linux-next: umh: fix processed error when UMH_WAIT_PROC is used seems to break linux bridge on s390x (bisected)

[Tetsuo Handa]

On 2020/07/02 0:38, Luis Chamberlain wrote:
> @@ -156,6 +156,18 @@ static void call_usermodehelper_exec_sync(struct subprocess_info *sub_info)
>  		 */
>  		if (KWIFEXITED(ret))
>  			sub_info->retval = KWEXITSTATUS(ret);
> +		/*
> +		 * Do we really want to be passing the signal, or do we pass
> +		 * a single error code for all cases?
> +		 */
> +		else if (KWIFSIGNALED(ret))
> +			sub_info->retval = KWTERMSIG(ret);

No, this is bad. Caller of usermode helper is unable to distinguish exit(9)
and e.g. SIGKILL'ed by the OOM-killer. Please pass raw exit status value.

I feel that caller of usermode helper should not use exit status value.
For example, call_sbin_request_key() is checking

  test_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags) || key_validate(key) < 0

condition (if usermode helper was invoked) in order to "ignore any errors from
userspace if the key was instantiated".

> +		/* Same here */
> +		else if (KWIFSTOPPED((ret)))
> +			sub_info->retval = KWSTOPSIG(ret);
> +		/* And are we really sure we want this? */
> +		else if (KWIFCONTINUED((ret)))
> +			sub_info->retval = 0;
>  	}
>  
>  	/* Restore default kernel sig handler */
>