Messages in this thread | | | Subject | Re: [PATCH v7 2/8] IMA: add support to measure buffer data hash | From | Tushar Sugandhi <> | Date | Thu, 10 Dec 2020 17:21:19 -0800 |
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On 2020-12-10 2:38 p.m., Tyler Hicks wrote: > 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@linux.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 > Great catch. We obviously don't want to include the entire buf in the audit message, especially when the measure_buf_hash is set to true. (the buffer being measured is expected to be large in that case)
How about the following? Does it look ok to you? Mimi?
if (measure_buf_hash) ret = ima_store_template(entry, violation, NULL, buf_hash, pcr); else ret = ima_store_template(entry, violation, NULL, buf, pcr);
~Tushar
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