diff mbox

linux ttyname and ttyname_r: return link if appropriate

Message ID 20160420185141.GA31095@ubuntumail
State New
Headers show

Commit Message

Serge E. Hallyn April 20, 2016, 6:51 p.m. UTC 
Quoting Mike Frysinger (vapier@gentoo.org):
> On 20 Apr 2016 02:10, Serge Hallyn wrote:
> > --- a/sysdeps/unix/sysv/linux/ttyname.c
> > +++ b/sysdeps/unix/sysv/linux/ttyname.c
> >
> > +   linux/Documentation/devices.txt */
> 
> should be a period at the end followed by two spaces
> 
> > +  int m = major (sb->st_rdev);
> 
> you'll need to include sys/sysmacros.h in this file since you're using
> major now.

Hm, odd - it did build here fine.  But presumably that's due to
something in my local environment, so added it.  New version below,
thanks.

> > +      /* 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 */
> 
> should be "namespace.  */" at the end ;)
> 
> > --- a/sysdeps/unix/sysv/linux/ttyname_r.c
> > +++ b/sysdeps/unix/sysv/linux/ttyname_r.c
> 
> same comments here
> -mike

Subject: 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   | 21 +++++++++++++++++++++
 sysdeps/unix/sysv/linux/ttyname_r.c | 23 +++++++++++++++++++++++
 2 files changed, 44 insertions(+)

Comments

Serge E. Hallyn July 27, 2016, 1:28 p.m. UTC | #1 
Hi,

back in april we went through some back and forth on this patch to fix a
behavior in ttyname which broke containers in some setups.  It also now
apparently breaks the package manager dnf in some setups.  The last
email appears to be this one

https://sourceware.org/ml/libc-alpha/2016-04/msg00500.html

I just checked, and the patch still applies cleanly to today's git head. If
there are no further objections could this patch be applied?

thanks,
-serge
Dmitry V. Levin July 27, 2016, 4:57 p.m. UTC | #2 
On Wed, Apr 20, 2016 at 06:51:41PM +0000, Serge Hallyn wrote:
> 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.
[...]
> --- a/sysdeps/unix/sysv/linux/ttyname.c
> +++ b/sysdeps/unix/sysv/linux/ttyname.c
[...]
> @@ -170,12 +184,19 @@ 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

__ttyname_r also needs this st_dev check.

To be on the safe side, I'd check st_ino in _STATBUF_ST_RDEV case as well.
diff mbox

Patch

diff --git a/sysdeps/unix/sysv/linux/ttyname.c b/sysdeps/unix/sysv/linux/ttyname.c
index 7a001b4..d0d8d2c 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 +184,19 @@  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 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..d5f6f05 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,
@@ -158,6 +172,15 @@  __ttyname_r (int fd, char *buf, size_t buflen)
 #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.  */