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Message-ID: <3fdb72ae-f291-386b-e7b9-688dfe092dc5@linux.microsoft.com>
Date: Tue, 5 Jan 2021 10:53:04 -0800
From: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
To: Mimi Zohar <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
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 v9 2/8] IMA: add support to measure buffer data hash
On 2020-12-23 4:03 p.m., Mimi Zohar wrote:
> On Sat, 2020-12-12 at 10:02 -0800, 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.
>
> By definition, buffer data is only measured. Nothing new is added by
> the above paragraph. Please remove it.
>
Sure. Will remove.
>>
>> Introduce a boolean parameter measure_buf_hash to support measuring
>> hash of a buffer, which would be much smaller, instead of the buffer
>> itself.
>
> Like the patch Subject line use "the buffer data hash" instead of the
> "hash of a buffer".
>
Will do.
> There's no need to include the boolean parameter name
> "measure_buf_hash". Please remove it.
>
Will do.
>>
>> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>> Reviewed-by: Tyler Hicks <tyhicks@...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 | 38 +++++++++++++++++---
>> security/integrity/ima/ima_queue_keys.c | 3 +-
>> 5 files changed, 39 insertions(+), 9 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);
>
> Please abbreviate the boolean name to "hash". The test would then be
> "if (hash == true)" or "if (hash)".
>
Will do.
>> 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..0f8409d77602 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
>
> ^@...h: measure buffer data hash
>
Agreed. Will fix.
>> *
>> - * Based on policy, the buffer is measured into the ima log.
>> + * Measure the buffer into the IMA log, and extend the @pcr.
>
> IMA always measures/appraises files and measures buffer data based on
> policy. The above sentence succintly summarizes what
> process_buffer_measurement() does. This patch adds support for
> measuring the "buffer data hash". The following would be an
> appropriate change.
>
> * Based on policy, either the buffer data or buffer data hash is
> measured
>
Sounds good. Will update.
>> + *
>> + * 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.
>
> This patch should be limited to adding "buffer data hash" support.
> These changes don't belong in this patch. Please remove.
>
Agreed. Will remove.
>> */
>> 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;
>> @@ -849,13 +862,27 @@ void process_buffer_measurement(struct inode *inode, const void *buf, int size,
>> goto out;
>> }
>>
>> + if (measure_buf_hash) {
>
> ^ if (hash) {
Yes.
>> + 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";
>
> I don't see a good no reason for defining a new audit cause. Use the
> existing "hashing_error".
>
> thanks,
>
> Mimi
>
Thanks,
Tushar
>> + 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";
>> goto out;
>> }
>>
>> - ret = ima_store_template(entry, violation, NULL, buf, pcr);
>> + ret = ima_store_template(entry, violation, NULL, event_data.buf, pcr);
>> if (ret < 0) {
>> audit_cause = "store_entry";
>> ima_free_template_entry(entry);
>> @@ -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);
>> }
>
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