachable in our namespace.  */
> > +      if (is_pty (&st) && strlen (procname) < buflen - 1)
> > +	return strcpy (ttyname_buf, procname);
> 
> With buflen == 4095 and sizeof(procname) == 30, this buflen check looks
> redundant.  To keep the safe side, I'd rather add a static assert instead,
> e.g.
> 
> #define TTYNAME_BUFLEN 4095
> ...
> buflen = TTYNAME_BUFLEN;
> ...
> _Static_assert (sizeof (procname) < TTYNAME_BUFLEN, "buflen too small");
> 
> [...]
> > --- a/sysdeps/unix/sysv/linux/ttyname_r.c
> > +++ b/sysdeps/unix/sysv/linux/ttyname_r.c
> [...]
> > +      /* If the link doesn't exist, then it points to a device in another
> > +	 namespace.  If it is a UNIX98 pty, then return the /proc/self
> > +	 fd, as it points to a name unreachable in our namespace.  */
> > +      if (is_pty (&st) && strlen (procname) < buflen - 1)
> > +	{
> > +	  strcpy (buf, procname);
> > +	  return 0;
> > +	}
> 
> Unlike ttyname.c, here buflen might be quite small, and this code skips
> strlen (procname) == buflen - 1.  Shouldn't it rather be
> strlen (procname) < buflen ?

Hm, yeah that's right.

> If is_pty(&st) is true but buflen is too small for procname, is there any
> chance of finding the device using getttyname_r?  Shouldn't ttyname_r fail
> with ERANGE instead?

So you mean

	if (is_pty (&st)) {
		if (strlen (procname) < buflen) {
			strcpy (buf, procname);
			return 0;
		}
		return -ERANGE;
	}

?