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

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Date:   Thu, 2 Jul 2020 13:26:53 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, ast@...nel.org,
        axboe@...nel.dk, bfields@...ldses.org,
        bridge@...ts.linux-foundation.org, chainsaw@...too.org,
        christian.brauner@...ntu.com, chuck.lever@...cle.com,
        davem@...emloft.net, dhowells@...hat.com,
        gregkh@...uxfoundation.org, jarkko.sakkinen@...ux.intel.com,
        jmorris@...ei.org, josh@...htriplett.org, keescook@...omium.org,
        keyrings@...r.kernel.org, kuba@...nel.org,
        lars.ellenberg@...bit.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-security-module@...r.kernel.org, nikolay@...ulusnetworks.com,
        philipp.reisner@...bit.com, ravenexp@...il.com,
        roopa@...ulusnetworks.com, serge@...lyn.com, slyfox@...too.org,
        viro@...iv.linux.org.uk, yangtiezhu@...ngson.cn,
        netdev@...r.kernel.org, markward@...ux.ibm.com,
        linux-s390 <linux-s390@...r.kernel.org>
Subject: Re: linux-next: umh: fix processed error when UMH_WAIT_PROC is used
 seems to break linux bridge on s390x (bisected)

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 */
>