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>
(cherry picked from commit b805aebd42364fe696e417808a700fdb9800c9e8)

diff --git a/sysdeps/unix/sysv/linux/mq_notify.c b/sysdeps/unix/sysv/linux/mq_notify.c
index 9799dcdaa479a1d56495c0474214e370332df655..eccae2e4c6cdfefa77fb12a0821ac66a23cf5007 100644 (file)
--- a/sysdeps/unix/sysv/linux/mq_notify.c
+++ b/sysdeps/unix/sysv/linux/mq_notify.c
@@ -131,7 +131,7 @@ 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)
+      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);