From ccda4faf7b869d271b218d5297d7898fa4cf0af5 Mon Sep 17 00:00:00 2001
From: Alex Dale <sigquit@google.com>
Date: Fri, 9 Apr 2021 00:43:34 -0700
Subject: [PATCH] Cleaned up OEMCrypto security level getter.

[ Merge of http://go/wvgerrit/121566 ]

This clean up is part of a larger usage table initialization fix.

Bug: 169195093
Change-Id: I3ee818d1e5621f1f2fa64b189da4e66503d5e680
---
 .../cdm/core/src/crypto_session.cpp           | 61 +++++++++++--------
 1 file changed, 35 insertions(+), 26 deletions(-)

diff --git a/libwvdrmengine/cdm/core/src/crypto_session.cpp b/libwvdrmengine/cdm/core/src/crypto_session.cpp
index e8b9a23a..241424d9 100644
--- a/libwvdrmengine/cdm/core/src/crypto_session.cpp
+++ b/libwvdrmengine/cdm/core/src/crypto_session.cpp
@@ -490,37 +490,46 @@ CdmSecurityLevel CryptoSession::GetSecurityLevel() {
 }
 
 CdmSecurityLevel CryptoSession::GetSecurityLevel(
-    SecurityLevel requested_level) {
-  LOGV("Getting security level: requested_level = %d",
-       static_cast<int>(requested_level));
+    SecurityLevel requested_security_level) {
+  LOGV("Getting security level: requested_security_level = %d",
+       static_cast<int>(requested_security_level));
   RETURN_IF_UNINITIALIZED(kSecurityLevelUninitialized);
-
-  std::string security_level;
-  WithOecReadLock("GetSecurityLevel", [&] {
-    security_level = OEMCrypto_SecurityLevel(requested_level);
+  const char* const level = WithOecReadLock("GetSecurityLevel", [&] {
+    return OEMCrypto_SecurityLevel(requested_security_level);
   });
-
-  if ((security_level.size() != 2) || (security_level.at(0) != 'L')) {
+  if (level == nullptr) {
+    LOGE("Security level is null: requested_security_level = %d",
+         static_cast<int>(requested_security_level));
     return kSecurityLevelUnknown;
   }
-
-  CdmSecurityLevel cdm_security_level;
-  switch (security_level.at(1)) {
-    case '1':
-      cdm_security_level = kSecurityLevelL1;
-      break;
-    case '2':
-      cdm_security_level = kSecurityLevelL2;
-      break;
-    case '3':
-      cdm_security_level = kSecurityLevelL3;
-      break;
-    default:
-      cdm_security_level = kSecurityLevelUnknown;
-      break;
+  // Check length in the event of a bad pointer.
+  // |kMaxSecurityLevelLength| is a value larger than expected to
+  // be able to detect an overrun.
+  constexpr size_t kMaxSecurityLevelLength = 5;
+  const size_t length = strnlen(level, kMaxSecurityLevelLength);
+  constexpr size_t kExpectedSecurityLevelLength = 2;
+  if (length != kExpectedSecurityLevelLength) {
+    LOGE(
+        "Unexpected security level length: "
+        "length = %zu, requested_security_level = %d",
+        length, static_cast<int>(requested_security_level));
+    return kSecurityLevelUnknown;
   }
-
-  return cdm_security_level;
+  const std::string security_level(level);
+  if (security_level == "L1") {
+    return kSecurityLevelL1;
+  }
+  if (security_level == "L2") {
+    return kSecurityLevelL2;
+  }
+  if (security_level == "L3") {
+    return kSecurityLevelL3;
+  }
+  LOGE(
+      "Ill-formed security level: "
+      "level = \"%s\", requested_security_level = %d",
+      security_level.c_str(), static_cast<int>(requested_security_level));
+  return kSecurityLevelUnknown;
 }
 
 CdmResponseType CryptoSession::GetInternalDeviceUniqueId(