diff mbox series

[v4,36/37] nptl: Move setxid broadcast implementation into libc

Message ID 356b91e0ae8ec0f4217ac255de0550d767752e19.1618564630.git.fweimer@redhat.com
State Committed
Commit 486010a3c8cb59df19995eac964ef51e627287a4
Headers show
Series libpthread: Remove NPTL forwarders | expand

Commit Message

Florian Weimer April 16, 2021, 9:24 a.m. UTC
The signal handler is exported as __nptl_setxid_sighandler, so
that the libpthread initialization code can install it.  This
is sufficient for now because it is guarantueed to happen before
the first pthread_create call.
---
 nptl/Makefile                              |   1 +
 nptl/Versions                              |   1 +
 nptl/allocatestack.c                       | 209 ---------------
 nptl/nptl-init.c                           |  49 +---
 nptl/nptl_setxid.c                         | 279 +++++++++++++++++++++
 nptl/pthreadP.h                            |   4 +-
 sysdeps/nptl/pthread-functions.h           |   1 -
 sysdeps/nptl/setxid.h                      |  26 +-
 sysdeps/unix/sysv/linux/internal-signals.h |   4 -
 9 files changed, 287 insertions(+), 287 deletions(-)
 create mode 100644 nptl/nptl_setxid.c
diff mbox series

Patch

diff --git a/nptl/Makefile b/nptl/Makefile
index 0d72cf8250..eb4c37854f 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -47,6 +47,7 @@  routines = \
   lowlevellock \
   nptl_deallocate_tsd \
   nptl_nthreads \
+  nptl_setxid \
   old_pthread_cond_broadcast \
   old_pthread_cond_destroy \
   old_pthread_cond_init \
diff --git a/nptl/Versions b/nptl/Versions
index 2c2c5c2078..bb9f5e4ca7 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -147,6 +147,7 @@  libc {
     __mutex_aconf;
     __nptl_deallocate_tsd;
     __nptl_nthreads;
+    __nptl_setxid_sighandler;
     __pthread_attr_copy;
     __pthread_attr_destroy;
     __pthread_attr_init;
diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 00fddbd409..f1270c3109 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -953,215 +953,6 @@  __reclaim_stacks (void)
 }
 
 
-static void
-setxid_mark_thread (struct xid_command *cmdp, struct pthread *t)
-{
-  int ch;
-
-  /* Wait until this thread is cloned.  */
-  if (t->setxid_futex == -1
-      && ! atomic_compare_and_exchange_bool_acq (&t->setxid_futex, -2, -1))
-    do
-      futex_wait_simple (&t->setxid_futex, -2, FUTEX_PRIVATE);
-    while (t->setxid_futex == -2);
-
-  /* Don't let the thread exit before the setxid handler runs.  */
-  t->setxid_futex = 0;
-
-  do
-    {
-      ch = t->cancelhandling;
-
-      /* If the thread is exiting right now, ignore it.  */
-      if ((ch & EXITING_BITMASK) != 0)
-	{
-	  /* Release the futex if there is no other setxid in
-	     progress.  */
-	  if ((ch & SETXID_BITMASK) == 0)
-	    {
-	      t->setxid_futex = 1;
-	      futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
-	    }
-	  return;
-	}
-    }
-  while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
-					       ch | SETXID_BITMASK, ch));
-}
-
-
-static void
-setxid_unmark_thread (struct xid_command *cmdp, struct pthread *t)
-{
-  int ch;
-
-  do
-    {
-      ch = t->cancelhandling;
-      if ((ch & SETXID_BITMASK) == 0)
-	return;
-    }
-  while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
-					       ch & ~SETXID_BITMASK, ch));
-
-  /* Release the futex just in case.  */
-  t->setxid_futex = 1;
-  futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
-}
-
-
-static int
-setxid_signal_thread (struct xid_command *cmdp, struct pthread *t)
-{
-  if ((t->cancelhandling & SETXID_BITMASK) == 0)
-    return 0;
-
-  int val;
-  pid_t pid = __getpid ();
-  val = INTERNAL_SYSCALL_CALL (tgkill, pid, t->tid, SIGSETXID);
-
-  /* If this failed, it must have had not started yet or else exited.  */
-  if (!INTERNAL_SYSCALL_ERROR_P (val))
-    {
-      atomic_increment (&cmdp->cntr);
-      return 1;
-    }
-  else
-    return 0;
-}
-
-/* Check for consistency across set*id system call results.  The abort
-   should not happen as long as all privileges changes happen through
-   the glibc wrappers.  ERROR must be 0 (no error) or an errno
-   code.  */
-void
-attribute_hidden
-__nptl_setxid_error (struct xid_command *cmdp, int error)
-{
-  do
-    {
-      int olderror = cmdp->error;
-      if (olderror == error)
-	break;
-      if (olderror != -1)
-	{
-	  /* Mismatch between current and previous results.  Save the
-	     error value to memory so that is not clobbered by the
-	     abort function and preserved in coredumps.  */
-	  volatile int xid_err __attribute__((unused)) = error;
-	  abort ();
-	}
-    }
-  while (atomic_compare_and_exchange_bool_acq (&cmdp->error, error, -1));
-}
-
-int
-attribute_hidden
-__nptl_setxid (struct xid_command *cmdp)
-{
-  int signalled;
-  int result;
-  lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
-
-  __xidcmd = cmdp;
-  cmdp->cntr = 0;
-  cmdp->error = -1;
-
-  struct pthread *self = THREAD_SELF;
-
-  /* Iterate over the list with system-allocated threads first.  */
-  list_t *runp;
-  list_for_each (runp, &GL (dl_stack_used))
-    {
-      struct pthread *t = list_entry (runp, struct pthread, list);
-      if (t == self)
-	continue;
-
-      setxid_mark_thread (cmdp, t);
-    }
-
-  /* Now the list with threads using user-allocated stacks.  */
-  list_for_each (runp, &GL (dl_stack_user))
-    {
-      struct pthread *t = list_entry (runp, struct pthread, list);
-      if (t == self)
-	continue;
-
-      setxid_mark_thread (cmdp, t);
-    }
-
-  /* Iterate until we don't succeed in signalling anyone.  That means
-     we have gotten all running threads, and their children will be
-     automatically correct once started.  */
-  do
-    {
-      signalled = 0;
-
-      list_for_each (runp, &GL (dl_stack_used))
-	{
-	  struct pthread *t = list_entry (runp, struct pthread, list);
-	  if (t == self)
-	    continue;
-
-	  signalled += setxid_signal_thread (cmdp, t);
-	}
-
-      list_for_each (runp, &GL (dl_stack_user))
-	{
-	  struct pthread *t = list_entry (runp, struct pthread, list);
-	  if (t == self)
-	    continue;
-
-	  signalled += setxid_signal_thread (cmdp, t);
-	}
-
-      int cur = cmdp->cntr;
-      while (cur != 0)
-	{
-	  futex_wait_simple ((unsigned int *) &cmdp->cntr, cur,
-			     FUTEX_PRIVATE);
-	  cur = cmdp->cntr;
-	}
-    }
-  while (signalled != 0);
-
-  /* Clean up flags, so that no thread blocks during exit waiting
-     for a signal which will never come.  */
-  list_for_each (runp, &GL (dl_stack_used))
-    {
-      struct pthread *t = list_entry (runp, struct pthread, list);
-      if (t == self)
-	continue;
-
-      setxid_unmark_thread (cmdp, t);
-    }
-
-  list_for_each (runp, &GL (dl_stack_user))
-    {
-      struct pthread *t = list_entry (runp, struct pthread, list);
-      if (t == self)
-	continue;
-
-      setxid_unmark_thread (cmdp, t);
-    }
-
-  /* This must be last, otherwise the current thread might not have
-     permissions to send SIGSETXID syscall to the other threads.  */
-  result = INTERNAL_SYSCALL_NCS (cmdp->syscall_no, 3,
-				 cmdp->id[0], cmdp->id[1], cmdp->id[2]);
-  int error = 0;
-  if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result)))
-    {
-      error = INTERNAL_SYSCALL_ERRNO (result);
-      __set_errno (error);
-      result = -1;
-    }
-  __nptl_setxid_error (cmdp, error);
-
-  lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
-  return result;
-}
-
 static inline void __attribute__((always_inline))
 init_one_static_tls (struct pthread *curp, struct link_map *map)
 {
diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index 48eb2e5118..28e1aebe72 100644
--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -52,7 +52,6 @@  static const char nptl_version[] __attribute_used__ = VERSION;
 #ifdef SHARED
 static const struct pthread_functions pthread_functions =
   {
-    .ptr__nptl_setxid = __nptl_setxid,
   };
 # define ptr_pthread_functions &pthread_functions
 #else
@@ -106,52 +105,6 @@  sigcancel_handler (int sig, siginfo_t *si, void *ctx)
 }
 
 
-struct xid_command *__xidcmd attribute_hidden;
-
-/* We use the SIGSETXID signal in the setuid, setgid, etc. implementations to
-   tell each thread to call the respective setxid syscall on itself.  This is
-   the handler.  */
-static void
-sighandler_setxid (int sig, siginfo_t *si, void *ctx)
-{
-  int result;
-
-  /* Safety check.  It would be possible to call this function for
-     other signals and send a signal from another process.  This is not
-     correct and might even be a security problem.  Try to catch as
-     many incorrect invocations as possible.  */
-  if (sig != SIGSETXID
-      || si->si_pid != __getpid ()
-      || si->si_code != SI_TKILL)
-    return;
-
-  result = INTERNAL_SYSCALL_NCS (__xidcmd->syscall_no, 3, __xidcmd->id[0],
-				 __xidcmd->id[1], __xidcmd->id[2]);
-  int error = 0;
-  if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result)))
-    error = INTERNAL_SYSCALL_ERRNO (result);
-  __nptl_setxid_error (__xidcmd, error);
-
-  /* Reset the SETXID flag.  */
-  struct pthread *self = THREAD_SELF;
-  int flags, newval;
-  do
-    {
-      flags = THREAD_GETMEM (self, cancelhandling);
-      newval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-					  flags & ~SETXID_BITMASK, flags);
-    }
-  while (flags != newval);
-
-  /* And release the futex.  */
-  self->setxid_futex = 1;
-  futex_wake (&self->setxid_futex, 1, FUTEX_PRIVATE);
-
-  if (atomic_decrement_val (&__xidcmd->cntr) == 0)
-    futex_wake ((unsigned int *) &__xidcmd->cntr, 1, FUTEX_PRIVATE);
-}
-
-
 /* When using __thread for this, we do it in libc so as not
    to give libpthread its own TLS segment just for this.  */
 extern void **__libc_dl_error_tsd (void) __attribute__ ((const));
@@ -183,7 +136,7 @@  __pthread_initialize_minimal_internal (void)
   (void) __libc_sigaction (SIGCANCEL, &sa, NULL);
 
   /* Install the handle to change the threads' uid/gid.  */
-  sa.sa_sigaction = sighandler_setxid;
+  sa.sa_sigaction = __nptl_setxid_sighandler;
   sa.sa_flags = SA_SIGINFO | SA_RESTART;
   (void) __libc_sigaction (SIGSETXID, &sa, NULL);
 
diff --git a/nptl/nptl_setxid.c b/nptl/nptl_setxid.c
new file mode 100644
index 0000000000..2f35772411
--- /dev/null
+++ b/nptl/nptl_setxid.c
@@ -0,0 +1,279 @@ 
+/* Copyright (C) 2002-2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <futex-internal.h>
+#include <ldsodefs.h>
+#include <list.h>
+#include <lowlevellock.h>
+#include <pthreadP.h>
+#include <unistd.h>
+
+/* Check for consistency across set*id system call results.  The abort
+   should not happen as long as all privileges changes happen through
+   the glibc wrappers.  ERROR must be 0 (no error) or an errno
+   code.  */
+static void
+setxid_error (struct xid_command *cmdp, int error)
+{
+  do
+    {
+      int olderror = cmdp->error;
+      if (olderror == error)
+        break;
+      if (olderror != -1)
+        {
+          /* Mismatch between current and previous results.  Save the
+             error value to memory so that is not clobbered by the
+             abort function and preserved in coredumps.  */
+          volatile int xid_err __attribute__ ((unused)) = error;
+          abort ();
+        }
+    }
+  while (atomic_compare_and_exchange_bool_acq (&cmdp->error, error, -1));
+}
+
+/* Set by __nptl_setxid and used by __nptl_setxid_sighandler.  */
+static struct xid_command *xidcmd;
+
+/* We use the SIGSETXID signal in the setuid, setgid, etc. implementations to
+   tell each thread to call the respective setxid syscall on itself.  This is
+   the handler.  */
+void
+__nptl_setxid_sighandler (int sig, siginfo_t *si, void *ctx)
+{
+  int result;
+
+  /* Safety check.  It would be possible to call this function for
+     other signals and send a signal from another process.  This is not
+     correct and might even be a security problem.  Try to catch as
+     many incorrect invocations as possible.  */
+  if (sig != SIGSETXID
+      || si->si_pid != __getpid ()
+      || si->si_code != SI_TKILL)
+    return;
+
+  result = INTERNAL_SYSCALL_NCS (xidcmd->syscall_no, 3, xidcmd->id[0],
+				 xidcmd->id[1], xidcmd->id[2]);
+  int error = 0;
+  if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result)))
+    error = INTERNAL_SYSCALL_ERRNO (result);
+  setxid_error (xidcmd, error);
+
+  /* Reset the SETXID flag.  */
+  struct pthread *self = THREAD_SELF;
+  int flags, newval;
+  do
+    {
+      flags = THREAD_GETMEM (self, cancelhandling);
+      newval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
+					  flags & ~SETXID_BITMASK, flags);
+    }
+  while (flags != newval);
+
+  /* And release the futex.  */
+  self->setxid_futex = 1;
+  futex_wake (&self->setxid_futex, 1, FUTEX_PRIVATE);
+
+  if (atomic_decrement_val (&xidcmd->cntr) == 0)
+    futex_wake ((unsigned int *) &xidcmd->cntr, 1, FUTEX_PRIVATE);
+}
+libc_hidden_def (__nptl_setxid_sighandler)
+
+static void
+setxid_mark_thread (struct xid_command *cmdp, struct pthread *t)
+{
+  int ch;
+
+  /* Wait until this thread is cloned.  */
+  if (t->setxid_futex == -1
+      && ! atomic_compare_and_exchange_bool_acq (&t->setxid_futex, -2, -1))
+    do
+      futex_wait_simple (&t->setxid_futex, -2, FUTEX_PRIVATE);
+    while (t->setxid_futex == -2);
+
+  /* Don't let the thread exit before the setxid handler runs.  */
+  t->setxid_futex = 0;
+
+  do
+    {
+      ch = t->cancelhandling;
+
+      /* If the thread is exiting right now, ignore it.  */
+      if ((ch & EXITING_BITMASK) != 0)
+        {
+          /* Release the futex if there is no other setxid in
+             progress.  */
+          if ((ch & SETXID_BITMASK) == 0)
+            {
+              t->setxid_futex = 1;
+              futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
+            }
+          return;
+        }
+    }
+  while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
+                                               ch | SETXID_BITMASK, ch));
+}
+
+
+static void
+setxid_unmark_thread (struct xid_command *cmdp, struct pthread *t)
+{
+  int ch;
+
+  do
+    {
+      ch = t->cancelhandling;
+      if ((ch & SETXID_BITMASK) == 0)
+        return;
+    }
+  while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
+                                               ch & ~SETXID_BITMASK, ch));
+
+  /* Release the futex just in case.  */
+  t->setxid_futex = 1;
+  futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
+}
+
+
+static int
+setxid_signal_thread (struct xid_command *cmdp, struct pthread *t)
+{
+  if ((t->cancelhandling & SETXID_BITMASK) == 0)
+    return 0;
+
+  int val;
+  pid_t pid = __getpid ();
+  val = INTERNAL_SYSCALL_CALL (tgkill, pid, t->tid, SIGSETXID);
+
+  /* If this failed, it must have had not started yet or else exited.  */
+  if (!INTERNAL_SYSCALL_ERROR_P (val))
+    {
+      atomic_increment (&cmdp->cntr);
+      return 1;
+    }
+  else
+    return 0;
+}
+
+int
+attribute_hidden
+__nptl_setxid (struct xid_command *cmdp)
+{
+  int signalled;
+  int result;
+  lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
+
+  xidcmd = cmdp;
+  cmdp->cntr = 0;
+  cmdp->error = -1;
+
+  struct pthread *self = THREAD_SELF;
+
+  /* Iterate over the list with system-allocated threads first.  */
+  list_t *runp;
+  list_for_each (runp, &GL (dl_stack_used))
+    {
+      struct pthread *t = list_entry (runp, struct pthread, list);
+      if (t == self)
+        continue;
+
+      setxid_mark_thread (cmdp, t);
+    }
+
+  /* Now the list with threads using user-allocated stacks.  */
+  list_for_each (runp, &GL (dl_stack_user))
+    {
+      struct pthread *t = list_entry (runp, struct pthread, list);
+      if (t == self)
+        continue;
+
+      setxid_mark_thread (cmdp, t);
+    }
+
+  /* Iterate until we don't succeed in signalling anyone.  That means
+     we have gotten all running threads, and their children will be
+     automatically correct once started.  */
+  do
+    {
+      signalled = 0;
+
+      list_for_each (runp, &GL (dl_stack_used))
+        {
+          struct pthread *t = list_entry (runp, struct pthread, list);
+          if (t == self)
+            continue;
+
+          signalled += setxid_signal_thread (cmdp, t);
+        }
+
+      list_for_each (runp, &GL (dl_stack_user))
+        {
+          struct pthread *t = list_entry (runp, struct pthread, list);
+          if (t == self)
+            continue;
+
+          signalled += setxid_signal_thread (cmdp, t);
+        }
+
+      int cur = cmdp->cntr;
+      while (cur != 0)
+        {
+          futex_wait_simple ((unsigned int *) &cmdp->cntr, cur,
+                             FUTEX_PRIVATE);
+          cur = cmdp->cntr;
+        }
+    }
+  while (signalled != 0);
+
+  /* Clean up flags, so that no thread blocks during exit waiting
+     for a signal which will never come.  */
+  list_for_each (runp, &GL (dl_stack_used))
+    {
+      struct pthread *t = list_entry (runp, struct pthread, list);
+      if (t == self)
+        continue;
+
+      setxid_unmark_thread (cmdp, t);
+    }
+
+  list_for_each (runp, &GL (dl_stack_user))
+    {
+      struct pthread *t = list_entry (runp, struct pthread, list);
+      if (t == self)
+        continue;
+
+      setxid_unmark_thread (cmdp, t);
+    }
+
+  /* This must be last, otherwise the current thread might not have
+     permissions to send SIGSETXID syscall to the other threads.  */
+  result = INTERNAL_SYSCALL_NCS (cmdp->syscall_no, 3,
+                                 cmdp->id[0], cmdp->id[1], cmdp->id[2]);
+  int error = 0;
+  if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result)))
+    {
+      error = INTERNAL_SYSCALL_ERRNO (result);
+      __set_errno (error);
+      result = -1;
+    }
+  setxid_error (cmdp, error);
+
+  lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
+  return result;
+}
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index 14f2bd9535..e091b2ed5e 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -701,8 +701,8 @@  extern void _pthread_cleanup_pop_restore (struct _pthread_cleanup_buffer *buffer
 extern void __nptl_deallocate_tsd (void);
 libc_hidden_proto (__nptl_deallocate_tsd)
 
-extern void __nptl_setxid_error (struct xid_command *cmdp, int error)
-  attribute_hidden;
+void __nptl_setxid_sighandler (int sig, siginfo_t *si, void *ctx);
+libc_hidden_proto (__nptl_setxid_sighandler)
 extern int __nptl_setxid (struct xid_command *cmdp) attribute_hidden;
 
 extern void __nptl_stacks_freeres (void) attribute_hidden;
diff --git a/sysdeps/nptl/pthread-functions.h b/sysdeps/nptl/pthread-functions.h
index 56c746a01c..d76b2cdecf 100644
--- a/sysdeps/nptl/pthread-functions.h
+++ b/sysdeps/nptl/pthread-functions.h
@@ -30,7 +30,6 @@  struct xid_command;
    the thread functions.  */
 struct pthread_functions
 {
-  int (*ptr__nptl_setxid) (struct xid_command *);
 };
 
 /* Variable in libc.so.  */
diff --git a/sysdeps/nptl/setxid.h b/sysdeps/nptl/setxid.h
index 57b665cb5b..8b49d11550 100644
--- a/sysdeps/nptl/setxid.h
+++ b/sysdeps/nptl/setxid.h
@@ -16,6 +16,7 @@ 
    <https://www.gnu.org/licenses/>.  */
 
 #include <nptl/pthreadP.h>
+#include <sys/single_threaded.h>
 #include <sysdep.h>
 
 #define __SETXID_1(cmd, arg1) \
@@ -25,30 +26,10 @@ 
 #define __SETXID_3(cmd, arg1, arg2, arg3) \
   __SETXID_2 (cmd, arg1, arg2); cmd.id[2] = (long int) arg3
 
-#ifdef SINGLE_THREAD
-# define INLINE_SETXID_SYSCALL(name, nr, args...) \
-  INLINE_SYSCALL (name, nr, args)
-#elif defined SHARED
-# define INLINE_SETXID_SYSCALL(name, nr, args...) \
+#define INLINE_SETXID_SYSCALL(name, nr, args...) \
   ({									\
     int __result;							\
-    if (__builtin_expect (__libc_pthread_functions_init, 0))		\
-      {									\
-	struct xid_command __cmd;					\
-	__cmd.syscall_no = __NR_##name;					\
-	__SETXID_##nr (__cmd, args);					\
-	__result = PTHFCT_CALL (ptr__nptl_setxid, (&__cmd));		\
-	}								\
-    else								\
-      __result = INLINE_SYSCALL (name, nr, args);			\
-    __result;								\
-   })
-#else
-# define INLINE_SETXID_SYSCALL(name, nr, args...) \
-  ({									\
-    extern __typeof (__nptl_setxid) __nptl_setxid __attribute__((weak));\
-    int __result;							\
-    if (__glibc_unlikely (__nptl_setxid	!= NULL))			      \
+    if (!__libc_single_threaded)					\
       {									\
 	struct xid_command __cmd;					\
 	__cmd.syscall_no = __NR_##name;					\
@@ -59,4 +40,3 @@ 
       __result = INLINE_SYSCALL (name, nr, args);			\
     __result;								\
    })
-#endif
diff --git a/sysdeps/unix/sysv/linux/internal-signals.h b/sysdeps/unix/sysv/linux/internal-signals.h
index 734989a83a..c44f7019d6 100644
--- a/sysdeps/unix/sysv/linux/internal-signals.h
+++ b/sysdeps/unix/sysv/linux/internal-signals.h
@@ -110,8 +110,4 @@  __libc_signal_restore_set (const sigset_t *set)
   INTERNAL_SYSCALL_CALL (rt_sigprocmask, SIG_SETMASK, set, NULL,
 			 __NSIG_BYTES);
 }
-
-/* Used to communicate with signal handler.  */
-extern struct xid_command *__xidcmd attribute_hidden;
-
 #endif