[PATCH 1/1] linux ttyname and ttyname_r: do not return wrong results

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

If a link (say /proc/self/fd/0) pointint 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.
---
 sysdeps/unix/sysv/linux/ttyname.c   | 28 ++++++++++++++++++++++++----
 sysdeps/unix/sysv/linux/ttyname_r.c | 29 +++++++++++++++++++++++++----
 2 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
index 7a001b4..798f396 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 +184,18 @@ 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_r.c b/sysdeps/unix/sysv/linux/ttyname_r.c
index d15bc74..2573729 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 +166,19 @@ __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 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))
+	{
+	  __set_errno (ENODEV);
+	  return ENODEV;
+	}
     }
 
   /* Prepare the result buffer.  */
-- 
2.7.4