From e02d7478ebfc399a9d10ba0df60eee217aa7ab8f Mon Sep 17 00:00:00 2001
From: Karl Williamson <khw@cpan.org>
Date: Fri, 2 Feb 2018 15:14:27 -0700
Subject: (perl #132227) restart a node if we change to uni rules within the
 node and encounter a sharp S

This could lead to a buffer overflow.
---
 regcomp.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/regcomp.c b/regcomp.c
index c6c7cb4925..d79bd191c9 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -13323,6 +13323,18 @@ S_regatom(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, U32 depth)
                          * /u.  This includes the multi-char fold SHARP S to
                          * 'ss' */
                         if (UNLIKELY(ender == LATIN_SMALL_LETTER_SHARP_S)) {
+
+                            /* If the node started out having uni rules, we
+                             * wouldn't have gotten here.  So this means
+                             * something in the middle has changed it, but
+                             * didn't think it needed to reparse.  But this
+                             * sharp s now does indicate the need for
+                             * reparsing. */
+                            if (RExC_uni_semantics) {
+                                p = oldp;
+                                goto loopdone;
+                            }
+
                             RExC_seen_unfolded_sharp_s = 1;
                             maybe_exactfu = FALSE;
                         }
-- 
2.11.0