avoid use-after free in /(?{...})/

RT #134208

In something like

    eval { sub { " " }->() =~ /(?{ die })/ }

When the match string gets aliased to $_, the SAVE_DEFSV is done after the
SAVEDESTRUCTOR_X(S_cleanup_regmatch_info_aux).  So if croaking, the SV
gets SvREFCNT_dec()ed by the SAVE_DEFSV, then S_cleanup_regmatch_info_aux()
manipulates the SV's magic.

This doesn't cause a problem unless the match string is temporary, in
which case the only other reference keeping it alive will be removed
by the FREETMPs during the croak.

The fix is to make sure an extra ref to the sv is held.

1 files changed, 1 insertions, 0 deletions

diff --git a/regexp.h b/regexp.h
index 0f35205e1a..ccbc64a009 100644
--- a/regexp.h
+++ b/regexp.h
@@ -658,6 +658,7 @@ typedef struct {
     STRLEN  sublen;     /* saved sublen     field from rex */
     STRLEN  suboffset;  /* saved suboffset  field from rex */
     STRLEN  subcoffset; /* saved subcoffset field from rex */
+    SV      *sv;        /* $_  during (?{}) */
     MAGIC   *pos_magic; /* pos() magic attached to $_ */
     SSize_t pos;        /* the original value of pos() in pos_magic */
     U8      pos_flags;  /* flags to be restored; currently only MGf_BYTES*/