Refuse to rewrite when MaxSubmatch() is too large. Change-Id: I76f1d92586c3e0f4895ceb16fb019951843497f8 Reviewed-on: https://code-review.googlesource.com/c/re2/+/56870 Reviewed-by: Paul Wankadia <junyer@google.com>

diff --git a/re2/re2.cc b/re2/re2.cc
index 69258af..35fd1cc 100644
--- a/re2/re2.cc
+++ b/re2/re2.cc

@@ -405,6 +405,8 @@
                   const StringPiece& rewrite) {
   StringPiece vec[kVecSize];
   int nvec = 1 + MaxSubmatch(rewrite);
+  if (nvec > 1 + re.NumberOfCapturingGroups())
+    return false;
   if (nvec > static_cast<int>(arraysize(vec)))
     return false;
   if (!re.Match(*str, 0, str->size(), UNANCHORED, vec, nvec))
@@ -425,6 +427,8 @@
                        const StringPiece& rewrite) {
   StringPiece vec[kVecSize];
   int nvec = 1 + MaxSubmatch(rewrite);
+  if (nvec > 1 + re.NumberOfCapturingGroups())
+    return false;
   if (nvec > static_cast<int>(arraysize(vec)))
     return false;
 
@@ -497,9 +501,10 @@
                   std::string* out) {
   StringPiece vec[kVecSize];
   int nvec = 1 + MaxSubmatch(rewrite);
+  if (nvec > 1 + re.NumberOfCapturingGroups())
+    return false;
   if (nvec > static_cast<int>(arraysize(vec)))
     return false;
-
   if (!re.Match(text, 0, text.size(), UNANCHORED, vec, nvec))
     return false;
 
@@ -1012,8 +1017,8 @@
       int n = (c - '0');
       if (n >= veclen) {
         if (options_.log_errors()) {
-          LOG(ERROR) << "requested group " << n
-                     << " in regexp " << rewrite.data();
+          LOG(ERROR) << "invalid substitution \\" << n
+                     << " from " << veclen << " groups";
         }
         return false;
       }

diff --git a/re2/testing/re2_test.cc b/re2/testing/re2_test.cc
index 52e1f6f..ec457fb 100644
--- a/re2/testing/re2_test.cc
+++ b/re2/testing/re2_test.cc

@@ -224,6 +224,15 @@
   ASSERT_EQ(s, "'foo'");
 }
 
+TEST(RE2, MaxSubmatchTooLarge) {
+  std::string s;
+  ASSERT_FALSE(RE2::Extract("foo", "f(o+)", "\\1\\2", &s));
+  s = "foo";
+  ASSERT_FALSE(RE2::Replace(&s, "f(o+)", "\\1\\2"));
+  s = "foo";
+  ASSERT_FALSE(RE2::GlobalReplace(&s, "f(o+)", "\\1\\2"));
+}
+
 TEST(RE2, Consume) {
   RE2 r("\\s*(\\w+)");    // matches a word, possibly proceeded by whitespace
   std::string word;