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Message-ID: <20201210223854.GG489768@sequoia>
Date: Thu, 10 Dec 2020 16:38:54 -0600
From: Tyler Hicks <tyhicks@...ux.microsoft.com>
To: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
Cc: zohar@...ux.ibm.com, stephen.smalley.work@...il.com,
casey@...aufler-ca.com, agk@...hat.com, snitzer@...hat.com,
gmazyland@...il.com, paul@...l-moore.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 v7 2/8] IMA: add support to measure buffer data hash
On 2020-12-09 11:42:06, Tushar Sugandhi wrote:
> The original IMA buffer data measurement sizes were small (e.g. boot
> command line), but the new buffer data measurement use cases have data
> sizes that are a lot larger. Just as IMA measures the file data hash,
> not the file data, IMA should similarly support the option for measuring
> the hash of the buffer data.
>
> Measuring in-memory buffer-data/buffer-data-hash is different than
> measuring file-data/file-data-hash. For the file, IMA stores the
> measurements in both measurement log and the file's extended attribute -
> which can later be used for appraisal as well. For buffer, the
> measurements are only stored in the IMA log, since the buffer has no
> extended attributes associated with it.
>
> Introduce a boolean parameter measure_buf_hash to support measuring
> hash of a buffer, which would be much smaller, instead of the buffer
> itself.
>
> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
> ---
> security/integrity/ima/ima.h | 3 +-
> security/integrity/ima/ima_appraise.c | 2 +-
> security/integrity/ima/ima_asymmetric_keys.c | 2 +-
> security/integrity/ima/ima_main.c | 36 +++++++++++++++++---
> security/integrity/ima/ima_queue_keys.c | 3 +-
> 5 files changed, 38 insertions(+), 8 deletions(-)
>
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index e5622ce8cbb1..fa3044a7539f 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -268,7 +268,8 @@ void ima_store_measurement(struct integrity_iint_cache *iint, struct file *file,
> struct ima_template_desc *template_desc);
> 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);
> void ima_audit_measurement(struct integrity_iint_cache *iint,
> const unsigned char *filename);
> int ima_alloc_init_template(struct ima_event_data *event_data,
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 8361941ee0a1..46ffa38bab12 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -352,7 +352,7 @@ int ima_check_blacklist(struct integrity_iint_cache *iint,
> if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
> process_buffer_measurement(NULL, digest, digestsize,
> "blacklisted-hash", NONE,
> - pcr, NULL);
> + pcr, NULL, false);
> }
>
> return rc;
> diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> index 1c68c500c26f..a74095793936 100644
> --- a/security/integrity/ima/ima_asymmetric_keys.c
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -60,5 +60,5 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> */
> process_buffer_measurement(NULL, payload, payload_len,
> keyring->description, KEY_CHECK, 0,
> - keyring->description);
> + keyring->description, false);
> }
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index e76ef4bfd0f4..03aad13e9e70 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -779,7 +779,7 @@ int ima_post_load_data(char *buf, loff_t size,
> }
>
> /*
> - * process_buffer_measurement - Measure the buffer to ima log.
> + * process_buffer_measurement - Measure the buffer or the buffer data hash
> * @inode: inode associated with the object being measured (NULL for KEY_CHECK)
> * @buf: pointer to the buffer that needs to be added to the log.
> * @size: size of buffer(in bytes).
> @@ -787,12 +787,23 @@ 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: measure buffer hash
> *
> - * Based on policy, the buffer is measured into the ima log.
> + * Measure the buffer into the IMA log, and extend the @pcr.
> + *
> + * Determine what buffers are allowed to be measured, based on the policy rules
> + * and the IMA hook passed using @func.
> + *
> + * Use @func_data, if provided, to match against the measurement policy rule
> + * data for @func.
> + *
> + * If @measure_buf_hash is set to true - measure hash of the buffer data,
> + * else measure the buffer data itself.
> */
> 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 +818,8 @@ 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 buf_hash[IMA_MAX_DIGEST_SIZE];
> + int buf_hash_len = hash_digest_size[ima_hash_algo];
> int violation = 0;
> int action = 0;
> u32 secid;
> @@ -849,6 +862,20 @@ void process_buffer_measurement(struct inode *inode, const void *buf, int size,
> goto out;
> }
>
> + if (measure_buf_hash) {
> + memcpy(buf_hash, hash.hdr.digest, buf_hash_len);
> +
> + ret = ima_calc_buffer_hash(buf_hash, buf_hash_len,
> + iint.ima_hash);
> + if (ret < 0) {
> + audit_cause = "measure_buf_hash_error";
> + goto out;
> + }
> +
> + event_data.buf = buf_hash;
> + event_data.buf_len = buf_hash_len;
> + }
> +
> ret = ima_alloc_init_template(&event_data, &entry, template);
> if (ret < 0) {
> audit_cause = "alloc_entry";
A few more lines below, not present in this context, is a call to
ima_store_template() with buf as the fourth parameter passed in. That
parameter eventually makes its way to integrity_audit_message() and ends
up as part of an audit message as the value of the "name=" field. This
is usually a filename, the name of a key, or a kexec cmdline. In the
case of measuring SELinux policy, do we want the entire buf to be
included in the audit message?
Tyler
> @@ -890,7 +917,8 @@ void ima_kexec_cmdline(int kernel_fd, const void *buf, int size)
> return;
>
> process_buffer_measurement(file_inode(f.file), buf, size,
> - "kexec-cmdline", KEXEC_CMDLINE, 0, NULL);
> + "kexec-cmdline", KEXEC_CMDLINE, 0, NULL,
> + false);
> fdput(f);
> }
>
> diff --git a/security/integrity/ima/ima_queue_keys.c b/security/integrity/ima/ima_queue_keys.c
> index 69a8626a35c0..c2f2ad34f9b7 100644
> --- a/security/integrity/ima/ima_queue_keys.c
> +++ b/security/integrity/ima/ima_queue_keys.c
> @@ -162,7 +162,8 @@ void ima_process_queued_keys(void)
> entry->payload_len,
> entry->keyring_name,
> KEY_CHECK, 0,
> - entry->keyring_name);
> + entry->keyring_name,
> + false);
> list_del(&entry->list);
> ima_free_key_entry(entry);
> }
> --
> 2.17.1
>
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