(Re-)introduce AncestorThrottle to handle 'X-Frame-Options'.

content/browser/frame_host/ancestor_throttle.cc

+// Copyright 2016 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 "content/browser/frame_host/ancestor_throttle.h"
+
+#include "base/metrics/histogram_macros.h"
+#include "base/strings/string_split.h"
+#include "base/strings/string_util.h"
+#include "base/strings/stringprintf.h"
+#include "content/browser/frame_host/frame_tree.h"
+#include "content/browser/frame_host/frame_tree_node.h"
+#include "content/browser/frame_host/navigation_handle_impl.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/navigation_handle.h"
+#include "content/public/browser/navigation_throttle.h"
+#include "content/public/common/console_message_level.h"
+#include "net/http/http_response_headers.h"
+#include "url/origin.h"
+
+namespace content {
+
+const char kXFrameOptionsSameOriginHistogram[] =
+    "Security.XFrameOptions.SameOrigin";
+
+// static
+std::unique_ptr<NavigationThrottle> AncestorThrottle::MaybeCreateThrottleFor(
+    NavigationHandle* handle) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+
+  if (handle->IsInMainFrame())
+    return nullptr;
+
+  return std::unique_ptr<NavigationThrottle>(new AncestorThrottle(handle));
+}
+
+AncestorThrottle::~AncestorThrottle() {}
+
+NavigationThrottle::ThrottleCheckResult
+AncestorThrottle::WillProcessResponse() {
+  DCHECK(!navigation_handle()->IsInMainFrame());
+
+  NavigationHandleImpl* handle =
+      static_cast<NavigationHandleImpl*>(navigation_handle());
+
+  std::string header_value;
+  HeaderDisposition disposition =
+      ParseHeader(handle->GetResponseHeaders(), &header_value);
+
+  if (disposition != HeaderDisposition::NONE)
+    UMA_HISTOGRAM_ENUMERATION(kXFrameOptionsSameOriginHistogram, TOTAL,

[clamy, 2016/12/16 15:21:43]

I find the value TOTAL a bit weird here. My suggestion would be to scrap it in
favor of having a value recorded for each of the cases below. This would mean
adding values for CONFLICT, INVALID, DENY, BYPASS & ALLOWALL (& maybe none?).

[arthursonzogni, 2016/12/19 12:01:18]

Done.

+                              XFRAMEOPTIONS_SAMEORIGIN_COUNT);
+  switch (disposition) {
+    case HeaderDisposition::CONFLICT:
+      ParseError(header_value, disposition);
+      return NavigationThrottle::BLOCK_RESPONSE;
+
+    case HeaderDisposition::INVALID:
+      ParseError(header_value, disposition);
+      // TODO(mkwst): Consider failing here.
+      return NavigationThrottle::PROCEED;
+
+    case HeaderDisposition::DENY:
+      ConsoleError(disposition);
+      return NavigationThrottle::BLOCK_RESPONSE;
+
+    case HeaderDisposition::SAMEORIGIN: {
+      UMA_HISTOGRAM_ENUMERATION(kXFrameOptionsSameOriginHistogram, SAME_ORIGIN,
+                                XFRAMEOPTIONS_SAMEORIGIN_COUNT);
+      url::Origin current_origin(navigation_handle()->GetURL());
+      url::Origin top_origin =
+          handle->frame_tree_node()->frame_tree()->root()->current_origin();
+
+      // Block the request when the top-frame has not the same origin.
+      if (!top_origin.IsSameOriginWith(current_origin)) {
+        UMA_HISTOGRAM_ENUMERATION(kXFrameOptionsSameOriginHistogram,
+                                  SAME_ORIGIN_BLOCKED,
+                                  XFRAMEOPTIONS_SAMEORIGIN_COUNT);
+        ConsoleError(disposition);
+        return NavigationThrottle::BLOCK_RESPONSE;
+      }
+
+      // Do not block the request when one of the ancestor has not the same
+      // origin, but count how many times it happens for statistics.
+      FrameTreeNode* parent = handle->frame_tree_node()->parent();
+      while (parent) {
+        if (!parent->current_origin().IsSameOriginWith(current_origin)) {
+          UMA_HISTOGRAM_ENUMERATION(kXFrameOptionsSameOriginHistogram,

[clamy, 2016/12/16 15:21:43]

I find it very weird that we're registering this value multiple times. I would
find it more understandable if we registered it in the following way:
- if the parent chain is good: SAME_ORIGIN
- if the top level is wrong and we block: SAME_ORIGIN_BLOCKED
- if the top level is good but the parent chain is wrong:
SAME_ORIGIN_WITH_BAD_ANCESTOR_CHAIN

Ideally: we would always register precisely one value for the histogram when
going in the function. This would make it easier to read and use.

[arthursonzogni, 2016/12/19 12:01:18]

Done.

+                                    SAME_ORIGIN_WITH_BAD_ANCESTOR_CHAIN,
+                                    XFRAMEOPTIONS_SAMEORIGIN_COUNT);
+          break;
+        }
+        parent = parent->parent();
+      }
+
+      return NavigationThrottle::PROCEED;
+    }
+
+    case HeaderDisposition::NONE:
+    case HeaderDisposition::BYPASS:
+    case HeaderDisposition::ALLOWALL:
+      return NavigationThrottle::PROCEED;
+  }
+  NOTREACHED();
+  return NavigationThrottle::BLOCK_RESPONSE;
+}
+
+AncestorThrottle::AncestorThrottle(NavigationHandle* handle)
+    : NavigationThrottle(handle) {}
+
+void AncestorThrottle::ParseError(const std::string& value,
+                                  HeaderDisposition disposition) {
+  DCHECK(disposition == HeaderDisposition::CONFLICT ||
+         disposition == HeaderDisposition::INVALID);
+
+  std::string message;
+  if (disposition == HeaderDisposition::CONFLICT) {
+    message = base::StringPrintf(
+        "Refused to display '%s' in a frame because it set multiple "
+        "'X-Frame-Options' headers with conflicting values "
+        "('%s'). Falling back to 'deny'.",
+        navigation_handle()->GetURL().spec().c_str(), value.c_str());
+  } else {
+    message = base::StringPrintf(
+        "Invalid 'X-Frame-Options' header encountered when loading '%s': "
+        "'%s' is not a recognized directive. The header will be ignored.",
+        navigation_handle()->GetURL().spec().c_str(), value.c_str());
+  }
+
+  // Log a console error in the parent of the current RenderFrameHost (as
+  // the current RenderFrameHost itself doesn't yet have a document).
+  navigation_handle()->GetRenderFrameHost()->GetParent()->AddMessageToConsole(
+      CONSOLE_MESSAGE_LEVEL_ERROR, message);
+}
+
+void AncestorThrottle::ConsoleError(HeaderDisposition disposition) {
+  DCHECK(disposition == HeaderDisposition::DENY ||
+         disposition == HeaderDisposition::SAMEORIGIN);
+  std::string message = base::StringPrintf(
+      "Refused to display '%s' in a frame because it set 'X-Frame-Options' "
+      "to '%s'.",
+      navigation_handle()->GetURL().spec().c_str(),
+      disposition == HeaderDisposition::DENY ? "deny" : "sameorigin");
+
+  // Log a console error in the parent of the current RenderFrameHost (as
+  // the current RenderFrameHost itself doesn't yet have a document).
+  navigation_handle()->GetRenderFrameHost()->GetParent()->AddMessageToConsole(
+      CONSOLE_MESSAGE_LEVEL_ERROR, message);
+}
+
+AncestorThrottle::HeaderDisposition AncestorThrottle::ParseHeader(
+    const net::HttpResponseHeaders* headers,
+    std::string* header_value) {
+  DCHECK(header_value);
+  if (!headers)
+    return HeaderDisposition::NONE;
+
+  // Process the 'X-Frame-Options header as per Section 2 of RFC7034:
+  // https://tools.ietf.org/html/rfc7034#section-2
+  //
+  // Note that we do not support the 'ALLOW-FROM' value, and we special-case
+  // the invalid "ALLOWALL" value due to its prevalance in the wild.
+  HeaderDisposition result = HeaderDisposition::NONE;
+  size_t iter = 0;
+  std::string value;
+  while (headers->EnumerateHeader(&iter, "x-frame-options", &value)) {
+    HeaderDisposition current = HeaderDisposition::INVALID;
+
+    base::StringPiece trimmed =
+        base::TrimWhitespaceASCII(value, base::TRIM_ALL);
+    if (!header_value->empty())
+      header_value->append(", ");
+    header_value->append(trimmed.as_string());
+
+    if (base::LowerCaseEqualsASCII(trimmed, "deny"))
+      current = HeaderDisposition::DENY;
+    else if (base::LowerCaseEqualsASCII(trimmed, "allowall"))
+      current = HeaderDisposition::ALLOWALL;
+    else if (base::LowerCaseEqualsASCII(trimmed, "sameorigin"))
+      current = HeaderDisposition::SAMEORIGIN;
+    else
+      current = HeaderDisposition::INVALID;
+
+    if (result == HeaderDisposition::NONE)
+      result = current;
+    else if (result != current)
+      result = HeaderDisposition::CONFLICT;
+  }
+
+  // If 'X-Frame-Options' would potentially block the response, check whether
+  // the 'frame-ancestors' CSP directive should take effect instead. See
+  // https://www.w3.org/TR/CSP/#frame-ancestors-and-frame-options
+  if (result != HeaderDisposition::NONE &&
+      result != HeaderDisposition::ALLOWALL) {
+    iter = 0;
+    value = std::string();
+    while (headers->EnumerateHeader(&iter, "content-security-policy", &value)) {
+      // TODO(mkwst): 'frame-ancestors' is currently handled in Blink. We should
+      // handle it here instead. Until then, don't block the request, and let
+      // Blink handle it. https://crbug.com/555418
+      std::vector<std::string> tokens = base::SplitString(
+          value, ";", base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
+      if (std::count_if(tokens.begin(), tokens.end(), [](std::string token) {
+            // The trailing " " is intentional; we'd otherwise match
+            // "frame-ancestors-is-not-this-directive".
+            return base::StartsWith(token, "frame-ancestors ",
+                                    base::CompareCase::INSENSITIVE_ASCII);
+          })) {
+        return HeaderDisposition::BYPASS;
+      }
+    }
+  }
+  return result;
+}
+
+}  // namespace content