[PATCH] Use __pthread_attr_copy in mq_notify (bug 27896)

Make a deep copy of the pthread attribute object to remove a potential
use-after-free issue.

From 217b6dc298156bdb0d6aea9ea93e7e394a5ff091 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Tue, 1 Jun 2021 17:51:41 +0200
Subject: [PATCH] Fix use of __pthread_attr_copy in mq_notify (bug 27896)

__pthread_attr_copy can fail and does not initialize the attribute
structure in that case.

If __pthread_attr_copy is never called and there is no allocated
attribute, pthread_attr_destroy should not be called, otherwise
there is a null pointer dereference in rt/tst-mqueue6.

Fixes commit 42d359350510506b87101cf77202fefcbfc790cb
("Use __pthread_attr_copy in mq_notify (bug 27896)").

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
From b805aebd42364fe696e417808a700fdb9800c9e8 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npv1310@gmail.com>
Date: Mon, 9 Aug 2021 20:17:34 +0530
Subject: [PATCH] librt: fix NULL pointer dereference (bug 28213)

Helper thread frees copied attribute on NOTIFY_REMOVED message
received from the OS kernel.  Unfortunately, it fails to check whether
copied attribute actually exists (data.attr != NULL).  This worked
earlier because free() checks passed pointer before actually
attempting to release corresponding memory.  But
__pthread_attr_destroy assumes pointer is not NULL.

So passing NULL pointer to __pthread_attr_destroy will result in
segmentation fault.  This scenario is possible if
notification->sigev_notify_attributes == NULL (which means default
thread attributes should be used).

Signed-off-by: Nikita Popov <npv1310@gmail.com>
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
From 4cc79c217744743077bf7a0ec5e0a4318f1e6641 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npv1310@gmail.com>
Date: Thu, 12 Aug 2021 16:09:50 +0530
Subject: [PATCH] librt: add test (bug 28213)

This test implements following logic:
1) Create POSIX message queue.
   Register a notification with mq_notify (using NULL attributes).
   Then immediately unregister the notification with mq_notify.
   Helper thread in a vulnerable version of glibc
   should cause NULL pointer dereference after these steps.
2) Once again, register the same notification.
   Try to send a dummy message.
   Test is considered successfulif the dummy message
   is successfully received by the callback function.

Signed-off-by: Nikita Popov <npv1310@gmail.com>
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Gbp-Pq: Topic all
Gbp-Pq: Name git-CVE-2021-33574-mq_notify-use-after-free.diff

diff --git a/rt/Makefile b/rt/Makefile
index 6d6b896ee9817c5cb4962b6ee08ac6d59d043cb6..caffd5392586ab8022dde4fd9be282fd26811a0b 100644 (file)
--- a/rt/Makefile
+++ b/rt/Makefile
@@ -50,6 +50,7 @@ tests := tst-shm tst-clock tst-clock_nanosleep tst-timer tst-timer2 \
         tst-aio7 tst-aio8 tst-aio9 tst-aio10 \
         tst-mqueue1 tst-mqueue2 tst-mqueue3 tst-mqueue4 \
         tst-mqueue5 tst-mqueue6 tst-mqueue7 tst-mqueue8 tst-mqueue9 \
+        tst-bz28213 \
         tst-timer3 tst-timer4 tst-timer5 \
         tst-cpuclock1 tst-cpuclock2 \
         tst-cputimer1 tst-cputimer2 tst-cputimer3 \

diff --git a/rt/tst-bz28213.c b/rt/tst-bz28213.c
new file mode 100644 (file)
index 0000000..0c096b5
--- /dev/null
+++ b/rt/tst-bz28213.c
@@ -0,0 +1,101 @@
+/* Bug 28213: test for NULL pointer dereference in mq_notify.
+   Copyright (C) The GNU Toolchain Authors.
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <mqueue.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+
+static mqd_t m = -1;
+static const char msg[] = "hello";
+
+static void
+check_bz28213_cb (union sigval sv)
+{
+  char buf[sizeof (msg)];
+
+  (void) sv;
+
+  TEST_VERIFY_EXIT ((size_t) mq_receive (m, buf, sizeof (buf), NULL)
+                   == sizeof (buf));
+  TEST_VERIFY_EXIT (memcmp (buf, msg, sizeof (buf)) == 0);
+
+  exit (0);
+}
+
+static void
+check_bz28213 (void)
+{
+  struct sigevent sev;
+
+  memset (&sev, '\0', sizeof (sev));
+  sev.sigev_notify = SIGEV_THREAD;
+  sev.sigev_notify_function = check_bz28213_cb;
+
+  /* Step 1: Register & unregister notifier.
+     Helper thread should receive NOTIFY_REMOVED notification.
+     In a vulnerable version of glibc, NULL pointer dereference follows. */
+  TEST_VERIFY_EXIT (mq_notify (m, &sev) == 0);
+  TEST_VERIFY_EXIT (mq_notify (m, NULL) == 0);
+
+  /* Step 2: Once again, register notification.
+     Try to send one message.
+     Test is considered successful, if the callback does exit (0). */
+  TEST_VERIFY_EXIT (mq_notify (m, &sev) == 0);
+  TEST_VERIFY_EXIT (mq_send (m, msg, sizeof (msg), 1) == 0);
+
+  /* Wait... */
+  pause ();
+}
+
+static int
+do_test (void)
+{
+  static const char m_name[] = "/bz28213_queue";
+  struct mq_attr m_attr;
+
+  memset (&m_attr, '\0', sizeof (m_attr));
+  m_attr.mq_maxmsg = 1;
+  m_attr.mq_msgsize = sizeof (msg);
+
+  m = mq_open (m_name,
+               O_RDWR | O_CREAT | O_EXCL,
+               0600,
+               &m_attr);
+
+  if (m < 0)
+    {
+      if (errno == ENOSYS)
+        FAIL_UNSUPPORTED ("POSIX message queues are not implemented\n");
+      FAIL_EXIT1 ("Failed to create POSIX message queue: %m\n");
+    }
+
+  TEST_VERIFY_EXIT (mq_unlink (m_name) == 0);
+
+  check_bz28213 ();
+
+  return 0;
+}
+
+#include <support/test-driver.c>

diff --git a/sysdeps/unix/sysv/linux/mq_notify.c b/sysdeps/unix/sysv/linux/mq_notify.c
index 3563e82cd4f4b5522401eb76ff94e712b26c1953..69b8db4d48181040e46fe51145d364620094df4e 100644 (file)
--- a/sysdeps/unix/sysv/linux/mq_notify.c
+++ b/sysdeps/unix/sysv/linux/mq_notify.c
@@ -134,9 +134,12 @@ helper_thread (void *arg)
               to wait until it is done with it.  */
            (void) __pthread_barrier_wait (&notify_barrier);
        }
-      else if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_REMOVED)
-       /* The only state we keep is the copy of the thread attributes.  */
-       free (data.attr);
+      else if (data.raw[NOTIFY_COOKIE_LEN - 1] == NOTIFY_REMOVED && data.attr != NULL)
+       {
+         /* The only state we keep is the copy of the thread attributes.  */
+         pthread_attr_destroy (data.attr);
+         free (data.attr);
+       }
     }
   return NULL;
 }
@@ -215,6 +218,39 @@ init_mq_netlink (void)
 }
 
 
+static int __pthread_attr_copy(pthread_attr_t *target, const pthread_attr_t *source)
+{
+  /* Avoid overwriting *TARGET until all allocations have
+     succeeded.  */
+  union {
+      pthread_attr_t external;
+      struct pthread_attr internal;
+  } temp;
+  temp.external = *source;
+
+  /* Force new allocation.  This function has full ownership of temp.  */
+  temp.internal.cpuset = NULL;
+  temp.internal.cpusetsize = 0;
+
+  struct pthread_attr *isource = (struct pthread_attr *) source;
+
+  /* Propagate affinity mask information.  */
+  if (isource->cpusetsize > 0) {
+    /* inline pthread_attr_setaffinity_np, otherwise we break conformance tests */
+    temp.internal.cpuset = malloc (isource->cpusetsize);
+    if (temp.internal.cpuset == NULL)
+      return ENOMEM;
+    temp.internal.cpusetsize = isource->cpusetsize;
+    memcpy(temp.internal.cpuset, isource->cpuset, isource->cpusetsize);
+  }
+
+  /* Transfer ownership.  *target is not assumed to have been
+     initialized.  */
+  *target = temp.external;
+  return 0;
+}
+
+
 /* Register notification upon message arrival to an empty message queue
    MQDES.  */
 int
@@ -257,8 +293,14 @@ mq_notify (mqd_t mqdes, const struct sigevent *notification)
       if (data.attr == NULL)
        return -1;
 
-      memcpy (data.attr, notification->sigev_notify_attributes,
-             sizeof (pthread_attr_t));
+      int ret = __pthread_attr_copy (data.attr,
+                                    notification->sigev_notify_attributes);
+      if (ret != 0)
+       {
+         free (data.attr);
+         __set_errno (ret);
+         return -1;
+       }
     }
 
   /* Construct the new request.  */
@@ -271,8 +313,11 @@ mq_notify (mqd_t mqdes, const struct sigevent *notification)
   int retval = INLINE_SYSCALL (mq_notify, 2, mqdes, &se);
 
   /* If it failed, free the allocated memory.  */
-  if (__glibc_unlikely (retval != 0))
-    free (data.attr);
+  if (retval != 0 && data.attr != NULL)
+    {
+      pthread_attr_destroy (data.attr);
+      free (data.attr);
+    }
 
   return retval;
 }