linux-kernel - Re: [PATCH v6 2/5] ima: define a new template field named 'd-ngv2' and templates

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Date:   Mon, 21 Mar 2022 15:48:51 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>,
        linux-integrity@...r.kernel.org
Cc:     Eric Biggers <ebiggers@...nel.org>, linux-fscrypt@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/5] ima: define a new template field named 'd-ngv2'
 and templates

On Mon, 2022-03-21 at 08:53 -0400, Stefan Berger wrote:
> >   	/*
> >   	 * digest formats:
> >   	 *  - DATA_FMT_DIGEST: digest
> >   	 *  - DATA_FMT_DIGEST_WITH_ALGO: [<hash algo>] + ':' + '\0' + digest,
> > +	 *  - DATA_FMT_DIGEST_WITH_TYPE_AND_ALGO:
> > +	 *	[<digest type> + ':' + <hash algo>] + ':' + '\0' + digest,
> > +	 *    where <hash type> is either "ima" or "verity",
> >   	 *    where <hash algo> is provided if the hash algorithm is not
> >   	 *    SHA1 or MD5
> >   	 */
> > -	u8 buffer[CRYPTO_MAX_ALG_NAME + 2 + IMA_MAX_DIGEST_SIZE] = { 0 };
> > +	u8 buffer[DIGEST_TYPE_MAXLEN + CRYPTO_MAX_ALG_NAME + 2 +
> > +		IMA_MAX_DIGEST_SIZE] = { 0 };
> 
> Should it not be DIGEST_TYPE_MAXLEN + 1 /* for ':' */ + 
> CRYPTO_MAX_ALG_NAME + ....

DIGEST_TYPE_MAXLEN is hard coded as 16.

> 
> >   	enum data_formats fmt = DATA_FMT_DIGEST;
> >   	u32 offset = 0;
> >   
> > -	if (hash_algo < HASH_ALGO__LAST) {
> > -		fmt = DATA_FMT_DIGEST_WITH_ALGO;
> > -		offset += snprintf(buffer, CRYPTO_MAX_ALG_NAME + 1, "%s",
> > +	if (digest_type < digest_type_size && hash_algo < HASH_ALGO__LAST) {
> 
> It's a bit difficult to see what the digest_type has to do with size...
> Maybe digest_type should be a enum and the comparison here should be 
> digest_type != DIGEST_TYPE_NONE or something like it..

digest_type_size is the size of the array.  It's defined as "static int
digest_type_size = ARRAY_SIZE(digest_type_name);", with the first
element as "ima".

> > +
> > +/*
> > + * This function writes the digest of an event (without size limit),
> > + * prefixed with both the hash type and algorithm.
> > + */
> > +int ima_eventdigest_ngv2_init(struct ima_event_data *event_data,
> > +			      struct ima_field_data *field_data)
> > +{
> > +	u8 *cur_digest = NULL, hash_algo = HASH_ALGO_SHA1;
> > +	u32 cur_digestsize = 0;
> > +	u8 digest_type = 0;
> 
> What does '0' mean? I think this should definitely be an enum or at 
> least #define.

The first element of the array is "ima".  Should I define two macros
similar to kernel_read_file_id and kernel_read_file_str for just two
strings?

thanks,

Mimi