[PATCH v3] linux ttyname and ttyname_r: do not return wrong results

[PATCH v3] linux ttyname and ttyname_r: do not return wrong results

[Christian Brauner]

Hi,

I've taken over this patch from Serge who has been informed and is CCed on this
thread. There are no significant functional changes. As requested the following
this have been changed:

- remove obsolete comment in ttyname_r.c
- move is_pty() to common header file and mark as static inline

I hope this covers everything. :)

Christian

Christian Brauner (1):
  linux ttyname and ttyname_r: do not return wrong results

 ChangeLog                           |  8 ++++++++
 sysdeps/unix/sysv/linux/ttyname.c   | 16 ++++++++++++----
 sysdeps/unix/sysv/linux/ttyname.h   | 35 +++++++++++++++++++++++++++++++++++
 sysdeps/unix/sysv/linux/ttyname_r.c | 17 +++++++++++++----
 4 files changed, 68 insertions(+), 8 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/ttyname.h

-- 
2.9.3

[PATCH v3] linux ttyname and ttyname_r: do not return wrong results

[Christian Brauner]

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@ubuntu.com>
---
Changelog: 2016-11-08
	- remove obsolete comment in ttyname_r.c
	- move is_pty() to common header file and mark as static inline
Changelog: 2016-11-22
	- remove unneeded sys/symacros.h header
Changelog: 2016-11-24
	- add Changelog entry
---
 ChangeLog                           |  8 ++++++++
 sysdeps/unix/sysv/linux/ttyname.c   | 16 ++++++++++++----
 sysdeps/unix/sysv/linux/ttyname.h   | 35 +++++++++++++++++++++++++++++++++++
 sysdeps/unix/sysv/linux/ttyname_r.c | 17 +++++++++++++----
 4 files changed, 68 insertions(+), 8 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/ttyname.h

diff --git a/ChangeLog b/ChangeLog
index b6fc831..c236992 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2016-11-23  Christian Brauner  <christian.brauner@ubuntu.com>
+
+	* sysdeps/unix/sysv/linux/ttyname.c: do not return wrong results when
+	detecting tty devices residing in a different namespace
+	* sysdeps/unix/sysv/linux/ttyname_r.c: do not return wrong results when
+	detecting tty devices residing in a different namespace
+	* sysdeps/unix/sysv/linux/ttyname.h: New file
+
 2016-11-23  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #20859]
diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
index 7a001b4..0941e2c 100644
--- a/sysdeps/unix/sysv/linux/ttyname.c
+++ b/sysdeps/unix/sysv/linux/ttyname.c
@@ -28,6 +28,8 @@
 
 #include <_itoa.h>
 
+#include "ttyname.h"
+
 #if 0
 /* Is this used anywhere?  It is not exported.  */
 char *__ttyname;
@@ -170,12 +172,18 @@ 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..a1aa314
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/ttyname.h
@@ -0,0 +1,35 @@
+/* Copyright (C) 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..8b3fe53 100644
--- a/sysdeps/unix/sysv/linux/ttyname_r.c
+++ b/sysdeps/unix/sysv/linux/ttyname_r.c
@@ -28,6 +28,8 @@
 
 #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 +154,19 @@ __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

Re: [PATCH v3] linux ttyname and ttyname_r: do not return wrong results

[Dmitry V. Levin]

[-- Attachment #1: Type: text/plain, Size: 2537 bytes --]

On Thu, Nov 24, 2016 at 02:32:36AM +0100, Christian Brauner wrote:
> 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@ubuntu.com>
> ---
> Changelog: 2016-11-08
> 	- remove obsolete comment in ttyname_r.c
> 	- move is_pty() to common header file and mark as static inline
> Changelog: 2016-11-22
> 	- remove unneeded sys/symacros.h header
> Changelog: 2016-11-24
> 	- add Changelog entry
> ---
>  ChangeLog                           |  8 ++++++++
>  sysdeps/unix/sysv/linux/ttyname.c   | 16 ++++++++++++----
>  sysdeps/unix/sysv/linux/ttyname.h   | 35 +++++++++++++++++++++++++++++++++++
>  sysdeps/unix/sysv/linux/ttyname_r.c | 17 +++++++++++++----
>  4 files changed, 68 insertions(+), 8 deletions(-)
>  create mode 100644 sysdeps/unix/sysv/linux/ttyname.h
> 
> diff --git a/ChangeLog b/ChangeLog
> index b6fc831..c236992 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -1,3 +1,11 @@
> +2016-11-23  Christian Brauner  <christian.brauner@ubuntu.com>
> +
> +	* sysdeps/unix/sysv/linux/ttyname.c: do not return wrong results when
> +	detecting tty devices residing in a different namespace
> +	* sysdeps/unix/sysv/linux/ttyname_r.c: do not return wrong results when
> +	detecting tty devices residing in a different namespace
> +	* sysdeps/unix/sysv/linux/ttyname.h: New file

This doesn't quite follow the style guidelines.  A properly formatted
ChangeLog for this change would look like this:

2016-11-24  Christian Brauner  <christian.brauner@ubuntu.com>

	* sysdeps/unix/sysv/linux/ttyname.h: New file.
	* sysdeps/unix/sysv/linux/ttyname.c: Include "ttyname.h".
	(ttyname) [!_STATBUF_ST_RDEV]: Make code unconditional.
	Call is_pty when the link does not exist or does not match, fail
	with ENODEV when it returns true.
	* sysdeps/unix/sysv/linux/ttyname_r.c: Include "ttyname.h".
	(__ttyname_r) [!_STATBUF_ST_RDEV]: Make code unconditional.
	Call is_pty when the link does not exist or does not match, fail
	with ENODEV when it returns true.


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