Implement anonymous, opt-in, collection of OS X binary integrity incidents.

chrome/browser/safe_browsing/signature_evaluator_mac.mm

+// Copyright (c) 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/safe_browsing/signature_evaluator_mac.h"
+
+#include <CoreFoundation/CoreFoundation.h>
+#include <Foundation/Foundation.h>
+#include <Security/Security.h>
+#include <sys/xattr.h>
+
+#include "base/mac/foundation_util.h"
+#include "base/mac/mac_util.h"
+#include "base/mac/scoped_cftyperef.h"
+#include "base/mac/scoped_nsobject.h"
+#include "base/strings/sys_string_conversions.h"
+#include "chrome/common/safe_browsing/binary_feature_extractor.h"
+#include "chrome/common/safe_browsing/csd.pb.h"
+#include "chrome/common/safe_browsing/mach_o_image_reader_mac.h"
+
+namespace safe_browsing {
+
+namespace {
+
+// OS X code signing data can be stored in extended attributes as well. This is
+// a list of the extended attributes slots currently used in Security.framework,
+// from codesign.h (see the kSecCS_* constants).
+const char* const xattrs[] = {
+  "com.apple.cs.CodeDirectory",
+  "com.apple.cs.CodeSignature",
+  "com.apple.cs.CodeRequirements",
+  "com.apple.cs.CodeResources",
+  "com.apple.cs.CodeApplication",
+  "com.apple.cs.CodeEntitlements",
+};
+
+// Convenience function to get the appropriate path from a variety of NSObject
+// types.
+bool GetPathFromNSObject(id obj, std::string* output) {
+  if (NSString* str = base::mac::ObjCCast<NSString>(obj)) {
+    output->assign([str UTF8String]);
+    return true;
+  } else if (NSURL* url = base::mac::ObjCCast<NSURL>(obj)) {
+    output->assign([[url path] UTF8String]);
+    return true;
+  } else if (NSBundle* bundle = base::mac::ObjCCast<NSBundle>(obj)) {
+    output->assign([[bundle bundlePath] UTF8String]);
+    return true;
+  }
+  return false;
+}
+
+}  // namespace
+
+MacSignatureEvaluator::MacSignatureEvaluator(
+    const base::FilePath& signed_object_path)
+    : path_(signed_object_path),
+      has_requirement_(false),
+      code_(nullptr),
+      requirement_(nullptr) {}
+
+MacSignatureEvaluator::MacSignatureEvaluator(
+    const base::FilePath& signed_object_path,
+    const std::string& requirement)
+    : path_(signed_object_path),
+      requirement_str_(requirement),
+      has_requirement_(true),
+      code_(nullptr),
+      requirement_(nullptr) {}
+
+MacSignatureEvaluator::~MacSignatureEvaluator() {}
+
+void MacSignatureEvaluator::ReportAlteredFiles(
+    id detail,
+    int32_t err_code,
+    std::vector<ClientIncidentReport_IncidentData_BinaryIntegrityIncident>&
+        results) {
+  if (NSArray* arr = base::mac::ObjCCast<NSArray>(detail)) {
+    for (id obj in arr)
+      ReportAlteredFiles(obj, err_code, results);
+  } else {
+    std::string path_str;
+    if (!GetPathFromNSObject(detail, &path_str))
+      return;
+
+    base::FilePath path(path_str);
+    ClientIncidentReport_IncidentData_BinaryIntegrityIncident incident;
+    incident.set_file_basename(path.BaseName().AsUTF8Unsafe());
+    incident.set_sec_error(err_code);
+    scoped_refptr<BinaryFeatureExtractor> bfe = new BinaryFeatureExtractor();
+    // TODO(kerrnel): if Chrome ever opts into the OS X "kill" semantics, this
+    // call has to change. `ExtractImageFeatures` maps the file, which will
+    // cause Chrome to be killed before it can report on the invalid file.
+    // This call will need to read(2) the binary into a buffer.
+    if (!bfe->ExtractImageFeatures(
+            path, BinaryFeatureExtractor::kDefaultOptions,
+            incident.mutable_image_headers(),
+            incident.mutable_signature()->mutable_signed_data())) {
+      // If this is not a mach-o file, search inside the extended attributes.
+      for (const char* attr : xattrs) {
+        ssize_t rc = getxattr(path.value().c_str(), attr, nullptr, 0, 0, 0);
+        if (rc >= 0) {
+          std::vector<uint8_t> xattr_data(rc);
+          if (getxattr(path.value().c_str(), attr, &xattr_data[0],
+                       xattr_data.size(), 0, 0) >= 0) {
+            ClientDownloadRequest_ExtendedAttr* xattr_msg =
+                incident.mutable_signature()->add_xattr();
+            xattr_msg->set_key(attr);
+            xattr_msg->set_value(xattr_data.data(), xattr_data.size());
+          }
+        }
+      }
+    }
+    results.push_back(incident);
+  }
+}
+
+bool MacSignatureEvaluator::Initialize() {
+  base::scoped_nsobject<NSURL> code_url([[NSURL alloc]
+      initFileURLWithPath:base::SysUTF8ToNSString(path_.value())]);
+  if (!code_url)
+    return false;
+
+  if (SecStaticCodeCreateWithPath(base::mac::NSToCFCast(code_url.get()),
+                                  kSecCSDefaultFlags,
+                                  code_.InitializeInto()) != errSecSuccess)

[Robert Sesek, 2015/10/08 19:20:06]

nit: needs braces since multi-line

[Greg K, 2015/10/09 17:12:01]

Done.

+    return false;
+
+  if (has_requirement_) {
+    if (SecRequirementCreateWithString(
+            base::mac::NSToCFCast(base::SysUTF8ToNSString(requirement_str_)),
+            kSecCSDefaultFlags, requirement_.InitializeInto()) != errSecSuccess)

[Robert Sesek, 2015/10/08 19:20:06]

nit: same, braces required

[Greg K, 2015/10/09 17:12:01]

Done.

+      return false;
+  }
+
+  return true;
+}
+
+bool MacSignatureEvaluator::PerformEvaluation(
+    std::vector<ClientIncidentReport_IncidentData_BinaryIntegrityIncident>&
+        results) {
+  base::ScopedCFTypeRef<CFErrorRef> errors(nullptr);
+  OSStatus err = SecStaticCodeCheckValidityWithErrors(
+      code_, kSecCSCheckAllArchitectures, requirement_,
+      errors.InitializeInto());
+  if (err == errSecSuccess)
+    return true;
+  // This adds the signature of the main binary to the incident reports.
+  ReportAlteredFiles(base::SysUTF8ToNSString(path_.value()), err, results);
+  if (errors) {
+    NSDictionary* info = [base::mac::CFToNSCast(errors.get()) userInfo];
+    CFStringRef keys[] = {
+        kSecCFErrorResourceAltered, kSecCFErrorResourceMissing,
+    };
+    for (CFStringRef key : keys) {
+      if (id detail = [info objectForKey:base::mac::CFToNSCast(key)])
+        ReportAlteredFiles(detail, err, results);
+    }
+  }
+  return false;
+}
+
+}  // namespace safe_browsing