Save and restore PL_regeol for op inside of regex (RT ##66110)

If the op inside of a (?{ }) construct is another regex, the two
regexen end up corrupting each others' end-of-string markers,
resulting in various pathologies including access violations,
stack corruptions, and memory use growing without bound.

The change here is intended to be a relatively safe, cheap way to
prevent memory errors and makes no attempt to save and restore
other aspects of regex state; i.e., general purpose reentrancy
for the regex engine is still a TODO.

1 files changed, 2 insertions, 0 deletions

diff --git a/regexec.c b/regexec.c
index f3c9540e8d..d3dd61230b 100644
--- a/regexec.c
+++ b/regexec.c
@@ -3716,6 +3716,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, regnode *prog)
 		OP_4tree * const oop = PL_op;
 		COP * const ocurcop = PL_curcop;
 		PAD *old_comppad;
+		char *saved_regeol = PL_regeol;
 	    
 		n = ARG(scan);
 		PL_op = (OP_4tree*)rexi->data->data[n];
@@ -3741,6 +3742,7 @@ S_regmatch(pTHX_ regmatch_info *reginfo, regnode *prog)
 		PL_op = oop;
 		PAD_RESTORE_LOCAL(old_comppad);
 		PL_curcop = ocurcop;
+		PL_regeol = saved_regeol;
 		if (!logical) {
 		    /* /(?{...})/ */
 		    sv_setsv(save_scalar(PL_replgv), ret);