linux-kernel - Re: [PATCH] KEYS: encrypted: avoid encrypting/decrypting stack buffers

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Message-ID: <20170402033349.GA5346@zzz>
Date:   Sat, 1 Apr 2017 20:33:49 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:     keyrings@...r.kernel.org, David Howells <dhowells@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] KEYS: encrypted: avoid encrypting/decrypting stack
 buffers

On Sat, Apr 01, 2017 at 10:23:57PM -0400, Mimi Zohar wrote:
> On Sat, 2017-04-01 at 12:17 -0700, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@...gle.com>
> > 
> > Since v4.9, the crypto API cannot (normally) be used to encrypt/decrypt
> > stack buffers because the stack may be virtually mapped.  Fix this for
> > the padding buffers in encrypted-keys by using ZERO_PAGE for the
> > encryption padding and by allocating a temporary heap buffer for the
> > decryption padding.
> > 
> > Tested with CONFIG_DEBUG_SG=y:
> > 	keyctl new_session
> > 	keyctl add user master "abcdefghijklmnop" @s
> > 	keyid=$(keyctl add encrypted desc "new user:master 25" @s)
> > 	datablob="$(keyctl pipe $keyid)"
> > 	keyctl unlink $keyid
> > 	keyid=$(keyctl add encrypted desc "load $datablob" @s)
> > 	datablob2="$(keyctl pipe $keyid)"
> > 	[ "$datablob" = "$datablob2" ] && echo "Success!"
> 
> Have you created an encrypted key on a kernel without this patch and
> attempted to load that key on a kernel with this patch?  Does it still
> work?
> 

Yes, a key exported from an unpatched kernel (with DEBUG_SG and DEBUG_VIRTUAL
turned off so it doesn't crash) can be loaded on a patched kernel, then exported
again.  The exported data is identical.

Eric