linux-kernel - Re: [PATCH] key: Convert big

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Message-ID: <20170508221943.GA46762@gmail.com>
Date:   Mon, 8 May 2017 15:19:43 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] key: Convert big_key payload.data to struct

On Mon, May 08, 2017 at 11:00:56PM +0100, David Howells wrote:
> Kees Cook <keescook@...omium.org> wrote:
> 
> > There is a lot of needless casting happening in the big_key data payload.
> > This is harder to trivially verify by static analysis and specifically
> > the randstruct GCC plugin (which was unhappy about casting a struct
> > path across two entries of a void * array). This converts the payload to
> > the actually used structures (one pointer, one embedded struct, and one
> > size_t).
> 
> I'd really rather not do this as this moves the definition of an individual
> key type into the general structure (I know I've done this for the keyring
> type, but that's a special part of the keyring code).  That's the start of the
> slippery slope into moving all of them in there.
> 
> I'd rather you defined, say:
> 
> 	struct big_key_payload {
> 		u8		*key_data;
> 		struct path	key_path;
> 		size_t		key_len;
> 	};
> 
> in big_key.c and cast &key->payload to it.
> 

That still seems like a hack.  It probably would be easier to kmalloc() this
struct and store a pointer to it in key->payload.data[0], like some of the other
key types do, e.g. "encrypted" and "trusted".  The key data could even be inline
at the end, for non-file backed big_keys.

Eric