File URLs: Only apply MIME sniffing after resolving symbolic links.

Bug: 1035887
Change-Id: If99ff578ad31f6dbd180041fe8b1b0623ef26569
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033571Reviewed-by: Asanka Herath <asanka@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737941}

content/browser/loader/file_url_loader_factory.cc

@@ -523,9 +523,11 @@ class FileURLLoader : public network::mojom::URLLoader {
       return;
     }
 
+    // Full file path with all symbolic links resolved.
+    base::FilePath full_path = base::MakeAbsoluteFilePath(path);
     if (file_access_policy == FileAccessPolicy::kRestricted &&
-        !GetContentClient()->browser()->IsFileAccessAllowed(
-            path, base::MakeAbsoluteFilePath(path), profile_path)) {
+        !GetContentClient()->browser()->IsFileAccessAllowed(path, full_path,
+                                                            profile_path)) {
       OnClientComplete(net::ERR_ACCESS_DENIED, std::move(observer));
       return;
     }
@@ -669,9 +671,9 @@ class FileURLLoader : public network::mojom::URLLoader {
 
     // TODO(crbug.com/995177): Update mime_util.cc when WebBundles feature is
     // launched and stop using GetWebBundleFileMimeTypeFromFile().
-    if (!web_bundle_utils::GetWebBundleFileMimeTypeFromFile(path,
+    if (!web_bundle_utils::GetWebBundleFileMimeTypeFromFile(full_path,
                                                             &head->mime_type) &&
-        !net::GetMimeTypeFromFile(path, &head->mime_type)) {
+        !net::GetMimeTypeFromFile(full_path, &head->mime_type)) {
       std::string new_type;
       net::SniffMimeType(
           initial_read_buffer.data(), read_result.bytes_read, request.url,

content/browser/loader/file_url_loader_factory_browsertest.cc

@@ -178,9 +178,9 @@ IN_PROC_BROWSER_TEST_F(FileURLLoaderFactoryBrowserTest, SymlinksToFiles) {
   // Get an absolute path since |temp_dir| can contain a symbolic link.
   base::FilePath absolute_temp_dir = AbsoluteFilePath(temp_dir.GetPath());
 
-  // MIME sniffing uses the symbolic link's path, so this needs to end in
-  // ".html" for it to be sniffed as HTML.
-  base::FilePath sym_link = absolute_temp_dir.AppendASCII("link.html");
+  // MIME sniffing should use the symbolic link's destination path, so despite
+  // not having a file extension of "html", this should be rendered as HTML.
+  base::FilePath sym_link = absolute_temp_dir.AppendASCII("link.bin");
   ASSERT_TRUE(
       base::CreateSymbolicLink(AbsoluteFilePath(TestFilePath()), sym_link));