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 13f7fe35ae2b0ea55dc4b9628763aafdc8bdc30c
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).

6 files changed, 136 insertions, 5 deletions

diff --git a/nptl/Makefile b/nptl/Makefile
index 67f7d5b..ab3080e 100644
--- a/nptl/Makefile
+++ b/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
diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 9095ef4..d95ffe9 100644
--- a/nptl/allocatestack.c
+++ b/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;
diff --git a/nptl/descr.h b/nptl/descr.h
index 61d57d5..6738591 100644
--- a/nptl/descr.h
+++ b/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.  */
 };
 
 
diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index 2796dc5..9f7b20a 100644
--- a/nptl/nptl-init.c
+++ b/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
-       calls are only ever called through their glibc wrappers.  */
-    abort ();
+    error = INTERNAL_SYSCALL_ERRNO (result, err);
+  __nptl_setxid_error (__xidcmd, error);
 
   /* Reset the SETXID flag.  */
   struct pthread *self = THREAD_SELF;
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index 197401a..94e7890 100644
--- a/nptl/pthreadP.h
+++ b/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);
diff --git a/nptl/tst-setuid3.c b/nptl/tst-setuid3.c
new file mode 100644
index 0000000..f78f485
--- /dev/null
+++ b/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"