Check for syscall error in the SETXID implementation in NPTL (bug 13347).

At this point, we can only abort the process because we have already
switched credentials on other threads.  Returning an error would still
leave the process in an inconsistent state.

The new xtest needs root privileges to run.

4 files changed, 161 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index edb6ec4..1ef37c7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2014-04-01  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #13347]
+	* nptl/nptl-init.c (sighandler_setxid): Check system call result.
+	* nptl/tst-setuid2.c: New file.
+	* nptl/Makefile (xtests): Add tst-setuid2.
+
 2014-04-01  Alan Modra  <amodra@gmail.com>
 
 	[BZ #16786]
diff --git a/nptl/Makefile b/nptl/Makefile
index 897ac96..2876224 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -270,7 +270,8 @@ tests = tst-typesizes \
 	tst-vfork1 tst-vfork2 tst-vfork1x tst-vfork2x \
 	tst-getpid1 tst-getpid2 tst-getpid3 \
 	tst-initializers1 $(patsubst %,tst-initializers1-%,c89 gnu89 c99 gnu99)
-xtests = tst-setuid1 tst-setuid1-static tst-mutexpp1 tst-mutexpp6 tst-mutexpp10
+xtests = tst-setuid1 tst-setuid1-static tst-setuid2 \
+	tst-mutexpp1 tst-mutexpp6 tst-mutexpp10
 test-srcs = tst-oddstacklimit
 
 # Files which must not be linked with libpthread.
diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index 794156b..2796dc5 100644
--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -232,6 +232,7 @@ sighandler_setxid (int sig, siginfo_t *si, void *ctx)
   /* Determine the process ID.  It might be negative if the thread is
      in the middle of a fork() call.  */
   pid_t pid = THREAD_GETMEM (THREAD_SELF, pid);
+  int result;
   if (__glibc_unlikely (pid < 0))
     pid = -pid;
 
@@ -245,8 +246,12 @@ sighandler_setxid (int sig, siginfo_t *si, void *ctx)
     return;
 
   INTERNAL_SYSCALL_DECL (err);
-  INTERNAL_SYSCALL_NCS (__xidcmd->syscall_no, err, 3, __xidcmd->id[0],
-			__xidcmd->id[1], __xidcmd->id[2]);
+  result = INTERNAL_SYSCALL_NCS (__xidcmd->syscall_no, err, 3, __xidcmd->id[0],
+				 __xidcmd->id[1], __xidcmd->id[2]);
+  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 ();
 
   /* Reset the SETXID flag.  */
   struct pthread *self = THREAD_SELF;
diff --git a/nptl/tst-setuid2.c b/nptl/tst-setuid2.c
new file mode 100644
index 0000000..951aecc
--- /dev/null
+++ b/nptl/tst-setuid2.c
@@ -0,0 +1,145 @@
+/* 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 <errno.h>
+#include <pthread.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+/* Check that a partial setuid failure aborts the process. */
+
+static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t cond_send;
+static void (*func_sent) (void);
+static pthread_cond_t cond_recv;
+
+#define FAIL(fmt, ...) \
+  do { printf ("FAIL: " fmt "\n", __VA_ARGS__); _exit (1); } while (0)
+
+static void *
+thread_func (void *ctx __attribute__ ((unused)))
+{
+  int ret = pthread_mutex_lock (&mutex);
+  if (ret != 0)
+    FAIL ("pthread_mutex_lock (thread): %d", ret);
+
+  while (true)
+    {
+      if (func_sent != NULL)
+	{
+	  void (*func) (void) = func_sent;
+	  ret = pthread_mutex_unlock (&mutex);
+	  if (ret != 0)
+	    FAIL ("pthread_mutex_unlock (thread): %d", ret);
+	  func ();
+	  ret = pthread_mutex_lock (&mutex);
+	  if (ret != 0)
+	    FAIL ("pthread_mutex_lock (thread): %d", ret);
+	  func_sent = NULL;
+	  ret = pthread_cond_signal (&cond_recv);
+	  if (ret != 0)
+	    FAIL ("pthread_cond_signal (recv): %d", ret);
+	}
+      ret = pthread_cond_wait (&cond_send, &mutex);
+      if (ret != 0)
+	FAIL ("pthread_cond_wait (send): %d", ret);
+    }
+  return NULL;
+}
+
+static void
+run_on_thread (void (*func) (void))
+{
+  int ret = pthread_mutex_lock (&mutex);
+  if (ret != 0)
+    FAIL ("pthread_mutex_lock (%s): %d", __func__, ret);
+  func_sent = func;
+  ret = pthread_mutex_unlock (&mutex);
+  if (ret != 0)
+    FAIL ("pthread_mutex_unlock (%s): %d", __func__, ret);
+
+  ret = pthread_cond_signal (&cond_send);
+  if (ret != 0)
+    FAIL ("pthread_mutex_lock (%s): %d", __func__, ret);
+
+  ret = pthread_mutex_lock (&mutex);
+  if (ret != 0)
+    FAIL ("pthread_mutex_lock (%s): %d", __func__, ret);
+
+  while (func_sent != NULL)
+    {
+      ret = pthread_cond_wait (&cond_recv, &mutex);
+      if (ret != 0)
+	FAIL ("pthread_mutex_wait (%s): %d", __func__, ret);
+    }
+  ret = pthread_mutex_unlock (&mutex);
+  if (ret != 0)
+    FAIL ("pthread_mutex_unlock (%s): %d", __func__, ret);
+}
+
+static void
+change_thread_ids (void)
+{
+  long ret = syscall (__NR_setresuid, 2001, 2002, 2003);
+  if (ret != 0)
+    FAIL ("setresuid (2001, 2002, 2003): %ld", ret);
+}
+
+static uid_t ruid, euid, suid;
+
+static void
+get_thread_ids (void)
+{
+  if (getresuid (&ruid, &euid, &suid) < 0)
+    FAIL ("getresuid: %m (%d)", errno);
+}
+
+static void
+abort_expected (int signal __attribute__ ((unused)))
+{
+  _exit (0);
+}
+
+static int
+do_test (void)
+{
+  pthread_t thread;
+  int ret = pthread_create (&thread, NULL, thread_func, NULL);
+  if (ret != 0)
+    FAIL ("pthread_create: %d", ret);
+
+  run_on_thread (change_thread_ids);
+
+  signal (SIGABRT, &abort_expected);
+  /* This should abort the process.  */
+  if (setresuid (1001, 1002, 1003) < 0)
+    FAIL ("setresuid: %m (%d)", errno);
+  signal (SIGABRT, SIG_DFL);
+
+  /* If we get here, check that the kernel did the right thing. */
+  run_on_thread (get_thread_ids);
+  if (ruid != 1001 || euid != 1002 || euid != 1003)
+    FAIL ("unexpected UIDs after setuid: %ld, %ld, %ld",
+	  (long) ruid, (long) euid, (long) suid);
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"