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Verify best signature algorithms of all signers

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The previous implementation does not verify signature algorithms of all
signers.  It's possible that the attacker can take an old apk (with
digest and signature of old algorithm) and add their own signer block
with new/P digest and signature.  In this case, the old implementation
only verifies the attacker's signature, thus the attacker can change apk
content easily.

The solution here is to verify digests of all best signature algorithms
by all signers.

It is expected to increase verification time, if the apk does have
multiple signers with different type of digests.

Test: apks still install
Bug: 78359754
Change-Id: I607edf219c25a2a7adfa27a21a94e9bfefbb6cec
This commit is contained in:
Victor Hsieh
2018-04-20 15:45:37 -07:00
parent 4cdf6e58ed
commit 2f2ced93e3
1 changed files with 15 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

23
core/java/android/util/apk/ApkSigningBlockUtils.java
View File

@@ -92,6 +92,8 @@ final class ApkSigningBlockUtils {
throw new SecurityException("No digests provided");
}
boolean neverVerified = true;
Map<Integer, byte[]> expected1MbChunkDigests = new ArrayMap<>();
if (expectedDigests.containsKey(CONTENT_DIGEST_CHUNKED_SHA256)) {
expected1MbChunkDigests.put(CONTENT_DIGEST_CHUNKED_SHA256,
@@ -101,18 +103,23 @@ final class ApkSigningBlockUtils {
expected1MbChunkDigests.put(CONTENT_DIGEST_CHUNKED_SHA512,
expectedDigests.get(CONTENT_DIGEST_CHUNKED_SHA512));
}
if (!expected1MbChunkDigests.isEmpty()) {
try {
verifyIntegrityFor1MbChunkBasedAlgorithm(expected1MbChunkDigests, apk.getFD(),
signatureInfo);
neverVerified = false;
} catch (IOException e) {
throw new SecurityException("Cannot get FD", e);
}
}
if (expectedDigests.containsKey(CONTENT_DIGEST_VERITY_CHUNKED_SHA256)) {
verifyIntegrityForVerityBasedAlgorithm(
expectedDigests.get(CONTENT_DIGEST_VERITY_CHUNKED_SHA256), apk, signatureInfo);
} else if (!expected1MbChunkDigests.isEmpty()) {
try {
verifyIntegrityFor1MbChunkBasedAlgorithm(expected1MbChunkDigests, apk.getFD(),
signatureInfo);
} catch (IOException e) {
throw new SecurityException("Cannot get FD", e);
}
} else {
neverVerified = false;
}
if (neverVerified) {
throw new SecurityException("No known digest exists for integrity check");
}
}