From ca11026a032ce2a3de4b3c389ee53d2bdc8794d6 Mon Sep 17 00:00:00 2001
From: Paul Wankadia <junyer@google.com>
Date: Tue, 14 Jul 2020 10:23:46 -0700
Subject: [PATCH] Make Regexp::Simplify() return a null pointer when stopped
 early.

Change-Id: I19e447e6c7dec34201299a12104e72bf7e792a9e
Reviewed-on: https://code-review.googlesource.com/c/re2/+/57570
Reviewed-by: Paul Wankadia <junyer@google.com>
---
 re2/prefilter.cc |  5 +++--
 re2/simplify.cc  | 14 +++++++++++---
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/re2/prefilter.cc b/re2/prefilter.cc
index f61d54b8f..a47b3120f 100644
--- a/re2/prefilter.cc
+++ b/re2/prefilter.cc
@@ -648,14 +648,15 @@ Prefilter* Prefilter::FromRegexp(Regexp* re) {
     return NULL;
 
   Regexp* simple = re->Simplify();
-  Prefilter::Info *info = BuildInfo(simple);
+  if (simple == NULL)
+    return NULL;
 
+  Prefilter::Info* info = BuildInfo(simple);
   simple->Decref();
   if (info == NULL)
     return NULL;
 
   Prefilter* m = info->TakeMatch();
-
   delete info;
   return m;
 }
diff --git a/re2/simplify.cc b/re2/simplify.cc
index 270f0ff95..663d5fcd4 100644
--- a/re2/simplify.cc
+++ b/re2/simplify.cc
@@ -28,8 +28,6 @@ bool Regexp::SimplifyRegexp(const StringPiece& src, ParseFlags flags,
   Regexp* sre = re->Simplify();
   re->Decref();
   if (sre == NULL) {
-    // Should not happen, since Simplify never fails.
-    LOG(ERROR) << "Simplify failed on " << src;
     if (status) {
       status->set_code(kRegexpInternalError);
       status->set_error_arg(src);
@@ -180,10 +178,20 @@ Regexp* Regexp::Simplify() {
   CoalesceWalker cw;
   Regexp* cre = cw.Walk(this, NULL);
   if (cre == NULL)
-    return cre;
+    return NULL;
+  if (cw.stopped_early()) {
+    cre->Decref();
+    return NULL;
+  }
   SimplifyWalker sw;
   Regexp* sre = sw.Walk(cre, NULL);
   cre->Decref();
+  if (sre == NULL)
+    return NULL;
+  if (sw.stopped_early()) {
+    sre->Decref();
+    return NULL;
+  }
   return sre;
 }