linux-kernel - Re: [EXTERNAL] [PATCH v2 2/6] lib: Expand asn1_encode

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Date: Tue, 21 May 2024 09:21:13 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Bharat Bhushan" <bbhushan2@...vell.com>, "Herbert Xu"
 <herbert@...dor.apana.org.au>
Cc: "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
 "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
 "Andreas.Fuchs@...ineon.com" <Andreas.Fuchs@...ineon.com>, "James
 Prestwood" <prestwoj@...il.com>, "David Woodhouse" <dwmw2@...radead.org>,
 "Eric Biggers" <ebiggers@...nel.org>, "James Bottomley"
 <James.Bottomley@...senpartnership.com>, "David S. Miller"
 <davem@...emloft.net>, "open list:CRYPTO API"
 <linux-crypto@...r.kernel.org>, "open list" <linux-kernel@...r.kernel.org>,
 "Andrew Morton" <akpm@...ux-foundation.org>, "James Bottomley"
 <James.Bottomley@...senPartnership.com>, "Mimi Zohar"
 <zohar@...ux.ibm.com>, "David Howells" <dhowells@...hat.com>, "Paul Moore"
 <paul@...l-moore.com>, "James Morris" <jmorris@...ei.org>, "Serge E.
 Hallyn" <serge@...lyn.com>, "open list:SECURITY SUBSYSTEM"
 <linux-security-module@...r.kernel.org>
Subject: Re: [EXTERNAL] [PATCH v2 2/6] lib: Expand asn1_encode_integer() to
 variable size integers

On Tue May 21, 2024 at 8:36 AM EEST, Bharat Bhushan wrote:
> > -	data_len -= 2;
> > +	(*data++) = _tag(UNIV, PRIM, INT);
>
> Just for my clarification: 
> 	First index of "data" is updated here with tag and data pointer incremented.
> 	Next comment for continuation
>
> > +	data_len--;
> > 
> > -	data[0] = _tag(UNIV, PRIM, INT);
> > -	if (integer == 0) {
> > -		*d++ = 0;
> > -		goto out;
> > +	if (!memchr_inv(integer, 0, integer_len)) {
> > +		data[1] = 1;
> > +		data[2] = 0;
> > +		return &data[2];
>
> Here we are effectively setting second and third index of original
> "data" pointer as "data" pointer was incremented earlier.
> So second index of original "data" pointer is not touched. Also
> returning 3rd index pointer of original data pointer
>
> Is that intentional?

No! I read the diff few times, and I think you have a point.

Indices should be 0 (length) and 1 (value). I.e. it forms an encoded
version of zero. The last index what it should be, i.e. return address
of the next byte after the encoded integer.

Thanks for pointing this out.

> Thanks
> -Bharat

BR, Jarkko