From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0E48C43603 for ; Mon, 9 Dec 2019 08:50:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8029A2075B for ; Mon, 9 Dec 2019 08:50:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="pIqxcd8/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727047AbfLIIu4 (ORCPT ); Mon, 9 Dec 2019 03:50:56 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:45276 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726377AbfLIIuz (ORCPT ); Mon, 9 Dec 2019 03:50:55 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Mime-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=raDwZdXhm/ocslieiRqQr7D9redw49APKKDGB7Zg8wI=; b=pIqxcd8/sr2wZL/AgRWq2juLk xpEoZaDjLzrEgC+WReMce/FRTSIg6OztbiBBPWQoTDy/hN+el7nxLHdgHIEk/+kQ3TFkPrxc9VF1w AnTmLJh56nsw1ZuUnxWOl4FEVqp51NyJ1wiAqnZpogl3TMtZ3r5JgBheHwj1X9xucz3EAAlppKYs/ KaXb3Olqg6UCIirE0U8ChE6P+7CIACW5TYiLepYIVAHXc+575VHbPM8QcyQbCIum4cW3Z2TC7pC14 voppPcvTcXhPFif8/orjO3lJPD7gcDA2TbCM5Y8uES4XmT5nrg6/lUbNo28alFrn1YTwiT9R2iebW xq0meKHbA==; Received: from 54-240-197-228.amazon.com ([54.240.197.228] helo=freeip.amazon.com) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1ieEko-0005UU-U4; Mon, 09 Dec 2019 08:50:55 +0000 Message-ID: <8391d7c97e2897ec7e0ba2a30de272f7a0dd1ec3.camel@infradead.org> Subject: Re: [PATCH 2/8] lib: add asn.1 encoder From: David Woodhouse To: James Bottomley , linux-integrity@vger.kernel.org Cc: Mimi Zohar , Jarkko Sakkinen , David Howells Date: Mon, 09 Dec 2019 08:50:52 +0000 In-Reply-To: <1575781706.14069.10.camel@HansenPartnership.com> References: <1575781600.14069.8.camel@HansenPartnership.com> <1575781706.14069.10.camel@HansenPartnership.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-3ac79ANoe95FEgd07bCJ" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.1 Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org --=-3ac79ANoe95FEgd07bCJ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sat, 2019-12-07 at 21:08 -0800, James Bottomley wrote: > +/** > + * asn1_encode_integer - encode positive integer to ASN.1 > + * @_data: pointer to the pointer to the data > + * @integer: integer to be encoded > + * > + * This is a simplified encoder: since we know the integer is > + * positive we don't have to bother with twos complement and since we > + * know the largest integer is a u64, we know the max length is 8. > + */ > +void asn1_encode_integer(unsigned char **_data, u64 integer) > +{ > + unsigned char *data =3D *_data, *d =3D &data[2]; > + int i; > + bool found =3D false; > + > + data[0] =3D _tag(UNIV, PRIM, INT); > + if (integer =3D=3D 0) { > + *d++ =3D 0; > + goto out; > + } > + for (i =3D sizeof(integer); i > 0 ; i--) { > + int byte =3D integer >> (8*(i-1)); > + > + if (!found && byte =3D=3D 0) > + continue; > + found =3D true; > + if (byte & 0x80) > + *d++ =3D 0; > + *d++ =3D byte; > + } > + out: > + data[1] =3D d - data - 2; > + *_data =3D d; > +} I'd be a lot happier to see a 'buffer length' argument here. This API is ju= st one accidental u64 underflow away from a caller which "knows" its <128 i= nteger is only three bytes long, actually taking eleven and overflowing its= buffer. Especially since you are actively encouraging people to create fr= agments on the stack and then assemble them into SEQUENCES later (qv=C2=B9)= . Also: is documenting it as taking a 'positive integer' enough? Making that explicit in the function name might be more likely to prevent future users from assuming it actually encodes an arbitrary INTEGER. > +static void asn1_encode_definite_length(unsigned char **data, u32 len) > +{ > + if (len <=3D 0x7f) { > + *((*data)++) =3D len; > + return; > + } > + if (len <=3D 0xff) { > + *((*data)++) =3D 0x81; > + *((*data)++) =3D len & 0xff; > + return; > + } > + if (len <=3D 0xffff) { > + *((*data)++) =3D 0x82; > + *((*data)++) =3D (len >> 8) & 0xff; > + *((*data)++) =3D len & 0xff; > + return; > + } > + > + if (WARN(len > 0xffffff, "ASN.1 length can't be > 0xffffff")) > + return; > + > + *((*data)++) =3D 0x83; > + *((*data)++) =3D (len >> 16) & 0xff; > + *((*data)++) =3D (len >> 8) & 0xff; > + *((*data)++) =3D len & 0xff; > +} (=C2=B9) That's nice when you know the length in advance. Less so when you don't, because you have to either calculate it first or actually create the whole of the content in a separate buffer and copy it around. It would be useful to permit sequences with indeterminate length. You could even return a pointer which allows them to be changed to definite length if they are <128 bytes at the end. I note that later in this series in tpm2_encode_policy() you are eschewing your own API for this, and doing just what I said above =E2=80=94 going back and filling in the length later. > +/** > + * asn1_encode_tag - add a tag for optional or explicit value > + * @data: pointer to place tag at > + * @tag: tag to be placed > + * @string: the data to be tagged > + * @len: the length of the data to be tagged > + * > + * Note this currently only handles short form tags < 31 > + */ > +void asn1_encode_tag(unsigned char **data, u32 tag, > + const unsigned char *string, u32 len) > +{ > + if (WARN(tag > 30, "ASN.1 tag can't be > 30")) > + return; > + > + *((*data)++) =3D _tagn(CONT, CONS, tag); > + asn1_encode_definite_length(data, len); > + memcpy(*data, string, len); > + *data +=3D len; > +} > +EXPORT_SYMBOL(asn1_encode_tag); EXPORT_SYMBOL() again when everything else here uses EXPORT_SYMBOL_GPL(). --=-3ac79ANoe95FEgd07bCJ Content-Type: application/x-pkcs7-signature; name="smime.p7s" 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