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

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

Quoting Serge E. Hallyn (serge@hallyn.com):
> Quoting Mike Frysinger (vapier@gentoo.org):
> > On 05 Aug 2016 21:08, Serge E. Hallyn wrote:
> > >  #ifdef _STATBUF_ST_RDEV
> > >  	  && S_ISCHR (st1.st_mode)
> > >  	  && st1.st_rdev == st.st_rdev
> > > +	  && st1.st_dev == st.st_dev
> > > +	  && st1.st_ino == st.st_ino
> > >  #else
> > >  	  && st1.st_ino == st.st_ino
> > >  	  && st1.st_dev == st.st_dev
> > >  #endif
> > 
> > wouldn't it be better to shuffle the ifdef then ?
> > 	#ifdef _STATBUF_ST_RDEV
> > 		&& S_ISCHR (st1.st_mode)
> > 		&& st1.st_rdev == st.st_rdev
> > 	#endif
> > 		&& st1.st_ino == st.st_ino
> > 		&& st1.st_dev == st.st_dev)
> 
> That occurred to me when I looked at it again after sending,
> seems reasonable.

Is this now ready to be applied?  More peopel appear to be running into
it, https://github.com/lxc/lxc/issues/554

> Subject: [PATCH] linux ttyname and ttyname_r: 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.
> ---
>  sysdeps/unix/sysv/linux/ttyname.c   | 25 ++++++++++++++++++++++---
>  sysdeps/unix/sysv/linux/ttyname_r.c | 26 ++++++++++++++++++++++++--
>  2 files changed, 46 insertions(+), 5 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
> index 7a001b4..3065ed4 100644
> --- a/sysdeps/unix/sysv/linux/ttyname.c
> +++ b/sysdeps/unix/sysv/linux/ttyname.c
> @@ -25,6 +25,7 @@
>  #include <unistd.h>
>  #include <string.h>
>  #include <stdlib.h>
> +#include <sys/sysmacros.h>
>  
>  #include <_itoa.h>
>  
> @@ -33,6 +34,19 @@
>  char *__ttyname;
>  #endif
>  
> +/* Return true if this is a UNIX98 pty device, as defined in
> +   linux/Documentation/devices.txt.  */
> +static int
> +is_pty (struct stat64 *sb)
> +{
> +#ifdef _STATBUF_ST_RDEV
> +  int m = major (sb->st_rdev);
> +  return (136 <= m && m <= 143);
> +#else
> +  return false;
> +#endif
> +}
> +
>  static char *getttyname (const char *dev, dev_t mydev,
>  			 ino64_t myino, int save, int *dostat)
>       internal_function;
> @@ -170,12 +184,17 @@ ttyname (int fd)
>  #ifdef _STATBUF_ST_RDEV
>  	  && S_ISCHR (st1.st_mode)
>  	  && st1.st_rdev == st.st_rdev
> -#else
> -	  && st1.st_ino == st.st_ino
> -	  && st1.st_dev == st.st_dev
>  #endif
> +	  && st1.st_dev == st.st_dev
> +	  && st1.st_ino == st.st_ino
>  	  )
>  	return ttyname_buf;
> +
> +      /* 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);
>      }
>  
>    if (__xstat64 (_STAT_VER, "/dev/pts", &st1) == 0 && S_ISDIR (st1.st_mode))
> diff --git a/sysdeps/unix/sysv/linux/ttyname_r.c b/sysdeps/unix/sysv/linux/ttyname_r.c
> index d15bc74..97527c0 100644
> --- a/sysdeps/unix/sysv/linux/ttyname_r.c
> +++ b/sysdeps/unix/sysv/linux/ttyname_r.c
> @@ -25,6 +25,7 @@
>  #include <unistd.h>
>  #include <string.h>
>  #include <stdlib.h>
> +#include <sys/sysmacros.h>
>  
>  #include <_itoa.h>
>  
> @@ -32,6 +33,19 @@ static int getttyname_r (char *buf, size_t buflen,
>  			 dev_t mydev, ino64_t myino, int save,
>  			 int *dostat) internal_function;
>  
> +/* Return true if this is a UNIX98 pty device, as defined in
> +   linux/Documentation/devices.txt.  */
> +static int
> +is_pty (struct stat64 *sb)
> +{
> +#ifdef _STATBUF_ST_RDEV
> +  int m = major (sb->st_rdev);
> +  return (136 <= m && m <= 143);
> +#else
> +  return false;
> +#endif
> +}
> +
>  static int
>  internal_function attribute_compat_text_section
>  getttyname_r (char *buf, size_t buflen, dev_t mydev, ino64_t myino,
> @@ -152,12 +166,20 @@ __ttyname_r (int fd, char *buf, size_t buflen)
>  #ifdef _STATBUF_ST_RDEV
>  	  && S_ISCHR (st1.st_mode)
>  	  && st1.st_rdev == st.st_rdev
> -#else
> +#endif
>  	  && st1.st_ino == st.st_ino
>  	  && st1.st_dev == st.st_dev
> -#endif
>  	  )
>  	return 0;
> +
> +      /* 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;
> +	}
>      }
>  
>    /* Prepare the result buffer.  */
> -- 
> 2.7.4