Re: [Qemu-devel] pty/tty functions for BSD too

[Daniel P. Berrange]

On Mon, Aug 18, 2008 at 09:08:50PM +0300, Blue Swirl wrote:
> On 8/18/08, Blue Swirl <address@hidden> wrote:
> > On 8/18/08, Daniel P. Berrange <address@hidden> wrote:
> >  >
> >  >  [quote openpty(1)]
> >  >  BUGS
> >  >        Nobody knows how much space should be reserved for name.  So, 
> > call-
> >  >        ing openpty() or forkpty() with non-NULL name may not be secure.
> >  >  [/quote]
> >
> >
> > Maybe in theory, but in practice the name will be
> >  /dev/pty[0-9a-z][a-z] or /dev/pts/[0-9]* or something similar. Even if
> >  they are not, PATH_MAX should be enough.
> >
> >
> >  >  If BSD has no other way to determine the PTY name, then at least it
> >  >  should be conditionalized so that systems with ptsname() use it, only
> >  >  falling back to using the 'name' arg to openpty() for OS lacking ptsname
> >
> >
> > I'm not convinced (yet?) this will be worth it.
> 
> Glibc uses an internal PATH_MAX buffer. If the name does not fit, the
> buffer will be doubled in size:
> http://sourceware.org/cgi-bin/cvsweb.cgi/libc/login/openpty.c?rev=1.8&content-type=text/x-cvsweb-markup&cvsroot=glibc
> 
> But in practice the pty will be allocated using getpt(), which uses
> hard coded ptmx name:
> http://sourceware.org/cgi-bin/cvsweb.cgi/libc/sysdeps/unix/sysv/linux/getpt.c?rev=1.10&content-type=text/x-cvsweb-markup&cvsroot=glibc
> 
> And ptsname() is used to get the pty name, which uses either hard
> coded buffer length of _PATH_DEVPTS or _PATH_TTY:
> http://sourceware.org/cgi-bin/cvsweb.cgi/libc/sysdeps/unix/sysv/linux/ptsname.c?rev=1.15&content-type=text/x-cvsweb-markup&cvsroot=glibc
> 
> OpenBSD forces the name to be in format "/dev/ptyXX":
> http://www.openbsd.org/cgi-bin/cvsweb/src/lib/libutil/pty.c?rev=1.15&content-type=text/x-cvsweb-markup
> 
> NetBSD is similar, except also /dev/ttyXX is possible:
> http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libutil/pty.c?rev=1.29&content-type=text/x-cvsweb-markup
> 
> I still maintain that in reality, PATH_MAX should be enough.

Ok, I guess its safe enough in practice then.

Regards,
Daniel
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