[RFC PATCH 1/3] dm ima: allow targets to remeasure their table entry

[Thore Sommer <public@thson.de>]

A new DM event dm_target_update is introduced for targets to remeasure
their table entry. This is intended for targets that indicate security
relevant events by updating one of their table entries (e.g. verity for
corruption).

In the event the dm version, device metadata and target data gets
measured.

This does not update the hash of the active table because it would require
to rehash the whole table with all the other targets entries.

Signed-off-by: Thore Sommer <public@thson.de>
---
 drivers/md/dm-ima.c | 76 +++++++++++++++++++++++++++++++++++++++++++++
 drivers/md/dm-ima.h |  2 ++
 2 files changed, 78 insertions(+)

diff --git a/drivers/md/dm-ima.c b/drivers/md/dm-ima.c
index 957999998d70..3b1bb97263d9 100644
--- a/drivers/md/dm-ima.c
+++ b/drivers/md/dm-ima.c
@@ -750,3 +750,79 @@ void dm_ima_measure_on_device_rename(struct mapped_device *md)
 	kfree(new_dev_name);
 	kfree(new_dev_uuid);
 }
+
+/*
+ * Give the option for targets to remeasure on state change.
+ */
+void dm_ima_measure_on_target_update(struct dm_target *ti)
+{
+	char *ima_buf = NULL, *target_metadata_buf = NULL, *target_data_buf = NULL;
+	struct dm_target *ti2;
+	size_t target_metadata_buf_len, target_data_buf_len;
+	unsigned int num_targets, target_index;
+	struct dm_table *table = ti->table;
+	struct mapped_device *md = table->md;
+	bool found = false;
+	bool noio = true;
+	int l = 0;
+
+	ima_buf = dm_ima_alloc(DM_IMA_MEASUREMENT_BUF_LEN, GFP_KERNEL, noio);
+	if (!ima_buf)
+		return;
+
+	target_metadata_buf = dm_ima_alloc(DM_IMA_TARGET_METADATA_BUF_LEN, GFP_KERNEL, noio);
+	if (!target_metadata_buf)
+		goto exit;
+
+	target_data_buf = dm_ima_alloc(DM_IMA_TARGET_DATA_BUF_LEN, GFP_KERNEL, noio);
+	if (!target_data_buf)
+		goto exit;
+
+	/*
+	 * Get the index of the target in the table.
+	 */
+	num_targets = dm_table_get_num_targets(table);
+	for (target_index = 0; target_index < num_targets; target_index++) {
+		ti2 = dm_table_get_target(table, target_index);
+		if (!ti)
+			goto exit;
+		if (ti == ti2) {
+			found = true;
+			break;
+		}
+	}
+	if (!found)
+		goto exit;
+
+	scnprintf(target_metadata_buf, DM_IMA_TARGET_METADATA_BUF_LEN,
+			  "target_index=%d,target_begin=%llu,target_len=%llu,",
+			  target_index, ti->begin, ti->len);
+	target_metadata_buf_len = strlen(target_metadata_buf);
+
+	if (ti->type->status)
+		ti->type->status(ti, STATUSTYPE_IMA, STATUSTYPE_IMA, target_data_buf,
+					DM_IMA_TARGET_DATA_BUF_LEN);
+	else
+		target_data_buf[0] = '\0';
+	target_data_buf_len = strlen(target_data_buf);
+
+	memcpy(ima_buf + l, DM_IMA_VERSION_STR, md->ima.dm_version_str_len);
+	l += md->ima.dm_version_str_len;
+
+	memcpy(ima_buf + l, md->ima.active_table.device_metadata,
+	       md->ima.active_table.device_metadata_len);
+	l += md->ima.active_table.device_metadata_len;
+
+	memcpy(ima_buf + l, target_metadata_buf, target_metadata_buf_len);
+	l += target_metadata_buf_len;
+
+	memcpy(ima_buf + l, target_data_buf, target_data_buf_len);
+
+	dm_ima_measure_data("dm_target_update", ima_buf, strlen(ima_buf), noio);
+
+exit:
+	kfree(ima_buf);
+	kfree(target_data_buf);
+	kfree(target_metadata_buf);
+}
+EXPORT_SYMBOL_GPL(dm_ima_measure_on_target_update);
diff --git a/drivers/md/dm-ima.h b/drivers/md/dm-ima.h
index b8c3b614670b..281a8b65f8a9 100644
--- a/drivers/md/dm-ima.h
+++ b/drivers/md/dm-ima.h
@@ -63,6 +63,7 @@ void dm_ima_measure_on_device_resume(struct mapped_device *md, bool swap);
 void dm_ima_measure_on_device_remove(struct mapped_device *md, bool remove_all);
 void dm_ima_measure_on_table_clear(struct mapped_device *md, bool new_map);
 void dm_ima_measure_on_device_rename(struct mapped_device *md);
+void dm_ima_measure_on_target_update(struct dm_target *ti);
 
 #else
 
@@ -72,6 +73,7 @@ static inline void dm_ima_measure_on_device_resume(struct mapped_device *md, boo
 static inline void dm_ima_measure_on_device_remove(struct mapped_device *md, bool remove_all) {}
 static inline void dm_ima_measure_on_table_clear(struct mapped_device *md, bool new_map) {}
 static inline void dm_ima_measure_on_device_rename(struct mapped_device *md) {}
+static inline void dm_ima_measure_on_target_update(struct dm_target *ti) {}
 
 #endif /* CONFIG_IMA */
 
-- 
2.34.1