[dm-devel] [PATCH 1/6] dm ima: prefix dm table hashes in ima log with hash algorithm

[Tushar Sugandhi <tusharsu@linux.microsoft.com>]

The active/inactive table hashes measured in the ima log do not contain
the information about hash algorithm.  This information is useful for the
attestation servers to recreate the hashes and compare them with the ones
present in the ima log to verify the table contents.

Prefix the table hashes in various DM events in ima log with the hash
algorithm used to compute those hashes.

Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
---
 drivers/md/dm-ima.c | 15 ++++++++++++---
 drivers/md/dm-ima.h |  1 +
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-ima.c b/drivers/md/dm-ima.c
index 91ea4a7202ab..4bab35c8f0c7 100644
--- a/drivers/md/dm-ima.c
+++ b/drivers/md/dm-ima.c
@@ -186,6 +186,12 @@ void dm_ima_measure_on_table_load(struct dm_table *table, unsigned int status_fl
 	struct crypto_shash *tfm = NULL;
 	u8 *digest = NULL;
 	bool noio = false;
+	const size_t hash_alg_prefix_len = strlen(DM_IMA_TABLE_HASH_ALG) + 1;
+				/*
+				 * +1 for the additional char (':'), when prefixing
+				 * the hash value with the hash algorithm name.
+				 * e.g. sha256:<hash_value>.
+				 */
 
 	ima_buf = dm_ima_alloc(DM_IMA_MEASUREMENT_BUF_LEN, GFP_KERNEL, noio);
 	if (!ima_buf)
@@ -204,7 +210,7 @@ void dm_ima_measure_on_table_load(struct dm_table *table, unsigned int status_fl
 	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);
+	tfm = crypto_alloc_shash(DM_IMA_TABLE_HASH_ALG, 0, 0);
 	if (IS_ERR(tfm))
 		goto error;
 
@@ -315,12 +321,15 @@ void dm_ima_measure_on_table_load(struct dm_table *table, unsigned int status_fl
 	if (r < 0)
 		goto error;
 
-	digest_buf = dm_ima_alloc((digest_size*2)+1, GFP_KERNEL, noio);
+	digest_buf = dm_ima_alloc((digest_size*2) + hash_alg_prefix_len + 1, GFP_KERNEL, noio);
+
 	if (!digest_buf)
 		goto error;
 
+	snprintf(digest_buf, hash_alg_prefix_len + 1, "%s:", DM_IMA_TABLE_HASH_ALG);
+
 	for (i = 0; i < digest_size; i++)
-		snprintf((digest_buf+(i*2)), 3, "%02x", digest[i]);
+		snprintf((digest_buf + hash_alg_prefix_len + (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);
diff --git a/drivers/md/dm-ima.h b/drivers/md/dm-ima.h
index 6e6f18bf05b4..0731a51565d6 100644
--- a/drivers/md/dm-ima.h
+++ b/drivers/md/dm-ima.h
@@ -16,6 +16,7 @@
 #define DM_IMA_TARGET_METADATA_BUF_LEN	128
 #define DM_IMA_TARGET_DATA_BUF_LEN	2048
 #define DM_IMA_DEVICE_CAPACITY_BUF_LEN	128
+#define DM_IMA_TABLE_HASH_ALG		"sha256"
 
 #ifdef CONFIG_IMA
 
-- 
2.32.0


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