[PATCH 1/1] linux ttyname: return link if appropriate

[Serge Hallyn <serge dot hallyn at ubuntu dot com>]

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.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
---
 sysdeps/unix/sysv/linux/ttyname.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
index 7a001b4..b0500a9 100644
--- a/sysdeps/unix/sysv/linux/ttyname.c
+++ b/sysdeps/unix/sysv/linux/ttyname.c
@@ -170,12 +170,21 @@ ttyname (int fd)
 #ifdef _STATBUF_ST_RDEV
 	  && S_ISCHR (st1.st_mode)
 	  && st1.st_rdev == st.st_rdev
+	  && st1.st_dev == st.st_dev
 #else
 	  && st1.st_ino == st.st_ino
 	  && st1.st_dev == st.st_dev
 #endif
 	  )
 	return ttyname_buf;
+      /* If the link doesn't exist, then it points to a dvice in another
+       * namespace.  We've already verified it's a tty.  Just return the
+       * link itself. */
+      if (strlen(procname) < buflen - 1) {
+         memcpy(ttyname_buf, procname, strlen(procname));
+         ttyname_buf[strlen(procname)] = '\0';
+         return ttyname_buf;
+      }
     }
 
   if (__xstat64 (_STAT_VER, "/dev/pts", &st1) == 0 && S_ISDIR (st1.st_mode))
-- 
2.7.4