Fix setxid race with thread creation

nptl/ChangeLog

@@ -1,3 +1,14 @@
+2010-03-05  Andreas Schwab  <schwab@redhat.com>
+	    Ulrich Drepper  <drepper@redhat.com>
+
+	* allocatestack.c (setxid_mark_thread): Delay handling of thread if
+	it is creating a thread or it is just being created.
+	* pthread_create.c (start_thread): Wake setxid thread if it is
+	waiting.
+	(__pthread_create_2_1): Initialize setxid_futex.
+	* sysdeps/pthread/createthread.c (do_clone): Wake setxid thread if it
+	is waiting.
+
 2010-01-15  Ulrich Drepper  <drepper@redhat.com>
 
 	* sysdeps/unix/sysv/linux/i386/i486/pthread_cond_timedwait.S:

nptl/allocatestack.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 2002-2007, 2009 Free Software Foundation, Inc.
+/* Copyright (C) 2002-2007, 2009, 2010 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
 
@@ -380,7 +380,7 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
 			       - TLS_TCB_SIZE - adj);
 #elif TLS_DTV_AT_TP
       pd = (struct pthread *) (((uintptr_t) attr->stackaddr
-			        - __static_tls_size - adj)
+				- __static_tls_size - adj)
 			       - TLS_PRE_TCB_SIZE);
 #endif
 
@@ -546,7 +546,7 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
 #ifndef __ASSUME_PRIVATE_FUTEX
 	  /* The thread must know when private futexes are supported.  */
 	  pd->header.private_futex = THREAD_GETMEM (THREAD_SELF,
-                                                    header.private_futex);
+						    header.private_futex);
 #endif
 
 #ifdef NEED_DL_SYSINFO
@@ -969,6 +969,13 @@ 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
+      lll_futex_wait (&t->setxid_futex, -2, LLL_PRIVATE);
+    while (t->setxid_futex == -2);
+
   /* Don't let the thread exit before the setxid handler runs.  */
   t->setxid_futex = 0;
 

nptl/pthread_create.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 2002-2007,2008,2009 Free Software Foundation, Inc.
+/* Copyright (C) 2002-2007,2008,2009,2010 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
 
@@ -239,6 +239,10 @@ start_thread (void *arg)
   /* Initialize resolver state pointer.  */
   __resp = &pd->res;
 
+  /* Allow setxid from now onwards.  */
+  if (__builtin_expect (atomic_exchange_acq (&pd->setxid_futex, 0) == -2, 0))
+    lll_futex_wake (&pd->setxid_futex, 1, LLL_PRIVATE);
+
 #ifdef __NR_set_robust_list
 # ifndef __ASSUME_SET_ROBUST_LIST
   if (__set_robust_list_avail >= 0)
@@ -538,6 +542,9 @@ __pthread_create_2_1 (newthread, attr, start_routine, arg)
 	}
     }
 
+  /* Don't allow setxid until cloned. */
+  pd->setxid_futex = -1;
+
   /* Pass the descriptor to the caller.  */
   *newthread = (pthread_t) pd;
 

nptl/sysdeps/pthread/createthread.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 2002-2007, 2008 Free Software Foundation, Inc.
+/* Copyright (C) 2002-2007, 2008, 2010 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
 
@@ -28,7 +28,7 @@
 #include "kernel-features.h"
 
 
-#define CLONE_SIGNAL    	(CLONE_SIGHAND | CLONE_THREAD)
+#define CLONE_SIGNAL		(CLONE_SIGHAND | CLONE_THREAD)
 
 /* Unless otherwise specified, the thread "register" is going to be
    initialized with a pointer to the TCB.  */
@@ -72,8 +72,14 @@ do_clone (struct pthread *pd, const struct pthread_attr *attr,
      that cares whether the thread count is correct.  */
   atomic_increment (&__nptl_nthreads);
 
-  if (ARCH_CLONE (fct, STACK_VARIABLES_ARGS, clone_flags,
+  int rc = ARCH_CLONE (fct, STACK_VARIABLES_ARGS, clone_flags,
-		  pd, &pd->tid, TLS_VALUE, &pd->tid) == -1)
+		       pd, &pd->tid, TLS_VALUE, &pd->tid);
+
+  /* Allow setxid from now onwards.  */
+  if (__builtin_expect (atomic_exchange_acq (&pd->setxid_futex, 0) == -2, 0))
+    lll_futex_wake (&pd->setxid_futex, 1, LLL_PRIVATE);
+
+  if (__builtin_expect (rc == -1, 0))
     {
       atomic_decrement (&__nptl_nthreads); /* Oops, we lied for a second.  */