[CAS] Fix an off-by-one error in CAS validation

Fix a false positive in invalid CAS detection that when the last data
stored in CAS just fits inside the DataPool, validation is erroneously
think the data stored pass the end of the storage.

The error happens when the size of the data is alignment - 1, as the
null termination padding will make the end of the data matches the end
of the data pool.

rdar://150386374

Author: cachemeifyoucan

llvm/lib/CAS/OnDiskGraphDB.cpp

@@ -966,7 +966,7 @@ Error OnDiskGraphDB::validate(bool Deep, HashingFuncT Hasher) const {
       llvm_unreachable("already handled");
     case TrieRecord::StorageKind::DataPool: {
       auto DataRecord = DataRecordHandle::get(DataPool.beginData(D.Offset));
-      if (DataRecord.getTotalSize() + D.Offset.get() >= DataPool.size())
+      if (DataRecord.getTotalSize() + D.Offset.get() > DataPool.size())
         return dataError("data record span passed the end of the data pool");
       for (auto InternRef : DataRecord.getRefs()) {
         auto Index = getIndexProxyFromRef(InternRef);

llvm/test/tools/llvm-cas/validation.test

@@ -1,6 +1,13 @@
 RUN: rm -rf %t
 RUN: mkdir %t
 
+# Ingest a blob which just fits inside the CAS data pool to make sure the validate passes.
+RUN: truncate -s 7 %t/file
+RUN: cat %t/file | \
+RUN:   llvm-cas --cas %t/cas  --make-blob \
+RUN:   --data -
+RUN: llvm-cas --cas %t/cas --validate --check-hash
+
 RUN: llvm-cas --cas %t/cas --ingest %S/Inputs > %t/cas.id
 RUN: llvm-cas --cas %t/cas --validate
 RUN: llvm-cas --cas %t/cas --validate --check-hash