diff --git a/ChangeLog b/ChangeLog
index 9ea727499c..f677ef4d72 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2017-11-07  Luke Shumaker  <lukeshu@parabola.nu>
 
+	[BZ #22145]
+	* sysdeps/unix/sysv/linux/tst-ttyname.c: New file.
+	* sysdeps/unix/sysv/linux/Makefile: Add tst-ttyname to tests.
+
 	[BZ #22145]
 	* sysdeps/unix/sysv/linux/ttyname.c (ttyname):
 	Defer is_pty check until end of the function.
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index bf76b8773d..c6675b3aa5 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -43,7 +43,8 @@ sysdep_headers += sys/mount.h sys/acct.h sys/sysctl.h \
 		  bits/siginfo-arch.h bits/siginfo-consts-arch.h
 
 tests += tst-clone tst-clone2 tst-clone3 tst-fanotify tst-personality \
-	 tst-quota tst-sync_file_range test-errno-linux tst-sysconf-iov_max
+	 tst-quota tst-sync_file_range tst-sysconf-iov_max tst-ttyname \
+	 test-errno-linux
 
 # Generate the list of SYS_* macros for the system calls (__NR_*
 # macros).  The file syscall-names.list contains all possible system
diff --git a/sysdeps/unix/sysv/linux/tst-ttyname.c b/sysdeps/unix/sysv/linux/tst-ttyname.c
new file mode 100644
index 0000000000..a5a4bb9689
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-ttyname.c
@@ -0,0 +1,625 @@
+/* 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; see the file COPYING.LIB.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <sched.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/prctl.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/test-driver.h>
+#include <support/xunistd.h>
+
+/* generic utilities */
+
+#define VERIFY(expr)                                                    \
+  do {                                                                  \
+    if (!(expr))                                                        \
+      {                                                                 \
+        printf ("error: %s:%d: %s: %m\n",                               \
+                __FILE__, __LINE__, #expr);                             \
+        exit (1);                                                       \
+      }                                                                 \
+  } while (0)
+
+static void
+xtouch (const char *path, mode_t mode)
+{
+  xclose (xopen (path, O_WRONLY|O_CREAT|O_NOCTTY, mode));
+}
+
+static size_t
+trim_prefix (char *str, size_t str_len, const char *prefix)
+{
+  size_t prefix_len = strlen (prefix);
+  if (str_len > prefix_len && memcmp (str, prefix, prefix_len) == 0)
+    {
+      memmove (str, str + prefix_len, str_len - prefix_len);
+      return str_len - prefix_len;
+    }
+  return str_len;
+}
+
+/* returns a pointer to static storage */
+static char *
+xreadlink (const char *linkname)
+{
+  static char target[PATH_MAX+1];
+  ssize_t target_len = readlink (linkname, target, PATH_MAX);
+  VERIFY (target_len > 0);
+  target_len = trim_prefix (target, target_len, "(unreachable)");
+  target[target_len] = '\0';
+  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
+{
+  const char *name;
+  int err;
+};
+
+/* strings in result structure are in static storage */
+static struct result
+run_ttyname (int fd)
+{
+  struct result ret;
+  errno = 0;
+  ret.name = ttyname (fd);
+  ret.err = errno;
+  return ret;
+}
+
+static bool
+eq_ttyname (struct result actual, struct result expected)
+{
+  char *actual_name, *expected_name;
+
+  if ((actual.err == expected.err) &&
+      (!actual.name == !expected.name) &&
+      (actual.name ? strcmp (actual.name, expected.name) == 0 : true))
+    {
+      if (expected.name)
+        expected_name = xasprintf ("\"%s\"", expected.name);
+      else
+	expected_name = xstrdup ("NULL");
+
+      printf ("info:      ttyname: PASS {name=%s, errno=%d}\n",
+	      expected_name, expected.err);
+
+      free (expected_name);
+      return true;
+    }
+
+  if (actual.name)
+    actual_name = xasprintf ("\"%s\"", actual.name);
+  else
+    actual_name = xstrdup ("NULL");
+
+  if (expected.name)
+    expected_name = xasprintf ("\"%s\"", expected.name);
+  else
+    expected_name = xstrdup ("NULL");
+
+  printf ("error:     ttyname: actual {name=%s, errno=%d} != expected {name=%s, errno=%d}\n",
+	  actual_name, actual.err,
+	  expected_name, expected.err);
+
+  free (actual_name);
+  free (expected_name);
+  return false;
+}
+
+/* ttyname_r runner */
+
+struct result_r
+{
+  const char *name;
+  int ret;
+  int err;
+};
+
+/* strings in result structure are in static storage */
+static struct result_r
+run_ttyname_r (int fd)
+{
+  static char buf[TTY_NAME_MAX];
+
+  struct result_r ret;
+  errno = 0;
+  ret.ret = ttyname_r (fd, buf, TTY_NAME_MAX);
+  ret.err = errno;
+  if (ret.ret == 0)
+    ret.name = buf;
+  else
+    ret.name = NULL;
+  return ret;
+}
+
+static bool
+eq_ttyname_r (struct result_r actual, struct result_r expected)
+{
+  char *actual_name, *expected_name;
+
+  if ((actual.err == expected.err) &&
+      (actual.ret == expected.ret) &&
+      (!actual.name == !expected.name) &&
+      (actual.name ? strcmp (actual.name, expected.name) == 0 : true))
+    {
+      if (expected.name)
+        expected_name = xasprintf ("\"%s\"", expected.name);
+      else
+        expected_name = xstrdup ("NULL");
+
+      printf ("info:      ttyname_r: PASS {name=%s, ret=%d, errno=%d}\n",
+              expected_name, expected.ret, expected.err);
+
+      free (expected_name);
+      return true;
+    }
+
+  if (actual.name)
+    actual_name = xasprintf ("\"%s\"", actual.name);
+  else
+    actual_name = xstrdup ("NULL");
+
+  if (expected.name)
+    expected_name = xasprintf ("\"%s\"", expected.name);
+  else
+    expected_name = xstrdup ("NULL");
+
+  printf ("error:     ttyname_r: actual {name=%s, ret=%d, errno=%d} != expected {name=%s, ret=%d, errno=%d}\n",
+	  actual_name, actual.ret, actual.err,
+	  expected_name, expected.ret, expected.err);
+
+  free (actual_name);
+  free (expected_name);
+  return false;
+}
+
+/* combined runner */
+
+static bool
+doit (int fd, const char *testname, struct result_r expected_r)
+{
+  struct result expected = {.name=expected_r.name, .err=expected_r.ret};
+  bool ret = true;
+
+  printf ("info:    testcase: %s\n", testname);
+
+  if (!eq_ttyname (run_ttyname (fd), expected))
+    ret = false;
+  if (!eq_ttyname_r (run_ttyname_r (fd), expected_r))
+    ret = false;
+
+  if (!ret)
+    support_record_failure ();
+
+  return ret;
+}
+
+/* chroot setup */
+
+static char *chrootdir;
+
+static void
+prepare (int argc, char **argv)
+{
+  chrootdir = xasprintf ("%s/tst-ttyname-XXXXXX", test_dir);
+  if (mkdtemp (chrootdir) == NULL)
+    FAIL_EXIT1 ("mkdtemp (\"%s\"): %m", chrootdir);
+  add_temp_file (chrootdir);
+}
+#define PREPARE prepare
+
+/* These chroot setup functions put the TTY at at "/console" (where it
+   won't be found by ttyname), and create "/dev/console" as an
+   ordinary file.  This way, it's easier to write test-cases that
+   expect ttyname to fail; test-cases that expect it to succeed need
+   to explicitly remount it at "/dev/console".  */
+
+static int
+do_in_chroot_1 (int (*cb)(const char *, int))
+{
+  printf ("info:  entering chroot 1\n");
+
+  /* Open the PTS that we'll be testing on.  */
+  int master;
+  char *slavename;
+  VERIFY ((master = posix_openpt (O_RDWR|O_NOCTTY|O_NONBLOCK)) >= 0);
+  VERIFY ((slavename = ptsname (master)));
+  VERIFY (unlockpt (master) == 0);
+  if (strncmp (slavename, "/dev/pts/", 9) != 0)
+    FAIL_UNSUPPORTED ("slave pseudo-terminal is not under /dev/pts/: %s",
+                      slavename);
+  int slave = xopen (slavename, O_RDWR, 0);
+  if (!doit (slave, "basic smoketest",
+             (struct result_r){.name=slavename, .ret=0, .err=0}))
+    return 1;
+
+  pid_t pid = xfork ();
+  if (pid == 0)
+    {
+      xclose (master);
+
+      become_root_in_mount_ns ();
+
+      VERIFY (mount ("tmpfs", chrootdir, "tmpfs", 0, "mode=755") == 0);
+      VERIFY (chdir (chrootdir) == 0);
+
+      xmkdir ("proc", 0755);
+      xmkdir ("dev", 0755);
+      xmkdir ("dev/pts", 0755);
+
+      VERIFY (mount ("/proc", "proc", NULL, MS_BIND|MS_REC, NULL) == 0);
+      VERIFY (mount ("devpts", "dev/pts", "devpts",
+                     MS_NOSUID|MS_NOEXEC,
+                     "newinstance,ptmxmode=0666,mode=620") == 0);
+      VERIFY (symlink ("pts/ptmx", "dev/ptmx") == 0);
+
+      xtouch ("console", 0);
+      xtouch ("dev/console", 0);
+      VERIFY (mount (slavename, "console", NULL, MS_BIND, NULL) == 0);
+
+      xchroot (".");
+
+      char *linkname = xasprintf ("/proc/self/fd/%d", slave);
+      char *target = xreadlink (linkname);
+      VERIFY (strcmp (target, slavename) == 0);
+      free (linkname);
+
+      _exit (cb (slavename, slave));
+    }
+  int status;
+  xwaitpid (pid, &status, 0);
+  VERIFY (WIFEXITED (status));
+  xclose (master);
+  xclose (slave);
+  return WEXITSTATUS (status);
+}
+
+static int
+do_in_chroot_2 (int (*cb)(const char *, int))
+{
+  printf ("info:  entering chroot 2\n");
+
+  int pid_pipe[2];
+  xpipe (pid_pipe);
+  int exit_pipe[2];
+  xpipe (exit_pipe);
+
+  /* Open the PTS that we'll be testing on.  */
+  int master;
+  char *slavename;
+  VERIFY ((master = posix_openpt (O_RDWR|O_NOCTTY|O_NONBLOCK)) >= 0);
+  VERIFY ((slavename = ptsname (master)));
+  VERIFY (unlockpt (master) == 0);
+  if (strncmp (slavename, "/dev/pts/", 9) != 0)
+    FAIL_UNSUPPORTED ("slave pseudo-terminal is not under /dev/pts/: %s",
+                      slavename);
+  /* wait until in a new mount ns to open the slave */
+
+  /* enable `wait`ing on grandchildren */
+  VERIFY (prctl (PR_SET_CHILD_SUBREAPER, 1) == 0);
+
+  pid_t pid = xfork (); /* outer child */
+  if (pid == 0)
+    {
+      xclose (master);
+      xclose (pid_pipe[0]);
+      xclose (exit_pipe[1]);
+
+      become_root_in_mount_ns ();
+
+      int slave = xopen (slavename, O_RDWR, 0);
+      if (!doit (slave, "basic smoketest",
+                 (struct result_r){.name=slavename, .ret=0, .err=0}))
+        _exit (1);
+
+      VERIFY (mount ("tmpfs", chrootdir, "tmpfs", 0, "mode=755") == 0);
+      VERIFY (chdir (chrootdir) == 0);
+
+      xmkdir ("proc", 0755);
+      xmkdir ("dev", 0755);
+      xmkdir ("dev/pts", 0755);
+
+      VERIFY (mount ("devpts", "dev/pts", "devpts",
+                     MS_NOSUID|MS_NOEXEC,
+                     "newinstance,ptmxmode=0666,mode=620") == 0);
+      VERIFY (symlink ("pts/ptmx", "dev/ptmx") == 0);
+
+      xtouch ("console", 0);
+      xtouch ("dev/console", 0);
+      VERIFY (mount (slavename, "console", NULL, MS_BIND, NULL) == 0);
+
+      xchroot (".");
+
+      if (unshare (CLONE_NEWNS | CLONE_NEWPID) < 0)
+        FAIL_UNSUPPORTED ("could not enter new PID namespace");
+      pid = xfork (); /* inner child */
+      if (pid == 0)
+        {
+          xclose (pid_pipe[1]);
+
+          /* wait until the outer child has exited */
+          char c;
+          VERIFY (read (exit_pipe[0], &c, 1) == 0);
+          xclose (exit_pipe[0]);
+
+          VERIFY (mount ("proc", "/proc", "proc",
+                         MS_NOSUID|MS_NOEXEC|MS_NODEV, NULL) == 0);
+
+          char *linkname = xasprintf ("/proc/self/fd/%d", slave);
+          char *target = xreadlink (linkname);
+          VERIFY (strcmp (target, strrchr (slavename, '/')) == 0);
+          free (linkname);
+
+          _exit (cb (slavename, slave));
+        }
+      xwrite (pid_pipe[1], &pid, sizeof pid);
+      _exit (0);
+    }
+  xclose (pid_pipe[1]);
+  xclose (exit_pipe[0]);
+  xclose (exit_pipe[1]);
+
+  /* wait for the outer child */
+  int status;
+  xwaitpid (pid, &status, 0);
+  VERIFY (WIFEXITED (status));
+  int ret = WEXITSTATUS (status);
+  if (ret != 0)
+    return ret;
+
+  /* set 'pid' to the inner child */
+  VERIFY (read (pid_pipe[0], &pid, sizeof pid) == sizeof pid);
+  xclose (pid_pipe[0]);
+
+  /* wait for the inner child */
+  xwaitpid (pid, &status, 0);
+  VERIFY (WIFEXITED (status));
+  xclose (master);
+  return WEXITSTATUS (status);
+}
+
+/* main test */
+
+static int
+run_chroot_tests (const char *slavename, int slave)
+{
+  struct stat st;
+  bool ok = true;
+
+  /* There are 3 groups of tests here.  The first group fairly
+     generically does things known to mess up ttyname, and verifies
+     that ttyname copes correctly.  The remaining groups are
+     increasingly convoluted, as we target specific parts of ttyname
+     to try to confuse.  */
+
+  /* Basic tests that it doesn't get confused by multiple devpts
+     instances.  */
+  {
+    VERIFY (stat (slavename, &st) < 0); /* sanity check */
+    if (!doit (slave, "no conflict, no match",
+               (struct result_r){.name=NULL, .ret=ENODEV, .err=ENODEV}))
+      ok = false;
+    VERIFY (mount ("/console", "/dev/console", NULL, MS_BIND, NULL) == 0);
+    if (!doit (slave, "no conflict, console",
+               (struct result_r){.name="/dev/console", .ret=0, .err=0}))
+      ok = false;
+    VERIFY (umount ("/dev/console") == 0);
+
+    /* keep creating PTYs until we we get a name collision */
+    while (stat (slavename, &st) < 0)
+      posix_openpt (O_RDWR|O_NOCTTY|O_NONBLOCK);
+    VERIFY (stat (slavename, &st) == 0);
+
+    if (!doit (slave, "conflict, no match",
+               (struct result_r){.name=NULL, .ret=ENODEV, .err=ENODEV}))
+      ok = false;
+    VERIFY (mount ("/console", "/dev/console", NULL, MS_BIND, NULL) == 0);
+    if (!doit (slave, "conflict, console",
+               (struct result_r){.name="/dev/console", .ret=0, .err=0}))
+      ok = false;
+    VERIFY (umount ("/dev/console") == 0);
+  }
+
+  /* The first tests kinda assumed that they hit certain code-paths
+     based on assuming that the readlink target is 'slavename', but
+     that's not quite always true.  They're still a good preliminary
+     sanity check, so keep them, but let's add tests that make sure
+     that those code-paths are hit by doing a readlink ourself.  */
+  {
+    char *linkname = xasprintf ("/proc/self/fd/%d", slave);
+    char *target = xreadlink (linkname);
+    free (linkname);
+    /* Depeding on how we set up the chroot, the kernel may or may not
+       trim the leading path to the target (it may give us "/6",
+       instead of "/dev/pts/6").  We test it both ways (do_in_chroot_1
+       and do_in_chroot_2).  This test group relies on the target
+       existing, so guarantee that it does exist by creating it if
+       necessary.  */
+    if (stat (target, &st) < 0)
+      {
+        VERIFY (errno == ENOENT);
+        xtouch (target, 0);
+      }
+
+    VERIFY (mount ("/console", "/dev/console", NULL, MS_BIND, NULL) == 0);
+    VERIFY (mount ("/console", target, NULL, MS_BIND, NULL) == 0);
+    if (!doit (slave, "with readlink target",
+               (struct result_r){.name=target, .ret=0, .err=0}))
+      ok = false;
+    VERIFY (umount (target) == 0);
+    VERIFY (umount ("/dev/console") == 0);
+
+    VERIFY (mount ("/console", "/dev/console", NULL, MS_BIND, NULL) == 0);
+    VERIFY (mount (slavename, target, NULL, MS_BIND, NULL) == 0);
+    if (!doit (slave, "with readlink trap; fallback",
+               (struct result_r){.name="/dev/console", .ret=0, .err=0}))
+      ok = false;
+    VERIFY (umount (target) == 0);
+    VERIFY (umount ("/dev/console") == 0);
+
+    VERIFY (mount (slavename, target, NULL, MS_BIND, NULL) == 0);
+    if (!doit (slave, "with readlink trap; no fallback",
+               (struct result_r){.name=NULL, .ret=ENODEV, .err=ENODEV}))
+      ok = false;
+    VERIFY (umount (target) == 0);
+  }
+
+  /* This test makes sure that everything still works OK if readdir
+     finds a pseudo-match before and/or after the actual match.  Now,
+     to do that, we need to control that readdir finds the
+     pseudo-matches before and after the actual match; and there's no
+     good way to control that order in absence of whitebox testing.
+     So, just create 3 files, then use opendir/readdir to see what
+     order they are in, and assign meaning based on that order, not by
+     name; assigning the first to be a pseudo-match, the second to be
+     the actual match, and the third to be a pseudo-match.  This
+     assumes that (on tmpfs) ordering within the directory is stable
+     in the absence of modification, which seems reasonably safe.  */
+  {
+    /* since we're testing the fallback search, disable the readlink
+       happy-path */
+    VERIFY (umount2 ("/proc", MNT_DETACH) == 0);
+
+    xtouch ("/dev/console1", 0);
+    xtouch ("/dev/console2", 0);
+    xtouch ("/dev/console3", 0);
+
+    char *c[3];
+    int ci = 0;
+    DIR *dirstream = opendir ("/dev");
+    VERIFY (dirstream != NULL);
+    struct dirent *d;
+    while ((d = readdir (dirstream)) != NULL && ci < 3)
+      {
+        if (strcmp (d->d_name, "console1") &&
+            strcmp (d->d_name, "console2") &&
+            strcmp (d->d_name, "console3") )
+          continue;
+        c[ci++] = xasprintf ("/dev/%s", d->d_name);
+      }
+    VERIFY (ci == 3);
+    VERIFY (closedir (dirstream) == 0);
+
+    VERIFY (mount (slavename, c[0], NULL, MS_BIND, NULL) == 0);
+    VERIFY (mount ("/console", c[1], NULL, MS_BIND, NULL) == 0);
+    VERIFY (mount (slavename, c[2], NULL, MS_BIND, NULL) == 0);
+    VERIFY (umount2 ("/dev/pts", MNT_DETACH) == 0);
+    if (!doit (slave, "with search-path trap",
+               (struct result_r){.name=c[1], .ret=0, .err=0}))
+      ok = false;
+    for (int i = 0; i < 3; i++)
+      {
+        VERIFY (umount (c[i]) == 0);
+        VERIFY (unlink (c[i]) == 0);
+        free (c[i]);
+      }
+  }
+
+  return ok ? 0 : 1;
+}
+
+static int
+do_test (void)
+{
+  int ret1 = do_in_chroot_1 (run_chroot_tests);
+  if (ret1 == EXIT_UNSUPPORTED)
+    return ret1;
+
+  int ret2 = do_in_chroot_2 (run_chroot_tests);
+  if (ret2 == EXIT_UNSUPPORTED)
+    return ret2;
+
+  return  ret1 | ret2;
+}
+
+#include <support/test-driver.c>
