[PATCH v3 6/6] IMA: validate supported kernel data sources before measurement

[Tushar Sugandhi]

Currently, IMA does not restrict random data sources from measuring their
data using ima_measure_critical_data(). Any kernel data source can call
the function, and it's data will get measured as long as the input
event_data_source is part of the IMA policy -
CRITICAL_DATA+critical_kernel_data_sources. This may result in IMA log
getting bloated by random data sources. Supporting random data sources
at run-time may also impact the reliability of the system. 

To ensure that only data from supported sources are measured, the kernel
component needs to be added to a compile-time list of supported sources
(an "allowed list of components") in ima.h. IMA then validates the input
parameter - event_data_source passed to ima_measure_critical_data()
against this allowed list at run-time.

Provide an infrastructure for kernel data sources to be added to
the supported data sources list at compile-time. Update
ima_measure_critical_data() to validate, at run-time, that the data
source is supported before measuring the data.
Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
---
 security/integrity/ima/ima.h      | 29 +++++++++++++++++++++++++++++
 security/integrity/ima/ima_main.c |  3 +++
 2 files changed, 32 insertions(+)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 00b84052c8f1..ecb0a1e7378f 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -228,6 +228,35 @@ extern const char *const func_tokens[];
 
 struct modsig;
 
+#define __ima_supported_kernel_data_sources(source)	\
+	source(MIN_SOURCE, min_source)			\
+	source(MAX_SOURCE, max_source)
+
+#define __ima_enum_stringify(ENUM, str) (#str),
+
+enum ima_supported_kernel_data_sources {
+	__ima_supported_kernel_data_sources(__ima_hook_enumify)
+};
+
+static const char * const ima_supported_kernel_data_sources_str[] = {
+	__ima_supported_kernel_data_sources(__ima_enum_stringify)
+};
+
+static inline bool ima_kernel_data_source_is_supported(const char *source)
+{
+	int i;
+
+	if (!source)
+		return false;
+
+	for (i = MIN_SOURCE + 1; i < MAX_SOURCE; i++) {
+		if (!strcmp(ima_supported_kernel_data_sources_str[i], source))
+			return true;
+	}
+
+	return false;
+}
+
 #ifdef CONFIG_IMA_QUEUE_EARLY_BOOT_KEYS
 /*
  * To track keys that need to be measured.
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index a889bf40cb7e..41be4d1d839e 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -888,6 +888,9 @@ int ima_measure_critical_data(const char *event_name,
 	if (!event_name || !event_data_source || !buf || !buf_len)
 		return -EINVAL;
 
+	if (!ima_kernel_data_source_is_supported(event_data_source))
+		return -EPERM;
+
 	return process_buffer_measurement(NULL, buf, buf_len, event_name,
 					  CRITICAL_DATA, 0, event_data_source,
 					  measure_buf_hash);
-- 
2.17.1