[PATCH] Use __pthread_attr_copy in mq_notify (bug 27896)

[Siddhesh Poyarekar]

On 6/1/21 2:20 PM, Andreas Schwab wrote:
> Make a deep copy of the pthread attribute object to remove a potential
> use-after-free issue.

LGTM

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

> ---
>   NEWS                                |  4 ++++
>   sysdeps/unix/sysv/linux/mq_notify.c | 15 ++++++++++-----
>   2 files changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/NEWS b/NEWS
> index 266837bf2d..4460752df7 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -56,6 +56,10 @@ Security related changes:
>     potentially resulting in degraded service or Denial of Service on the
>     local system.  Reported by Chris Schanzle.
>   
> +  CVE-2021-33574: The mq_notify function has a potential use-after-free
> +  issue when using a notification type of SIGEV_THREAD and a thread
> +  attribute with a non-default affinity mask.
> +
>   The following bugs are resolved with this release:
>   
>     [The release manager will add the list generated by
> diff --git a/sysdeps/unix/sysv/linux/mq_notify.c b/sysdeps/unix/sysv/linux/mq_notify.c
> index cc575a0cdd..f7ddfe5a6c 100644
> --- a/sysdeps/unix/sysv/linux/mq_notify.c
> +++ b/sysdeps/unix/sysv/linux/mq_notify.c
> @@ -133,8 +133,11 @@ helper_thread (void *arg)
>   	    (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);
> +	{
> +	  /* The only state we keep is the copy of the thread attributes.  */
> +	  pthread_attr_destroy (data.attr);
> +	  free (data.attr);
> +	}
>       }
>     return NULL;
>   }
> @@ -255,8 +258,7 @@ 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));
> +      __pthread_attr_copy (data.attr, notification->sigev_notify_attributes);
>       }
>   
>     /* Construct the new request.  */
> @@ -270,7 +272,10 @@ mq_notify (mqd_t mqdes, const struct sigevent *notification)
>   
>     /* If it failed, free the allocated memory.  */
>     if (__glibc_unlikely (retval != 0))
> -    free (data.attr);
> +    {
> +      pthread_attr_destroy (data.attr);
> +      free (data.attr);
> +    }
>   
>     return retval;
>   }
>