SERVER-17264: improve bson validation for utf-8 strings

(cherry picked from commit 394a8569ff14a215c0691aa34440227b2e62a4de)

Conflicts:
	src/mongo/bson/bson_validate_test.cpp

2 files changed, 19 insertions, 0 deletions

diff --git a/src/mongo/bson/bson_validate.cpp b/src/mongo/bson/bson_validate.cpp
index 9ac0bcbbbfb..a7c95ad1370 100644
--- a/src/mongo/bson/bson_validate.cpp
+++ b/src/mongo/bson/bson_validate.cpp
@@ -62,6 +62,11 @@ namespace mongo {
                 if ( !readNumber<int>( &sz ) )
                     return Status( ErrorCodes::InvalidBSON, "invalid bson" );
 
+                if ( sz <= 0 ) {
+                    // must have NULL at the very least
+                    return Status( ErrorCodes::InvalidBSON, "invalid bson");
+                }
+
                 if ( out ) {
                     *out = StringData( _buffer + _position, sz );
                 }
diff --git a/src/mongo/bson/bson_validate_test.cpp b/src/mongo/bson/bson_validate_test.cpp
index 61e67f33c46..a36dbc582d6 100644
--- a/src/mongo/bson/bson_validate_test.cpp
+++ b/src/mongo/bson/bson_validate_test.cpp
@@ -213,4 +213,18 @@ namespace {
         ASSERT_NOT_OK(validateBSON(x.objdata(), x.objsize() / 2));
     }
 
+    TEST(BSONValidateFast, StringHasSomething) {
+        BufBuilder bb;
+        BSONObjBuilder ob(bb);
+        bb.appendChar(String);
+        bb.appendStr("x", /*withNUL*/true);
+        bb.appendNum(0);
+        const BSONObj x = ob.done();
+        ASSERT_EQUALS(5 // overhead
+                      + 1 // type
+                      + 2 // name
+                      + 4 // size
+                      , x.objsize());
+        ASSERT_NOT_OK(validateBSON(x.objdata(), x.objsize()));
+    }
 }