linux-kernel - Re: [PATCH v4 02/29] rxrpc: Avoid using stack memory in SG lists in rxkad

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Message-ID: <20160628073742.GA15496@gondor.apana.org.au>
Date:	Tue, 28 Jun 2016 15:37:42 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Howells <dhowells@...hat.com>
Cc:	Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>,
	Nadav Amit <nadav.amit@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jann Horn <jann@...jh.net>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v4 02/29] rxrpc: Avoid using stack memory in SG lists in
 rxkad

On Tue, Jun 28, 2016 at 08:32:46AM +0100, David Howells wrote:
> Andy Lutomirski <luto@...nel.org> wrote:
> 
> > @@ -277,6 +277,7 @@ struct rxrpc_connection {
> >  	struct key		*key;		/* security for this connection (client) */
> >  	struct key		*server_key;	/* security for this service */
> >  	struct crypto_skcipher	*cipher;	/* encryption handle */
> > +	struct rxrpc_crypt	csum_iv_head;	/* leading block for csum_iv */
> >  	struct rxrpc_crypt	csum_iv;	/* packet checksum base */
> >  	unsigned long		events;
> >  #define RXRPC_CONN_CHALLENGE	0		/* send challenge packet */
> 
> NAK.  This won't work.  csum_iv_head is per packet being processed, but you've
> put it in rxrpc_connection which is shared amongst several creators/digestors
> of packets.  Putting it in rxrpc_call won't work either since it's also needed
> for connection level packets.

Huh? If you can't write to csum_iv_head without clobbering others
then by the same reasoning you can't write to csum_iv either.  So
unless you're saying the existing code is already broken then there
is nothing wrong with the patch.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt