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    SubjectRe: [PATCH v9 2/8] IMA: add support to measure buffer data hash
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    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.

    >
    > 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".

    There's no need to include the boolean parameter name
    "measure_buf_hash". Please remove it.

    >
    > Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
    > Reviewed-by: Tyler Hicks <tyhicks@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 | 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)".

    > 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

    ^@hash: measure buffer data hash

    > *
    > - * 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

    > + *
    > + * 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.

    > */
    > 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) {
    > + 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

    > + 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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