avbtool: Make raw_sign check the length of signature.
avbtool give users the option to use their own signing tool. Without
checking the length of signature provided by tool, generated vbmeta
could be broken because of inconsistency of data. To prevent this,
guard code to check the length is added.
Bug: None
Test: All unit tests pass.
Change-Id: I77b7ebd46ddc22393c1a75dce79f2a02c116b95d
diff --git a/avbtool b/avbtool
index 2dfb259..a56a730 100755
--- a/avbtool
+++ b/avbtool
@@ -385,12 +385,14 @@
raise AvbError('Unknown algorithm type {}'.format(alg_type))
-def raw_sign(signing_helper, algorithm_name, key_path, raw_data_to_sign):
+def raw_sign(signing_helper, algorithm_name, signature_num_bytes, key_path,
+ raw_data_to_sign):
"""Computes a raw RSA signature using |signing_helper| or openssl.
Arguments:
signing_helper: Program which signs a hash and returns the signature.
algorithm_name: The algorithm name as per the ALGORITHMS dict.
+ signature_num_bytes: Number of bytes used to store the signature.
key_path: Path to the private key file. Must be PEM format.
raw_data_to_sign: Data to sign (bytearray or str expected).
@@ -417,7 +419,10 @@
retcode = p.wait()
if retcode != 0:
raise AvbError('Error signing: {}'.format(perr))
- return bytearray(pout)
+ signature = bytearray(pout)
+ if len(signature) != signature_num_bytes:
+ raise AvbError('Error signing: Invalid length of signature')
+ return signature
class ImageChunk(object):
@@ -2166,7 +2171,8 @@
# Calculate the signature.
padding_and_hash = str(bytearray(alg.padding)) + binary_hash
- binary_signature.extend(raw_sign(signing_helper, algorithm_name, key_path,
+ binary_signature.extend(raw_sign(signing_helper, algorithm_name,
+ alg.signature_num_bytes, key_path,
padding_and_hash))
# Generate Authentication data block.
@@ -2682,12 +2688,14 @@
if authority_key_path:
padding_and_hash = bytearray()
algorithm_name = 'SHA512_RSA4096'
+ alg = ALGORITHMS[algorithm_name]
hasher = hashlib.sha512()
- padding_and_hash.extend(ALGORITHMS[algorithm_name].padding)
+ padding_and_hash.extend(alg.padding)
hasher.update(signed_data)
padding_and_hash.extend(hasher.digest())
signature.extend(raw_sign(signing_helper, algorithm_name,
- authority_key_path, padding_and_hash))
+ alg.signature_num_bytes, authority_key_path,
+ padding_and_hash))
output.write(signed_data)
output.write(signature)