dm ima: measure data on table load

DM configures a block device with various target specific attributes
passed to it as a table.  DM loads the table, and calls each target’s
respective constructors with the attributes as input parameters.
Some of these attributes are critical to ensure the device meets
certain security bar.  Thus, IMA should measure these attributes, to
ensure they are not tampered with, during the lifetime of the device.
So that the external services can have high confidence in the
configuration of the block-devices on a given system.

Some devices may have large tables.  And a given device may change its
state (table-load, suspend, resume, rename, remove, table-clear etc.)
many times.  Measuring these attributes each time when the device
changes its state will significantly increase the size of the IMA logs.
Further, once configured, these attributes are not expected to change
unless a new table is loaded, or a device is removed and recreated.
Therefore the clear-text of the attributes should only be measured
during table load, and the hash of the active/inactive table should be
measured for the remaining device state changes.

Export IMA function ima_measure_critical_data() to allow measurement
of DM device parameters, as well as target specific attributes, during
table load.  Compute the hash of the inactive table and store it for
measurements during future state change.  If a load is called multiple
times, update the inactive table hash with the hash of the latest
populated table.  So that the correct inactive table hash is measured
when the device transitions to different states like resume, remove,
rename, etc.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com> # leak fix
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 330 insertions, 0 deletions

diff --git a/drivers/md/dm-ima.c b/drivers/md/dm-ima.c
new file mode 100644
index 000000000000..c8f54d9f6c8d
--- /dev/null
+++ b/drivers/md/dm-ima.c
@@ -0,0 +1,330 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 Microsoft Corporation
+ *
+ * Author: Tushar Sugandhi <tusharsu@linux.microsoft.com>
+ *
+ * File: dm-ima.c
+ *       Enables IMA measurements for DM targets
+ */
+
+#include "dm-core.h"
+#include "dm-ima.h"
+
+#include <linux/ima.h>
+#include <crypto/hash.h>
+#include <linux/crypto.h>
+#include <crypto/hash_info.h>
+
+#define DM_MSG_PREFIX "ima"
+
+/*
+ * Internal function to prefix separator characters in input buffer with escape
+ * character, so that they don't interfere with the construction of key-value pairs,
+ * and clients can split the key1=val1,key2=val2,key3=val3; pairs properly.
+ */
+static void fix_separator_chars(char **buf)
+{
+	int l = strlen(*buf);
+	int i, j, sp = 0;
+
+	for (i = 0; i < l; i++)
+		if ((*buf)[i] == '\\' || (*buf)[i] == ';' || (*buf)[i] == '=' || (*buf)[i] == ',')
+			sp++;
+
+	if (!sp)
+		return;
+
+	for (i = l-1, j = i+sp; i >= 0; i--) {
+		(*buf)[j--] = (*buf)[i];
+		if ((*buf)[i] == '\\' || (*buf)[i] == ';' || (*buf)[i] == '=' || (*buf)[i] == ',')
+			(*buf)[j--] = '\\';
+	}
+}
+
+/*
+ * Internal function to allocate memory for IMA measurements.
+ */
+static void *dm_ima_alloc(size_t len, gfp_t flags, bool noio)
+{
+	unsigned int noio_flag;
+	void *ptr;
+
+	if (noio)
+		noio_flag = memalloc_noio_save();
+
+	ptr = kzalloc(len, flags);
+
+	if (noio)
+		memalloc_noio_restore(noio_flag);
+
+	return ptr;
+}
+
+/*
+ * Internal function to allocate and copy name and uuid for IMA measurements.
+ */
+static int dm_ima_alloc_and_copy_name_uuid(struct mapped_device *md, char **dev_name,
+					   char **dev_uuid, bool noio)
+{
+	int r;
+	*dev_name = dm_ima_alloc(DM_NAME_LEN*2, GFP_KERNEL, noio);
+	if (!(*dev_name)) {
+		r = -ENOMEM;
+		goto error;
+	}
+
+	*dev_uuid = dm_ima_alloc(DM_UUID_LEN*2, GFP_KERNEL, noio);
+	if (!(*dev_uuid)) {
+		r = -ENOMEM;
+		goto error;
+	}
+
+	r = dm_copy_name_and_uuid(md, *dev_name, *dev_uuid);
+	if (r)
+		goto error;
+
+	fix_separator_chars(dev_name);
+	fix_separator_chars(dev_uuid);
+
+	return 0;
+error:
+	kfree(*dev_name);
+	kfree(*dev_uuid);
+	*dev_name = NULL;
+	*dev_uuid = NULL;
+	return r;
+}
+
+/*
+ * Internal function to allocate and copy device data for IMA measurements.
+ */
+static int dm_ima_alloc_and_copy_device_data(struct mapped_device *md, char **device_data,
+					     unsigned int num_targets, bool noio)
+{
+	char *dev_name = NULL, *dev_uuid = NULL;
+	int r;
+
+	r = dm_ima_alloc_and_copy_name_uuid(md, &dev_name, &dev_uuid, noio);
+	if (r)
+		return r;
+
+	*device_data = dm_ima_alloc(DM_IMA_DEVICE_BUF_LEN, GFP_KERNEL, noio);
+	if (!(*device_data)) {
+		r = -ENOMEM;
+		goto error;
+	}
+
+	scnprintf(*device_data, DM_IMA_DEVICE_BUF_LEN,
+		  "name=%s,uuid=%s,major=%d,minor=%d,minor_count=%d,num_targets=%u;",
+		  dev_name, dev_uuid, md->disk->major, md->disk->first_minor,
+		  md->disk->minors, num_targets);
+error:
+	kfree(dev_name);
+	kfree(dev_uuid);
+	return r;
+}
+
+/*
+ * Internal wrapper function to call IMA to measure DM data.
+ */
+static void dm_ima_measure_data(const char *event_name, const void *buf, size_t buf_len,
+				bool noio)
+{
+	unsigned int noio_flag;
+
+	if (noio)
+		noio_flag = memalloc_noio_save();
+
+	ima_measure_critical_data(DM_NAME, event_name, buf, buf_len, false);
+
+	if (noio)
+		memalloc_noio_restore(noio_flag);
+}
+
+/*
+ * Initialize/reset the dm ima related data structure variables.
+ */
+void dm_ima_reset_data(struct mapped_device *md)
+{
+	memset(&(md->ima), 0, sizeof(md->ima));
+}
+
+/*
+ * Build up the IMA data for each target, and finally measure.
+ */
+void dm_ima_measure_on_table_load(struct dm_table *table, unsigned int status_flags)
+{
+	size_t device_data_buf_len, target_metadata_buf_len, target_data_buf_len, l = 0;
+	char *target_metadata_buf = NULL, *target_data_buf = NULL, *digest_buf = NULL;
+	char *ima_buf = NULL, *device_data_buf = NULL;
+	int digest_size, last_target_measured = -1, r;
+	status_type_t type = STATUSTYPE_IMA;
+	size_t cur_total_buf_len = 0;
+	unsigned int num_targets, i;
+	SHASH_DESC_ON_STACK(shash, NULL);
+	struct crypto_shash *tfm = NULL;
+	u8 *digest = NULL;
+	bool noio = false;
+
+	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 error;
+
+	target_data_buf = dm_ima_alloc(DM_IMA_TARGET_DATA_BUF_LEN, GFP_KERNEL, noio);
+	if (!target_data_buf)
+		goto error;
+
+	num_targets = dm_table_get_num_targets(table);
+
+	if (dm_ima_alloc_and_copy_device_data(table->md, &device_data_buf, num_targets, noio))
+		goto error;
+
+	tfm = crypto_alloc_shash("sha256", 0, 0);
+	if (IS_ERR(tfm))
+		goto error;
+
+	shash->tfm = tfm;
+	digest_size = crypto_shash_digestsize(tfm);
+	digest = dm_ima_alloc(digest_size, GFP_KERNEL, noio);
+	if (!digest)
+		goto error;
+
+	r = crypto_shash_init(shash);
+	if (r)
+		goto error;
+
+	device_data_buf_len = strlen(device_data_buf);
+	memcpy(ima_buf + l, device_data_buf, device_data_buf_len);
+	l += device_data_buf_len;
+
+	for (i = 0; i < num_targets; i++) {
+		struct dm_target *ti = dm_table_get_target(table, i);
+
+		if (!ti)
+			goto error;
+
+		last_target_measured = 0;
+
+		/*
+		 * First retrieve the target metadata.
+		 */
+		scnprintf(target_metadata_buf, DM_IMA_TARGET_METADATA_BUF_LEN,
+			  "target_index=%d,target_begin=%llu,target_len=%llu,",
+			  i, ti->begin, ti->len);
+		target_metadata_buf_len = strlen(target_metadata_buf);
+
+		/*
+		 * Then retrieve the actual target data.
+		 */
+		if (ti->type->status)
+			ti->type->status(ti, type, status_flags, target_data_buf,
+					 DM_IMA_TARGET_DATA_BUF_LEN);
+		else
+			target_data_buf[0] = '\0';
+
+		target_data_buf_len = strlen(target_data_buf);
+
+		/*
+		 * Check if the total data can fit into the IMA buffer.
+		 */
+		cur_total_buf_len = l + target_metadata_buf_len + target_data_buf_len;
+
+		/*
+		 * IMA measurements for DM targets are best-effort.
+		 * If the total data buffered so far, including the current target,
+		 * is too large to fit into DM_IMA_MEASUREMENT_BUF_LEN, measure what
+		 * we have in the current buffer, and continue measuring the remaining
+		 * targets by prefixing the device metadata again.
+		 */
+		if (unlikely(cur_total_buf_len >= DM_IMA_MEASUREMENT_BUF_LEN)) {
+			dm_ima_measure_data("table_load", ima_buf, l, noio);
+			r = crypto_shash_update(shash, (const u8 *)ima_buf, l);
+			if (r < 0)
+				goto error;
+
+			memset(ima_buf, 0, DM_IMA_MEASUREMENT_BUF_LEN);
+			l = 0;
+
+			/*
+			 * Each new "table_load" entry in IMA log should have device data
+			 * prefix, so that multiple records from the same table_load for
+			 * a given device can be linked together.
+			 */
+			memcpy(ima_buf + l, device_data_buf, device_data_buf_len);
+			l += device_data_buf_len;
+
+			/*
+			 * If this iteration of the for loop turns out to be the last target
+			 * in the table, dm_ima_measure_data("table_load", ...) doesn't need
+			 * to be called again, just the hash needs to be finalized.
+			 * "last_target_measured" tracks this state.
+			 */
+			last_target_measured = 1;
+		}
+
+		/*
+		 * Fill-in all the target metadata, so that multiple targets for the same
+		 * device can be linked together.
+		 */
+		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);
+		l += target_data_buf_len;
+	}
+
+	if (!last_target_measured) {
+		dm_ima_measure_data("table_load", ima_buf, l, noio);
+
+		r = crypto_shash_update(shash, (const u8 *)ima_buf, l);
+		if (r < 0)
+			goto error;
+	}
+
+	/*
+	 * Finalize the table hash, and store it in table->md->ima.inactive_table.hash,
+	 * so that the table data can be verified against the future device state change
+	 * events, e.g. resume, rename, remove, table-clear etc.
+	 */
+	r = crypto_shash_final(shash, digest);
+	if (r < 0)
+		goto error;
+
+	digest_buf = dm_ima_alloc((digest_size*2)+1, GFP_KERNEL, noio);
+	if (!digest_buf)
+		goto error;
+
+	for (i = 0; i < digest_size; i++)
+		snprintf((digest_buf+(i*2)), 3, "%02x", digest[i]);
+
+	if (table->md->ima.active_table.hash != table->md->ima.inactive_table.hash)
+		kfree(table->md->ima.inactive_table.hash);
+
+	table->md->ima.inactive_table.hash = digest_buf;
+	table->md->ima.inactive_table.hash_len = strlen(digest_buf);
+	table->md->ima.inactive_table.num_targets = num_targets;
+
+	if (table->md->ima.active_table.device_metadata !=
+	    table->md->ima.inactive_table.device_metadata)
+		kfree(table->md->ima.inactive_table.device_metadata);
+
+	table->md->ima.inactive_table.device_metadata = device_data_buf;
+	table->md->ima.inactive_table.device_metadata_len = device_data_buf_len;
+
+	goto exit;
+error:
+	kfree(digest_buf);
+	kfree(device_data_buf);
+exit:
+	kfree(digest);
+	if (tfm)
+		crypto_free_shash(tfm);
+	kfree(ima_buf);
+	kfree(target_metadata_buf);
+	kfree(target_data_buf);
+}