commit 8c06748c51750333d1516a2d342ed2361186e908
Author: Florian Weimer <fweimer@redhat.com>
Date:   Tue Jun 1 17:51:41 2021 +0200

    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>
    (cherry picked from commit 217b6dc298156bdb0d6aea9ea93e7e394a5ff091)

diff --git a/sysdeps/unix/sysv/linux/mq_notify.c b/sysdeps/unix/sysv/linux/mq_notify.c
index f7ddfe5a6c1c2766..6f46d29d1dcb6acc 100644
--- a/sysdeps/unix/sysv/linux/mq_notify.c
+++ b/sysdeps/unix/sysv/linux/mq_notify.c
@@ -258,7 +258,14 @@ mq_notify (mqd_t mqdes, const struct sigevent *notification)
       if (data.attr == NULL)
 	return -1;
 
-      __pthread_attr_copy (data.attr, notification->sigev_notify_attributes);
+      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.  */
@@ -271,7 +278,7 @@ 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))
+  if (retval != 0 && data.attr != NULL)
     {
       pthread_attr_destroy (data.attr);
       free (data.attr);