linux-kernel - Re: [RFC PATCH 2/2] dm-crypt: Use any key type which is registered

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Date:   Sat, 18 Jan 2020 09:55:26 -0800
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Franck LENORMAND <franck.lenormand@....com>,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org
Cc:     horia.geanta@....com, silvano.dininno@....com, agk@...hat.com,
        snitzer@...hat.com, dm-devel@...hat.com, dhowells@...hat.com,
        jmorris@...ei.org, serge@...lyn.com
Subject: Re: [RFC PATCH 2/2] dm-crypt: Use any key type which is registered

On Fri, 2019-03-01 at 17:09 +0100, Franck LENORMAND wrote:
> @@ -2025,16 +2027,15 @@ static int crypt_set_keyring_key(struct
> crypt_config *cc, const char *key_string
>  	if (!key_desc || key_desc == key_string || !strlen(key_desc
> + 1))
>  		return -EINVAL;
>  
> -	if (strncmp(key_string, "logon:", key_desc - key_string + 1)
> &&
> -	    strncmp(key_string, "user:", key_desc - key_string + 1))
> -		return -EINVAL;
> +	type = get_key_type(key_string, key_desc - key_string);
> +	if (!type)
> +		return -ENOENT;

You can't do this.  This check ensures that the key responds correctly
to user_key_payload_locked() lower down.  To do that, the payload has
to be in a specific form.  You ensured that yours are, but dm-crypt
will now accept any key type, load the user payload blindly and create
all sorts of mayhem in the kernel because of the structural differences
in payload types.

James