[RFC][PATCH v4 6/9] ima: Store verified usage in digest cache based on integrity metadata flags

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu at huawei.com>

The Integrity Digest Cache allows integrity providers to record how the
digest list being used to populate the digest cache was verified.

Integrity providers can register a kernel_post_read_file LSM hook
implementation, and call digest_cache_verif_set() providing the result of
the digest list verification, together with the digest list file
descriptor.

IMA implements ima_digest_cache_store_verified_usage(), storing the
verified usage of the digest cache based on whether or not the digest list
the digest cache is being populated from was measured/appraised.

If the digest list was measured (IMA_MEASURED set in iint->flags),
ima_digest_cache_store_verified_usage() sets the
IMA_DIGEST_CACHE_MEASURE_DATA in the verified usage. If the digest list was
appraised (IMA_APPRAISED_SUBMASK), ima_digest_cache_store_verified_usage()
sets the IMA_DIGEST_CACHE_APPRAISE_DATA in the verified usage.

Verified usage based on integrity metadata will be ANDed with the policy
usage from the IMA policy. Then, the final decision will ultimately depend
on whether or not the calculated digest of the accessed file was found in
the digest cache.

ANDing the verified usage with the policy usage prevents remote verifiers
from receiving an incomplete IMA measurement list, where measurements of
files are skipped, but there isn't the measurement of the digest lists the
calculated file digests were searched into. It also prevents successful
appraisal without appraising the digest list itself.

Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
---
 security/integrity/ima/ima_digest_cache.c | 35 +++++++++++++++++++++++
 security/integrity/ima/ima_digest_cache.h |  7 +++++
 security/integrity/ima/ima_main.c         |  2 ++
 3 files changed, 44 insertions(+)

diff --git a/security/integrity/ima/ima_digest_cache.c b/security/integrity/ima/ima_digest_cache.c
index ad47772a05bd..2c7824ce05cd 100644
--- a/security/integrity/ima/ima_digest_cache.c
+++ b/security/integrity/ima/ima_digest_cache.c
@@ -47,3 +47,38 @@ bool ima_digest_cache_get_check(struct file *file,
 	digest_cache_put(digest_cache);
 	return false;
 }
+
+/**
+ * ima_digest_cache_store_verified_usage - Store verified usage in digest cache
+ * @file: Digest list file descriptor
+ * @iint: Inode integrity metadata
+ *
+ * Set digest cache verified usage in the digest cache associated to the
+ * digest list file descriptor. Verified usage is based on whether or not the
+ * digest list was measured/appraised, and is ANDed with the policy usage to
+ * make the final decision on whether a digest cache can be used for a specific
+ * IMA action.
+ */
+void ima_digest_cache_store_verified_usage(struct file *file,
+					   struct ima_iint_cache *iint)
+{
+	u64 verified_usage = 0;
+	int rc;
+
+	if (iint->flags & IMA_MEASURED)
+		verified_usage |= IMA_DIGEST_CACHE_MEASURE_DATA;
+	if (iint->flags & IMA_APPRAISED_SUBMASK)
+		verified_usage |= IMA_DIGEST_CACHE_APPRAISE_DATA;
+
+	/*
+	 * Set digest cache verified usage from integrity metadata flags for
+	 * later use.
+	 */
+	rc = digest_cache_verif_set(file, "ima", &verified_usage,
+				    sizeof(verified_usage));
+
+	/* Ignore if fd doesn't have digest cache set (prefetching). */
+	if (rc && rc != -ENOENT)
+		pr_debug("Cannot set verified usage for %s, ret: %d, ignoring\n",
+			 file_dentry(file)->d_name.name, rc);
+}
diff --git a/security/integrity/ima/ima_digest_cache.h b/security/integrity/ima/ima_digest_cache.h
index 8126ae1e2f4f..167690930078 100644
--- a/security/integrity/ima/ima_digest_cache.h
+++ b/security/integrity/ima/ima_digest_cache.h
@@ -12,6 +12,8 @@
 #ifdef CONFIG_INTEGRITY_DIGEST_CACHE
 bool ima_digest_cache_get_check(struct file *file,
 				struct ima_iint_cache *iint);
+void ima_digest_cache_store_verified_usage(struct file *file,
+					   struct ima_iint_cache *iint);
 #else
 static inline bool ima_digest_cache_get_check(struct file *file,
 					      struct ima_iint_cache *iint)
@@ -19,4 +21,9 @@ static inline bool ima_digest_cache_get_check(struct file *file,
 	return false;
 }
 
+static inline void
+ima_digest_cache_store_verified_usage(struct file *file,
+				      struct ima_iint_cache *iint)
+{ }
+
 #endif /* CONFIG_INTEGRITY_DIGEST_CACHE */
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index aaff8cd8d5c6..607749d520b0 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -421,6 +421,8 @@ static int process_measurement(struct file *file, const struct cred *cred,
 	if ((mask & MAY_WRITE) && test_bit(IMA_DIGSIG, &iint->atomic_flags) &&
 	     !(iint->flags & IMA_NEW_FILE))
 		rc = -EACCES;
+	if (!rc && func == DIGEST_LIST_CHECK)
+		ima_digest_cache_store_verified_usage(file, iint);
 	mutex_unlock(&iint->mutex);
 	kfree(xattr_value);
 	ima_free_modsig(modsig);
-- 
2.47.0.118.gfd3785337b