KEYS: asym_tpm: extract key size & public key [ver #2]

The parsed BER/DER blob obtained from user space contains a TPM_Key
structure.  This structure has some information about the key as well as
the public key portion.

This patch extracts this information for future use.

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: James Morris <james.morris@microsoft.com>

1 files changed, 112 insertions, 0 deletions

diff --git a/crypto/asymmetric_keys/asym_tpm.c b/crypto/asymmetric_keys/asym_tpm.c
index d0b2b97e8e54..308c51e055a4 100644
--- a/crypto/asymmetric_keys/asym_tpm.c
+++ b/crypto/asymmetric_keys/asym_tpm.c
@@ -7,6 +7,7 @@
 #include <linux/seq_file.h>
 #include <linux/scatterlist.h>
 #include <linux/tpm.h>
+#include <asm/unaligned.h>
 #include <keys/asymmetric-subtype.h>
 #include <crypto/asym_tpm_subtype.h>
 
@@ -37,6 +38,110 @@ static void asym_tpm_destroy(void *payload0, void *payload3)
         kfree(tk);
 }
 
+/*
+ * Parse enough information out of TPM_KEY structure:
+ * TPM_STRUCT_VER -> 4 bytes
+ * TPM_KEY_USAGE -> 2 bytes
+ * TPM_KEY_FLAGS -> 4 bytes
+ * TPM_AUTH_DATA_USAGE -> 1 byte
+ * TPM_KEY_PARMS -> variable
+ * UINT32 PCRInfoSize -> 4 bytes
+ * BYTE* -> PCRInfoSize bytes
+ * TPM_STORE_PUBKEY
+ * UINT32 encDataSize;
+ * BYTE* -> encDataSize;
+ *
+ * TPM_KEY_PARMS:
+ * TPM_ALGORITHM_ID -> 4 bytes
+ * TPM_ENC_SCHEME -> 2 bytes
+ * TPM_SIG_SCHEME -> 2 bytes
+ * UINT32 parmSize -> 4 bytes
+ * BYTE* -> variable
+ */
+static int extract_key_parameters(struct tpm_key *tk)
+{
+        const void *cur = tk->blob;
+        uint32_t len = tk->blob_len;
+        const void *pub_key;
+        uint32_t sz;
+        uint32_t key_len;
+
+        if (len < 11)
+                return -EBADMSG;
+
+        /* Ensure this is a legacy key */
+        if (get_unaligned_be16(cur + 4) != 0x0015)
+                return -EBADMSG;
+
+        /* Skip to TPM_KEY_PARMS */
+        cur += 11;
+        len -= 11;
+
+        if (len < 12)
+                return -EBADMSG;
+
+        /* Make sure this is an RSA key */
+        if (get_unaligned_be32(cur) != 0x00000001)
+                return -EBADMSG;
+
+        /* Make sure this is TPM_ES_RSAESPKCSv15 encoding scheme */
+        if (get_unaligned_be16(cur + 4) != 0x0002)
+                return -EBADMSG;
+
+        /* Make sure this is TPM_SS_RSASSAPKCS1v15_DER signature scheme */
+        if (get_unaligned_be16(cur + 6) != 0x0003)
+                return -EBADMSG;
+
+        sz = get_unaligned_be32(cur + 8);
+        if (len < sz + 12)
+                return -EBADMSG;
+
+        /* Move to TPM_RSA_KEY_PARMS */
+        len -= 12;
+        cur += 12;
+
+        /* Grab the RSA key length */
+        key_len = get_unaligned_be32(cur);
+
+        switch (key_len) {
+        case 512:
+        case 1024:
+        case 1536:
+        case 2048:
+                break;
+        default:
+                return -EINVAL;
+        }
+
+        /* Move just past TPM_KEY_PARMS */
+        cur += sz;
+        len -= sz;
+
+        if (len < 4)
+                return -EBADMSG;
+
+        sz = get_unaligned_be32(cur);
+        if (len < 4 + sz)
+                return -EBADMSG;
+
+        /* Move to TPM_STORE_PUBKEY */
+        cur += 4 + sz;
+        len -= 4 + sz;
+
+        /* Grab the size of the public key, it should jive with the key size */
+        sz = get_unaligned_be32(cur);
+        if (sz > 256)
+                return -EINVAL;
+
+        pub_key = cur + 4;
+
+        tk->key_len = key_len;
+        tk->pub_key = pub_key;
+        tk->pub_key_len = sz;
+
+        return 0;
+}
+
 /* Given the blob, parse it and load it into the TPM */
 struct tpm_key *tpm_key_create(const void *blob, uint32_t blob_len)
 {
@@ -64,8 +169,15 @@ struct tpm_key *tpm_key_create(const void *blob, uint32_t blob_len)
 
         tk->blob_len = blob_len;
 
+        r = extract_key_parameters(tk);
+        if (r < 0)
+                goto error_extract;
+
         return tk;
 
+error_extract:
+        kfree(tk->blob);
+        tk->blob_len = 0;
 error_memdup:
         kfree(tk);
 error: