linux-kernel - Re: [PATCH v5 2/7] IMA: update process_buffer

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Message-ID: <811fbc4a6f4bd02c77518bd4196d354071145f3e.camel@linux.ibm.com>
Date:   Fri, 06 Nov 2020 07:11:01 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Tushar Sugandhi <tusharsu@...ux.microsoft.com>,
        stephen.smalley.work@...il.com, casey@...aufler-ca.com,
        agk@...hat.com, snitzer@...hat.com, gmazyland@...il.com,
        paul@...l-moore.com
Cc:     tyhicks@...ux.microsoft.com, sashal@...nel.org, jmorris@...ei.org,
        nramas@...ux.microsoft.com, linux-integrity@...r.kernel.org,
        selinux@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: [PATCH v5 2/7] IMA: update process_buffer_measurement to
 measure buffer hash

Hi Tushar,

Below inline are a few additional comments.

> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index ae5da9f3339d..4485d87c0aa5 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -787,12 +787,15 @@ int ima_post_load_data(char *buf, loff_t size,
>   * @func: IMA hook
>   * @pcr: pcr to extend the measurement
>   * @func_data: private data specific to @func, can be NULL.
> + * @measure_buf_hash: if set to true - will measure hash of the buf,
> + *                    instead of buf
>   *
>   * Based on policy, the buffer is measured into the ima log.

Both the brief and longer function descriptions need to be updated, as
well as the last argument description.  The last argument should be
limited to "measure buffer hash".  How it is used could be included in
the longer function description.  The longer function description would
include adding the buffer data or the buffer data hash to the IMA
measurement list and extending the PCR.  

For example, 
process_buffer_measurement - measure the buffer data or the buffer data
hash


>   */
>  void process_buffer_measurement(struct inode *inode, const void *buf, int size,
>  				const char *eventname, enum ima_hooks func,
> -				int pcr, const char *func_data)
> +				int pcr, const char *func_data,
> +				bool measure_buf_hash)
>  {
>  	int ret = 0;
>  	const char *audit_cause = "ENOMEM";
> @@ -807,6 +810,8 @@ void process_buffer_measurement(struct inode *inode, const void *buf, int size,
>  		struct ima_digest_data hdr;
>  		char digest[IMA_MAX_DIGEST_SIZE];
>  	} hash = {};
> +	char digest_hash[IMA_MAX_DIGEST_SIZE];
> +	int hash_len = hash_digest_size[ima_hash_algo];
>  	int violation = 0;
>  	int action = 0;
>  	u32 secid;
> @@ -855,6 +860,21 @@ void process_buffer_measurement(struct inode *inode, const void *buf, int size,
>  		goto out;
>  	}
>  
> +	if (measure_buf_hash) {
> +		memcpy(digest_hash, hash.hdr.digest, hash_len);

Instead of digest_hash and hash_len, consider naming the variables
buf_hash and buf_hashlen.

> +
> +		ret = ima_calc_buffer_hash(digest_hash,
> +					   hash_len,
> +					   iint.ima_hash);

There's no need for each variable to be on a separate line.

thanks,

Mimi

> +		if (ret < 0) {
> +			audit_cause = "measure_buf_hash_error";
> +			goto out;
> +		}
> +
> +		event_data.buf = digest_hash;
> +		event_data.buf_len = hash_len;
> +	}
> +
>  	ret = ima_alloc_init_template(&event_data, &entry, template);
>  	if (ret < 0) {
>  		audit_cause = "alloc_entry";