Allow LFS-over-SSH created auth pass through ContainerAuthFilter

Issue:
When LFS operation is initiated through the SSH LFS client receives auth
token and uses it to perform requested operation e.g.:

  POST /gerrit/test-org/test-no-block/info/lfs/objects/batch
  Authorization: Ssh: ...
  Content-Type: application/vnd.git-lfs+json; charset=utf-8
  {
    "operation":"upload","objects"...
  }

ContainerAuthFilter searches for existing user but none of the
containers can perform successful LFS auth (as it is deeply buried in
the plugin internals) therefore typically it is configured to let it go
through to eventually fail in the filter with:

  403 Forbidden

Solution:
Modify ContainerAuthFilter so that it returns 'true' when Content-Type
indicates LFS request is against LFS and Authorization header value
starts with "Ssh: " string (similarly to ProjectBasicAuthFilter when
it doesn't start with "Basic ").

Rationale:
ContainerAuthFilter is installed for requests that either go through
/a/* (authorised path) or to LFS (note that LFS over HTTP sends
auth token even when request is not `/a/` prefixed - hence user
can be obtained from request with the first call without sending
401 back and re-sending request with `/a/` prefix.
In terms of LFS over SSH it is again request against LFS but in this
case it has `Ssh: ` based auth token that is not recognized by
filter and results in 403.

This change is safe as it introduces exception only for LFS requests
that rely on internal LFS auth anyway.

Change-Id: Ia886dc284c8ded9c21a5b9f57628f228c1e691f0
Signed-off-by: Jacek Centkowski <jcentkowski@collab.net>

2 files changed, 21 insertions, 1 deletions

diff --git a/gerrit-httpd/src/main/java/com/google/gerrit/httpd/ContainerAuthFilter.java b/gerrit-httpd/src/main/java/com/google/gerrit/httpd/ContainerAuthFilter.java
index 07893ba7ea..7d261c8f17 100644
--- a/gerrit-httpd/src/main/java/com/google/gerrit/httpd/ContainerAuthFilter.java
+++ b/gerrit-httpd/src/main/java/com/google/gerrit/httpd/ContainerAuthFilter.java
@@ -17,9 +17,12 @@ package com.google.gerrit.httpd;
 import static com.google.common.base.MoreObjects.firstNonNull;
 import static com.google.common.base.Strings.emptyToNull;
 import static com.google.common.net.HttpHeaders.AUTHORIZATION;
+import static com.google.gerrit.extensions.api.lfs.LfsDefinitions.CONTENTTYPE_VND_GIT_LFS_JSON;
+import static com.google.gerrit.httpd.GerritAuthModule.NOT_AUTHORIZED_LFS_URL_REGEX;
 import static javax.servlet.http.HttpServletResponse.SC_FORBIDDEN;
 import static javax.servlet.http.HttpServletResponse.SC_UNAUTHORIZED;
 
+import com.google.common.base.Strings;
 import com.google.gerrit.extensions.registration.DynamicItem;
 import com.google.gerrit.httpd.restapi.RestApiServlet;
 import com.google.gerrit.server.AccessPath;
@@ -31,6 +34,7 @@ import com.google.inject.Inject;
 import com.google.inject.Singleton;
 import java.io.IOException;
 import java.util.Locale;
+import java.util.regex.Pattern;
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
@@ -54,6 +58,9 @@ import org.eclipse.jgit.lib.Config;
  */
 @Singleton
 class ContainerAuthFilter implements Filter {
+  private static final String LFS_AUTH_PREFIX = "Ssh: ";
+  private static final Pattern LFS_ENDPOINT = Pattern.compile(NOT_AUTHORIZED_LFS_URL_REGEX);
+
   private final DynamicItem<WebSession> session;
   private final AccountCache accountCache;
   private final Config config;
@@ -92,6 +99,11 @@ class ContainerAuthFilter implements Filter {
   private boolean verify(HttpServletRequest req, HttpServletResponse rsp) throws IOException {
     String username = RemoteUserUtil.getRemoteUser(req, loginHttpHeader);
     if (username == null) {
+      if (isLfsOverSshRequest(req)) {
+        // LFS-over-SSH auth request cannot be authorized by container
+        // therefore let it go through the filter
+        return true;
+      }
       rsp.sendError(SC_FORBIDDEN);
       return false;
     }
@@ -109,4 +121,12 @@ class ContainerAuthFilter implements Filter {
     ws.setAccessPathOk(AccessPath.REST_API, true);
     return true;
   }
+
+  private static boolean isLfsOverSshRequest(HttpServletRequest req) {
+    String hdr = req.getHeader(AUTHORIZATION);
+    return CONTENTTYPE_VND_GIT_LFS_JSON.equals(req.getContentType())
+        && !Strings.isNullOrEmpty(hdr)
+        && hdr.startsWith(LFS_AUTH_PREFIX)
+        && LFS_ENDPOINT.matcher(req.getRequestURI()).matches();
+  }
 }
diff --git a/gerrit-httpd/src/main/java/com/google/gerrit/httpd/GerritAuthModule.java b/gerrit-httpd/src/main/java/com/google/gerrit/httpd/GerritAuthModule.java
index c0ef207194..253c220774 100644
--- a/gerrit-httpd/src/main/java/com/google/gerrit/httpd/GerritAuthModule.java
+++ b/gerrit-httpd/src/main/java/com/google/gerrit/httpd/GerritAuthModule.java
@@ -24,7 +24,7 @@ import javax.servlet.Filter;
 
 /** Configures filter for authenticating REST requests. */
 public class GerritAuthModule extends ServletModule {
-  private static final String NOT_AUTHORIZED_LFS_URL_REGEX = "^(?:(?!/a/))" + LFS_URL_WO_AUTH_REGEX;
+  static final String NOT_AUTHORIZED_LFS_URL_REGEX = "^(?:(?!/a/))" + LFS_URL_WO_AUTH_REGEX;
   private final AuthConfig authConfig;
 
   @Inject