tst-ttyname failure

[Florian Weimer <fweimer at redhat dot com>]

I need the two attached patches in order to get tst-ttyname to succeed 
when running on Fedora as a non-root user.

info:  entering chroot 1
info:    testcase: basic smoketest
info:      ttyname: PASS {name="/dev/pts/5", errno=0}
info:      ttyname_r: PASS {name="/dev/pts/5", ret=0, errno=0}
error: ../sysdeps/unix/sysv/linux/tst-ttyname.c:122: write (setroups, 
"deny"): Operation not permitted
info:  entering chroot 2
error: ../sysdeps/unix/sysv/linux/tst-ttyname.c:122: write (setroups, 
"deny"): Operation not permitted
error: 2 test failures

I get the same failure when running the test on 
kernel-3.10.0-768.el7.x86_64 (there I tested as root).

This is on top of master with commit 
ce003e5d4cd94c5380699b0dadeaaf825813afbe (support_become_root: Enable 
file creation in user namespaces).  The test failure was present before 
I pushed that change.

Would you please double-check that they do not break the test on 
whatever distributions you tested on and do not interfere with the test 
objective?

Thanks,
Florian

Subject: [PATCH] support_enter_mount_namespace: Unshare with mount --make-rprivate
To: libc-alpha@sourceware.org

System defaults vary, and a mere unshare (CLONE_NEWNS) (which is part of
support_become_root) is no longer sufficient.

2017-11-17  Florian Weimer  <fweimer@redhat.com>

	* support/namespace.h (support_enter_mount_namespace): Declare.
	* support/support_enter_mount_namespace.c: New file.
	* support/Makefile (libsupport-routines): Add
	support_enter_mount_namespace.

diff --git a/support/Makefile b/support/Makefile
index f7a878b950..384fecb65a 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -42,6 +42,7 @@ libsupport-routines = \
   support_capture_subprocess \
   support_capture_subprocess_check \
   support_chroot \
+  support_enter_mount_namespace \
   support_enter_network_namespace \
   support_format_address_family \
   support_format_addrinfo \
diff --git a/support/namespace.h b/support/namespace.h
index 9eddb1a0e9..b5e2d1474a 100644
--- a/support/namespace.h
+++ b/support/namespace.h
@@ -51,6 +51,11 @@ bool support_can_chroot (void);
    has sufficient privileges.  */
 bool support_enter_network_namespace (void);
 
+/* Enter a mount namespace and mark / as private (not shared).  If
+   this function returns true, mount operations in this process will
+   not affect the host system afterwards.  */
+bool support_enter_mount_namespace (void);
+
 /* Return true if support_enter_network_namespace managed to enter a
    UTS namespace.  */
 bool support_in_uts_namespace (void);
diff --git a/support/support_enter_mount_namespace.c b/support/support_enter_mount_namespace.c
new file mode 100644
index 0000000000..6140692075
--- /dev/null
+++ b/support/support_enter_mount_namespace.c
@@ -0,0 +1,45 @@
+/* Enter a mount namespace.
+   Copyright (C) 2017 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; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <support/namespace.h>
+
+#include <sched.h>
+#include <stdio.h>
+#include <sys/mount.h>
+
+bool
+support_enter_mount_namespace (void)
+{
+#ifdef CLONE_NEWNS
+  if (unshare (CLONE_NEWNS) == 0)
+    {
+      /* On some systems, / is marked as MS_SHARED, which means that
+         mounts within the namespace leak to the rest of the system,
+         which is not what we want.  */
+      if (mount ("none", "/", NULL, MS_REC | MS_PRIVATE, NULL) != 0)
+        {
+          printf ("warning: making the mount namespace private failed: %m\n");
+          return false;
+        }
+      return true;
+    }
+  else
+    printf ("warning: unshare (CLONE_NEWNS) failed: %m\n");
+#endif /* CLONE_NEWNS */
+  return false;
+}

Subject: [PATCH] tst-ttyname: Fix namespace setup for Fedora
To: libc-alpha@sourceware.org

On Fedora, the previous initialization sequence did not work and
resulted in failures like:

info:  entering chroot 1
info:    testcase: basic smoketest
info:      ttyname: PASS {name="/dev/pts/5", errno=0}
info:      ttyname_r: PASS {name="/dev/pts/5", ret=0, errno=0}
error: ../sysdeps/unix/sysv/linux/tst-ttyname.c:122: write (setroups, "deny"): Operation not permitted
info:  entering chroot 2
error: ../sysdeps/unix/sysv/linux/tst-ttyname.c:122: write (setroups, "deny"): Operation not permitted
error: 2 test failures

2017-11-17  Florian Weimer  <fweimer@redhat.com>

	* sysdeps/unix/sysv/linux/tst-ttyname.c
	(become_root_in_mount_ns): Remove.
	(do_in_chroot_1): Call support_enter_mount_namespace.
	(do_in_chroot_2): Likewise.
	(do_test): Call support_become_root early.

diff --git a/sysdeps/unix/sysv/linux/tst-ttyname.c b/sysdeps/unix/sysv/linux/tst-ttyname.c
index 32d7a65938..0fdf1a8ccb 100644
--- a/sysdeps/unix/sysv/linux/tst-ttyname.c
+++ b/sysdeps/unix/sysv/linux/tst-ttyname.c
@@ -78,65 +78,6 @@ proc_fd_readlink (const char *linkname)
   return target;
 }
 
-static void
-become_root_in_mount_ns (void)
-{
-  uid_t orig_uid = getuid ();
-  gid_t orig_gid = getgid ();
-
-  support_become_root ();
-
-  if (unshare (CLONE_NEWNS) < 0)
-    FAIL_UNSUPPORTED ("could not enter new mount namespace");
-
-  /* support_become_root might have put us in a new user namespace;
-     most filesystems (including tmpfs) don't allow file or directory
-     creation from a user namespace unless uid and gid maps are set,
-     even if we have root privileges in the namespace (failing with
-     EOVERFLOW, since the uid overflows the empty (0-length) uid map).
-
-     Also, stat always reports that uid and gid maps are empty, so we
-     have to try actually reading from them to check if they are
-     empty.  */
-  int fd;
-
-  if ((fd = open ("/proc/self/uid_map", O_RDWR, 0)) >= 0)
-    {
-      char buf;
-      if (read (fd, &buf, 1) == 0)
-	{
-	  char *str = xasprintf ("0 %ld 1\n", (long)orig_uid);
-	  if (write (fd, str, strlen (str)) < 0)
-	    FAIL_EXIT1 ("write (uid_map, \"%s\"): %m", str);
-	  free (str);
-	}
-      xclose (fd);
-    }
-
-  /* Setting the gid map has the additional complexity that we have to
-     first turn off setgroups.  */
-  if ((fd = open ("/proc/self/setgroups", O_WRONLY, 0)) >= 0)
-    {
-      const char *str = "deny";
-      if (write (fd, str, strlen (str)) < 0)
-	FAIL_EXIT1 ("write (setroups, \"%s\"): %m", str);
-      xclose (fd);
-    }
-
-  if ((fd = open ("/proc/self/gid_map", O_RDWR, 0)) >= 0)
-    {
-      char buf;
-      if (read (fd, &buf, 1) == 0)
-	{
-	  char *str = xasprintf ("0 %ld 1\n", (long)orig_gid);
-	  if (write (fd, str, strlen (str)) < 0)
-	    FAIL_EXIT1 ("write (gid_map, \"%s\"): %m", str);
-	  free (str);
-	}
-      xclose (fd);
-    }
-}
-
 /* plain ttyname runner */
 
 struct result
@@ -328,7 +269,8 @@ do_in_chroot_1 (int (*cb)(const char *, int))
     {
       xclose (master);
 
-      become_root_in_mount_ns ();
+      if (!support_enter_mount_namespace ())
+	FAIL_UNSUPPORTED ("could not enter new mount namespace");
 
       VERIFY (mount ("tmpfs", chrootdir, "tmpfs", 0, "mode=755") == 0);
       VERIFY (chdir (chrootdir) == 0);
@@ -395,7 +337,8 @@ do_in_chroot_2 (int (*cb)(const char *, int))
       xclose (pid_pipe[0]);
       xclose (exit_pipe[1]);
 
-      become_root_in_mount_ns ();
+      if (!support_enter_mount_namespace ())
+	FAIL_UNSUPPORTED ("could not enter new mount namespace");
 
       int slave = xopen (slavename, O_RDWR, 0);
       if (!doit (slave, "basic smoketest",
@@ -611,6 +554,8 @@ run_chroot_tests (const char *slavename, int slave)
 static int
 do_test (void)
 {
+  support_become_root ();
+
   int ret1 = do_in_chroot_1 (run_chroot_tests);
   if (ret1 == EXIT_UNSUPPORTED)
     return ret1;