dm-ima: use SHA-256 library

Make dm_ima_measure_on_table_load() use the SHA-256 library API instead
of crypto_shash to calculate the SHA-256 hash value that it needs.  This
is simpler and more efficient.  It also ensures that SHA-256 is actually
available and doesn't fail due to the unreliable loading by name.

While doing this, also use kasprintf() to simplify building the string
version of the digest.

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index c58a9a8ea54e924e0522d642643900fb6a10bb1e..53351048d3ec64c6459600d362aa71547916142b 100644 (file)
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -226,6 +226,7 @@ config BLK_DEV_DM
        select BLOCK_HOLDER_DEPRECATED if SYSFS
        select BLK_DEV_DM_BUILTIN
        select BLK_MQ_STACKING
+       select CRYPTO_LIB_SHA256 if IMA
        depends on DAX || DAX=n
        help
          Device-mapper is a low level volume manager.  It works by allowing

diff --git a/drivers/md/dm-ima.c b/drivers/md/dm-ima.c
index efb3cd4f9cd453011b7cc0e78933a26718758c73..9495ca0350563f4bdf36deced60aa01487cb1f39 100644 (file)
--- a/drivers/md/dm-ima.c
+++ b/drivers/md/dm-ima.c
@@ -12,9 +12,7 @@
 
 #include <linux/ima.h>
 #include <linux/sched/mm.h>
-#include <crypto/hash.h>
-#include <linux/crypto.h>
-#include <crypto/hash_info.h>
+#include <crypto/sha2.h>
 
 #define DM_MSG_PREFIX "ima"
 
@@ -178,19 +176,13 @@ void dm_ima_measure_on_table_load(struct dm_table *table, unsigned int status_fl
        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;
+       int last_target_measured = -1;
        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;
+       struct sha256_ctx hash_ctx;
+       u8 digest[SHA256_DIGEST_SIZE];
        bool noio = false;
-       /*
-        * In below hash_alg_prefix_len assignment +1 is for the additional char (':'),
-        * when prefixing the hash value with the hash algorithm name. e.g. sha256:<hash_value>.
-        */
-       const size_t hash_alg_prefix_len = strlen(DM_IMA_TABLE_HASH_ALG) + 1;
        char table_load_event_name[] = "dm_table_load";
 
        ima_buf = dm_ima_alloc(DM_IMA_MEASUREMENT_BUF_LEN, noio);
@@ -210,19 +202,7 @@ 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(DM_IMA_TABLE_HASH_ALG, 0, 0);
-       if (IS_ERR(tfm))
-               goto error;
-
-       shash->tfm = tfm;
-       digest_size = crypto_shash_digestsize(tfm);
-       digest = dm_ima_alloc(digest_size, noio);
-       if (!digest)
-               goto error;
-
-       r = crypto_shash_init(shash);
-       if (r)
-               goto error;
+       sha256_init(&hash_ctx);
 
        memcpy(ima_buf + l, DM_IMA_VERSION_STR, table->md->ima.dm_version_str_len);
        l += table->md->ima.dm_version_str_len;
@@ -270,9 +250,7 @@ void dm_ima_measure_on_table_load(struct dm_table *table, unsigned int status_fl
                 */
                if (unlikely(cur_total_buf_len >= DM_IMA_MEASUREMENT_BUF_LEN)) {
                        dm_ima_measure_data(table_load_event_name, ima_buf, l, noio);
-                       r = crypto_shash_update(shash, (const u8 *)ima_buf, l);
-                       if (r < 0)
-                               goto error;
+                       sha256_update(&hash_ctx, (const u8 *)ima_buf, l);
 
                        memset(ima_buf, 0, DM_IMA_MEASUREMENT_BUF_LEN);
                        l = 0;
@@ -311,9 +289,7 @@ void dm_ima_measure_on_table_load(struct dm_table *table, unsigned int status_fl
        if (!last_target_measured) {
                dm_ima_measure_data(table_load_event_name, ima_buf, l, noio);
 
-               r = crypto_shash_update(shash, (const u8 *)ima_buf, l);
-               if (r < 0)
-                       goto error;
+               sha256_update(&hash_ctx, (const u8 *)ima_buf, l);
        }
 
        /*
@@ -321,20 +297,13 @@ void dm_ima_measure_on_table_load(struct dm_table *table, unsigned int status_fl
         * 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) + hash_alg_prefix_len + 1, noio);
+       sha256_final(&hash_ctx, digest);
 
+       digest_buf = kasprintf(GFP_KERNEL, "sha256:%*phN", SHA256_DIGEST_SIZE,
+                              digest);
        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 + 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);
 
@@ -354,9 +323,6 @@ 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);

diff --git a/drivers/md/dm-ima.h b/drivers/md/dm-ima.h
index 568870a1a145607738a43f11ee4d13457619d1ec..a403deca6093e3fc825a1cabb28febfb6058e1d1 100644 (file)
--- a/drivers/md/dm-ima.h
+++ b/drivers/md/dm-ima.h
@@ -15,7 +15,6 @@
 #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"
 
 #define __dm_ima_stringify(s) #s
 #define __dm_ima_str(s) __dm_ima_stringify(s)