Re: [PATCH] linux ttyname and ttyname_r: do not return wrong results

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

Quoting Christian Brauner (christian.brauner@canonical.com):
> If a link (say /proc/self/fd/0) pointing to a device, say /dev/pts/2, in a
> parent mount namespace is passed to ttyname, 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.
> 
> Detect this case and return ENODEV. Userspace can choose to take this as a hint
> that the fd points to a tty device but to act on the fd rather than the link.
> 
> Signed-off-by: Serge Hallyn <serge@hallyn.com>
> Signed-off-by: Christian Brauner <christian.brauner@canonical.com>

Thanks !

> ---
> Changelog: 2016-11-08
> 	- remove obsolete comment in ttyname_r.c
> 	- move is_pty() to common header file and mark as static inline
> ---
>  sysdeps/unix/sysv/linux/ttyname.c   | 17 +++++++++++++----
>  sysdeps/unix/sysv/linux/ttyname.h   | 35 +++++++++++++++++++++++++++++++++++
>  sysdeps/unix/sysv/linux/ttyname_r.c | 18 ++++++++++++++----
>  3 files changed, 62 insertions(+), 8 deletions(-)
>  create mode 100644 sysdeps/unix/sysv/linux/ttyname.h
> 
> diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
> index 7a001b4..dabed22 100644
> --- a/sysdeps/unix/sysv/linux/ttyname.c
> +++ b/sysdeps/unix/sysv/linux/ttyname.c
> @@ -25,9 +25,12 @@
>  #include <unistd.h>
>  #include <string.h>
>  #include <stdlib.h>
> +#include <sys/sysmacros.h>
>  
>  #include <_itoa.h>
>  
> +#include "ttyname.h"
> +
>  #if 0
>  /* Is this used anywhere?  It is not exported.  */
>  char *__ttyname;
> @@ -170,12 +173,18 @@ 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_ino == st.st_ino
> +	  && st1.st_dev == st.st_dev)
>  	return ttyname_buf;
> +
> +      /* If the link doesn't exist, then it points to a device in another
> +	 namespace. */
> +      if (is_pty (&st))
> +	{
> +	  __set_errno (ENODEV);
> +	  return NULL;
> +	}
>      }
>  
>    if (__xstat64 (_STAT_VER, "/dev/pts", &st1) == 0 && S_ISDIR (st1.st_mode))
> diff --git a/sysdeps/unix/sysv/linux/ttyname.h b/sysdeps/unix/sysv/linux/ttyname.h
> new file mode 100644
> index 0000000..19af6e6
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/ttyname.h
> @@ -0,0 +1,35 @@
> +/* Copyright (C) 2004-2016 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public License as
> +   published by the Free Software Foundation; either version 2.1 of the
> +   License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; see the file COPYING.LIB.  If
> +   not, see <http://www.gnu.org/licenses/>.  */
> +
> +#include <unistd.h>
> +#include <sys/sysmacros.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +
> +/* Return true if this is a UNIX98 pty device, as defined in
> +   linux/Documentation/devices.txt.  */
> +static inline 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
> +}
> +
> diff --git a/sysdeps/unix/sysv/linux/ttyname_r.c b/sysdeps/unix/sysv/linux/ttyname_r.c
> index d15bc74..542114b 100644
> --- a/sysdeps/unix/sysv/linux/ttyname_r.c
> +++ b/sysdeps/unix/sysv/linux/ttyname_r.c
> @@ -25,9 +25,12 @@
>  #include <unistd.h>
>  #include <string.h>
>  #include <stdlib.h>
> +#include <sys/sysmacros.h>
>  
>  #include <_itoa.h>
>  
> +#include "ttyname.h"
> +
>  static int getttyname_r (char *buf, size_t buflen,
>  			 dev_t mydev, ino64_t myino, int save,
>  			 int *dostat) internal_function;
> @@ -152,12 +155,19 @@ __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
> -	  && st1.st_ino == st.st_ino
> -	  && st1.st_dev == st.st_dev
>  #endif
> -	  )
> +	  && st1.st_ino == st.st_ino
> +	  && st1.st_dev == st.st_dev)
>  	return 0;
> +
> +      /* If the link doesn't exist, then it points to a device in another
> +       * namespace.
> +       */
> +      if (is_pty (&st))
> +	{
> +	  __set_errno (ENODEV);
> +	  return ENODEV;
> +	}
>      }
>  
>    /* Prepare the result buffer.  */
> -- 
> 2.9.3