Limit max number of changes pushed in a batch.

'receive.maxBatchChanges' is the maximum number of changes that
Gerrit allows to be pushed in a batch for review. When it is
exceeded Gerrit rejects the push with an error message.

This setting can be used to prevent users from uploading large
number of changes by mistake, e.g. when pushing deliveries from
external git repositories.

Default is zero, no limit.

Change-Id: Ib9821190d3c88ac9a2efbb552e21c257165a9443

Documentation/config-gerrit.txt

@@ -2602,6 +2602,17 @@ Default is zero.
 +
 Common unit suffixes of 'k', 'm', or 'g' are supported.
 
+[[receive.maxBatchChanges]]receive.maxBatchChanges::
++
+The maximum number of changes that Gerrit allows to be pushed
+in a batch for review. When this number is exceeded Gerrit rejects
+the push with an error message.
+
+This setting can be used to prevent users from uploading large
+number of changes for review by mistake.
+
+Default is zero, no limit.
+
 [[receive.threadPoolSize]]receive.threadPoolSize::
 +
 Maximum size of the thread pool in which the change data in received packs is

gerrit-server/src/main/java/com/google/gerrit/server/git/ReceiveCommits.java

@@ -1444,6 +1444,7 @@ public class ReceiveCommits {
 
       List<ChangeLookup> pending = Lists.newArrayList();
       final Set<Change.Key> newChangeIds = new HashSet<>();
+      final int maxBatchChanges = receiveConfig.maxBatchChanges;
       for (;;) {
         final RevCommit c = walk.next();
         if (c == null) {
@@ -1477,6 +1478,12 @@ public class ReceiveCommits {
 
         changeKey = new Change.Key(idStr);
         pending.add(new ChangeLookup(c, changeKey));
+        if (maxBatchChanges != 0 && pending.size() > maxBatchChanges) {
+          reject(magicBranch.cmd,
+              "the number of pushed changes in a batch exceeds the max limit "
+                  + maxBatchChanges);
+          return Collections.emptyList();
+        }
       }
 
       for (ChangeLookup p : pending) {

gerrit-server/src/main/java/com/google/gerrit/server/git/ReceiveConfig.java

@@ -25,6 +25,7 @@ class ReceiveConfig {
   final boolean checkMagicRefs;
   final boolean checkReferencedObjectsAreReachable;
   final boolean allowDrafts;
+  final int maxBatchChanges;
 
   @Inject
   ReceiveConfig(@GerritServerConfig Config config) {
@@ -37,5 +38,6 @@ class ReceiveConfig {
     allowDrafts = config.getBoolean(
         "change", null, "allowDrafts",
         true);
+    maxBatchChanges = config.getInt("receive", "maxBatchChanges", 0);
   }
 }