Validate decryption key length to decrypt function.

Cherry picked from http://go/ag/3038278.

AesCtrDecryptor::decrypt() doesn't check whether the size of "key"
is equal to 16 bytes,  which may lead to an OOB read problem in the
context of mediadrmserver.

Add DecryptsWithEmptyKey and DecryptsWithKeyTooLong unit tests.

Test: ClearKeyDrmUnitTest
  adb shell LD_LIBRARY_PATH="/vendor/lib/mediadrm"
  /data/nativetest/ClearKeyDrmUnitTest/ClearKeyDrmUnitTest

bug: 63982768
Change-Id: I1f22c9df2b051972b2c532608b7f203e3ce77926

drm/mediadrm/plugins/clearkey/AesCtrDecryptor.cpp

@@ -36,6 +36,11 @@ android::status_t AesCtrDecryptor::decrypt(const android::Vector<uint8_t>& key,
     uint8_t previousEncryptedCounter[kBlockSize];
     memset(previousEncryptedCounter, 0, kBlockSize);
 
+    if (key.size() != kBlockSize || (sizeof(Iv) / sizeof(uint8_t)) != kBlockSize) {
+        android_errorWriteLog(0x534e4554, "63982768");
+        return android::ERROR_DRM_DECRYPT;
+    }
+
     size_t offset = 0;
     AES_KEY opensslKey;
     AES_set_encrypt_key(key.array(), kBlockBitCount, &opensslKey);

drm/mediadrm/plugins/clearkey/AesCtrDecryptor.h

@@ -18,6 +18,7 @@
 #define CLEARKEY_AES_CTR_DECRYPTOR_H_
 
 #include <media/stagefright/foundation/ABase.h>
+#include <media/stagefright/MediaErrors.h>
 #include <Utils.h>
 #include <utils/Errors.h>
 #include <utils/Vector.h>

drm/mediadrm/plugins/clearkey/tests/AesCtrDecryptorUnittest.cpp

@@ -34,7 +34,7 @@ class AesCtrDecryptorTest : public ::testing::Test {
                             uint8_t* destination, const SubSample* subSamples,
                             size_t numSubSamples, size_t* bytesDecryptedOut) {
         Vector<uint8_t> keyVector;
-        keyVector.appendArray(key, kBlockSize);
+        keyVector.appendArray(key, sizeof(key) / sizeof(uint8_t));
 
         AesCtrDecryptor decryptor;
         return decryptor.decrypt(keyVector, iv, source, destination, subSamples,
@@ -57,6 +57,67 @@ class AesCtrDecryptorTest : public ::testing::Test {
     }
 };
 
+TEST_F(AesCtrDecryptorTest, DecryptsWithEmptyKey) {
+    const size_t kTotalSize = 64;
+    const size_t kNumSubsamples = 1;
+
+    // Test vectors from NIST-800-38A
+    Iv iv = {
+        0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+        0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
+    };
+
+    uint8_t source[kTotalSize] = { 0 };
+    uint8_t destination[kTotalSize] = { 0 };
+    SubSample subSamples[kNumSubsamples] = {
+        {0, 64}
+    };
+
+    size_t bytesDecrypted = 0;
+    Vector<uint8_t> keyVector;
+    keyVector.clear();
+
+    AesCtrDecryptor decryptor;
+    ASSERT_EQ(android::ERROR_DRM_DECRYPT, decryptor.decrypt(keyVector, iv,
+              &source[0], &destination[0],
+              &subSamples[0], kNumSubsamples, &bytesDecrypted));
+    ASSERT_EQ(0u, bytesDecrypted);
+}
+
+TEST_F(AesCtrDecryptorTest, DecryptsWithKeyTooLong) {
+    const size_t kTotalSize = 64;
+    const size_t kNumSubsamples = 1;
+
+    // Test vectors from NIST-800-38A
+    uint8_t key[kBlockSize * 2] = {
+        0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
+        0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c,
+        0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
+        0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c
+    };
+
+    Iv iv = {
+        0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+        0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
+    };
+
+    uint8_t source[kTotalSize] = { 0 };
+    uint8_t destination[kTotalSize] = { 0 };
+    SubSample subSamples[kNumSubsamples] = {
+        {0, 64}
+    };
+
+    size_t bytesDecrypted = 0;
+    Vector<uint8_t> keyVector;
+    keyVector.appendArray(key, sizeof(key) / sizeof(uint8_t));
+
+    AesCtrDecryptor decryptor;
+    ASSERT_EQ(android::ERROR_DRM_DECRYPT, decryptor.decrypt(keyVector, iv,
+              &source[0], &destination[0],
+              &subSamples[0], kNumSubsamples, &bytesDecrypted));
+    ASSERT_EQ(0u, bytesDecrypted);
+}
+
 TEST_F(AesCtrDecryptorTest, DecryptsContiguousEncryptedBlock) {
     const size_t kTotalSize = 64;
     const size_t kNumSubsamples = 1;