[PATCH] Fix use of __pthread_attr_copy in mq_notify (bug 27896)

[Siddhesh Poyarekar]

On 6/1/21 11:18 PM, Florian Weimer via Libc-alpha wrote:
> __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)").
> 
> Tested on i686-linux-gnu and x86_64-linux-gnu.

Thanks, I missed that in my review.  LGTM.

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

> 
> ---
>   sysdeps/unix/sysv/linux/mq_notify.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/mq_notify.c b/sysdeps/unix/sysv/linux/mq_notify.c
> index f7ddfe5a6c..6f46d29d1d 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);
>