nptl: Fix abort in case of set*id failure [BZ #17135]

If a call to the set*id functions fails in a multi-threaded program,
the abort introduced in commit 13f7fe35ae
was triggered.

We address by checking that all calls to set*id on all threads give
the same result, and only abort if we see success followed by failure
(or vice versa).

ChangeLog

@@ -1,3 +1,15 @@
+2014-07-10  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #17135]
+	* nptl/pthreadP.h (__nptl_setxid_error): Declare function.
+	* nptl/allocatestack.c (__nptl_setxid_error): New function.
+	(__nptl_setxid): Initialize error member.  Call
+	__nptl_setxid_error.
+	* nptl/nptl-init.c (sighandler_setxid): Call __nptl_setxid_error.
+	* nptl/descr.h (struct xid_command): Add error member.
+	* nptl/tst-setuid3.c: New file.
+	* nptl/Makefile (tests): Add it.
+
 2014-07-10  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
 
 	* sysdeps/unix/sysv/linux/powerpc/lowlevellock.h (__lll_base_trylock):

NEWS

@@ -22,7 +22,7 @@ Version 2.20
   16927, 16928, 16932, 16943, 16958, 16965, 16966, 16967, 16977, 16978,
   16984, 16990, 16996, 17009, 17022, 17031, 17042, 17048, 17050, 17058,
   17061, 17062, 17069, 17075, 17079, 17084, 17086, 17092, 17097, 17125,
-  17137.
+  17135, 17137.
 
 * Optimized strchr implementation for AArch64.  Contributed by ARM Ltd.
 

nptl/Makefile

@@ -271,6 +271,7 @@ tests = tst-typesizes \
 	tst-abstime \
 	tst-vfork1 tst-vfork2 tst-vfork1x tst-vfork2x \
 	tst-getpid1 tst-getpid2 tst-getpid3 \
+	tst-setuid3 \
 	tst-initializers1 $(patsubst %,tst-initializers1-%,c89 gnu89 c99 gnu99)
 xtests = tst-setuid1 tst-setuid1-static tst-setuid2 \
 	tst-mutexpp1 tst-mutexpp6 tst-mutexpp10

nptl/allocatestack.c

@@ -1059,6 +1059,25 @@ setxid_signal_thread (struct xid_command *cmdp, struct pthread *t)
     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.  */
+	abort ();
+    }
+  while (atomic_compare_and_exchange_bool_acq (&cmdp->error, error, -1));
+}
 
 int
 attribute_hidden
@@ -1070,6 +1089,7 @@ __nptl_setxid (struct xid_command *cmdp)
 
   __xidcmd = cmdp;
   cmdp->cntr = 0;
+  cmdp->error = -1;
 
   struct pthread *self = THREAD_SELF;
 
@@ -1153,11 +1173,14 @@ __nptl_setxid (struct xid_command *cmdp)
   INTERNAL_SYSCALL_DECL (err);
   result = INTERNAL_SYSCALL_NCS (cmdp->syscall_no, err, 3,
 				 cmdp->id[0], cmdp->id[1], cmdp->id[2]);
-  if (INTERNAL_SYSCALL_ERROR_P (result, err))
+  int error = 0;
+  if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result, err)))
     {
-      __set_errno (INTERNAL_SYSCALL_ERRNO (result, err));
+      error = INTERNAL_SYSCALL_ERRNO (result, err);
+      __set_errno (error);
       result = -1;
     }
+  __nptl_setxid_error (cmdp, error);
 
   lll_unlock (stack_cache_lock, LLL_PRIVATE);
   return result;

nptl/descr.h

@@ -100,6 +100,7 @@ struct xid_command
   int syscall_no;
   long int id[3];
   volatile int cntr;
+  volatile int error; /* -1: no call yet, 0: success seen, >0: error seen.  */
 };
 
 

nptl/nptl-init.c

@@ -248,10 +248,10 @@ sighandler_setxid (int sig, siginfo_t *si, void *ctx)
   INTERNAL_SYSCALL_DECL (err);
   result = INTERNAL_SYSCALL_NCS (__xidcmd->syscall_no, err, 3, __xidcmd->id[0],
 				 __xidcmd->id[1], __xidcmd->id[2]);
+  int error = 0;
   if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (result, err)))
-    /* Safety check.  This should never happen if the setxid system
+    error = INTERNAL_SYSCALL_ERRNO (result, err);
-       calls are only ever called through their glibc wrappers.  */
+  __nptl_setxid_error (__xidcmd, error);
-    abort ();
 
   /* Reset the SETXID flag.  */
   struct pthread *self = THREAD_SELF;

nptl/pthreadP.h

@@ -578,6 +578,8 @@ extern void _pthread_cleanup_pop_restore (struct _pthread_cleanup_buffer *buffer
 
 extern void __nptl_deallocate_tsd (void) attribute_hidden;
 
+extern void __nptl_setxid_error (struct xid_command *cmdp, int error)
+  attribute_hidden;
 extern int __nptl_setxid (struct xid_command *cmdp) attribute_hidden;
 #ifndef SHARED
 extern void __nptl_set_robust (struct pthread *self);

nptl/tst-setuid3.c

@@ -0,0 +1,104 @@
+/* Copyright (C) 2014 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 <err.h>
+#include <errno.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <unistd.h>
+
+/* The test must run under a non-privileged user ID.  */
+static const uid_t test_uid = 1;
+
+static pthread_barrier_t barrier1;
+static pthread_barrier_t barrier2;
+
+static void *
+thread_func (void *ctx __attribute__ ((unused)))
+{
+  int ret = pthread_barrier_wait (&barrier1);
+  if (ret != PTHREAD_BARRIER_SERIAL_THREAD && ret != 0)
+    errx (1, "pthread_barrier_wait (barrier1) (on thread): %d", ret);
+  ret = pthread_barrier_wait (&barrier2);
+  if (ret != PTHREAD_BARRIER_SERIAL_THREAD && ret != 0)
+    errx (1, "pthread_barrier_wait (barrier2) (on thread): %d", ret);
+  return NULL;
+}
+
+static void
+setuid_failure (int phase)
+{
+  int ret = setuid (0);
+  switch (ret)
+    {
+    case 0:
+      errx (1, "setuid succeeded unexpectedly in phase %d", phase);
+    case -1:
+      if (errno != EPERM)
+	err (1, "setuid phase %d", phase);
+      break;
+    default:
+      errx (1, "invalid setuid return value in phase %d: %d", phase, ret);
+    }
+}
+
+static int
+do_test (void)
+{
+  if (getuid () == 0)
+    if (setuid (test_uid) != 0)
+      err (1, "setuid (%u)", (unsigned) test_uid);
+  if (setuid (getuid ()))
+    err (1, "setuid (getuid ())");
+  setuid_failure (1);
+
+  int ret = pthread_barrier_init (&barrier1, NULL, 2);
+  if (ret != 0)
+    errx (1, "pthread_barrier_init (barrier1): %d", ret);
+  ret = pthread_barrier_init (&barrier2, NULL, 2);
+  if (ret != 0)
+    errx (1, "pthread_barrier_init (barrier2): %d", ret);
+
+  pthread_t thread;
+  ret = pthread_create (&thread, NULL, thread_func, NULL);
+  if (ret != 0)
+    errx (1, "pthread_create: %d", ret);
+
+  /* Ensure that the thread is running properly.  */
+  ret = pthread_barrier_wait (&barrier1);
+  if (ret != 0)
+    errx (1, "pthread_barrier_wait (barrier1): %d", ret);
+
+  setuid_failure (2);
+
+  /* Check success case. */
+  if (setuid (getuid ()) != 0)
+    err (1, "setuid (getuid ())");
+
+  /* Shutdown.  */
+  ret = pthread_barrier_wait (&barrier2);
+  if (ret != PTHREAD_BARRIER_SERIAL_THREAD && ret != 0)
+    errx (1, "pthread_barrier_wait (barrier2): %d", ret);
+
+  if (ret != PTHREAD_BARRIER_SERIAL_THREAD && ret != 0)
+    errx (1, "pthread_join: %d", ret);
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"