From d77d726d206f16232df6edd80739720bb7011aea Mon Sep 17 00:00:00 2001
From: Pali <pali@cpan.org>
Date: Thu, 7 Oct 2021 22:35:51 +0200
Subject: [PATCH] Fix memory leak in function encode_method()

Pull request https://github.com/dankogai/p5-encode/pull/72 fixed memory
corruption but introduced a new memory leak as dst scalar is not mortal
anymore and not every possible exit from every XS function properly release
scalar's memory.

Fix this memory leak by making dst scalar mortal again. To not re-introduce
that memory corruption, first store dst scalar into temporary variable and
then save it into stack via ST(0) macro.
---
 Encode.xs | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/Encode.xs b/Encode.xs
index 4baf296..d173c96 100644
--- a/Encode.xs
+++ b/Encode.xs
@@ -154,7 +154,7 @@ encode_method(pTHX_ const encode_t * enc, const encpage_t * dir, SV * src, U8 *
     STRLEN sdone = 0;
     /* We allocate slen+1.
        PerlIO dumps core if this value is smaller than this. */
-    SV *dst = newSV(slen+1);
+    SV *dst = sv_2mortal(newSV(slen+1));
     U8 *d = (U8 *)SvPVX(dst);
     STRLEN dlen = SvLEN(dst)-1;
     int code = 0;
@@ -810,13 +810,12 @@ CODE:
     tmp = encode_method(aTHX_ enc, enc->t_utf8, src, s, slen, check,
                 &offset, term, &code, fallback_cb);
     sv_catsv(dst, tmp);
-    SvREFCNT_dec(tmp);
     SvIV_set(off, (IV)offset);
     RETVAL = (code == ENCODE_FOUND_TERM);
 OUTPUT:
     RETVAL
 
-SV *
+void
 Method_decode(obj,src,check_sv = &PL_sv_no)
 SV *	obj
 SV *	src
@@ -828,6 +827,7 @@ PREINIT:
     encode_t *enc;
     U8 *s;
     STRLEN slen;
+    SV *ret;
 INIT:
     SvGETMAGIC(src);
     SvGETMAGIC(check_sv);
@@ -841,13 +841,13 @@ CODE:
     s = modify ? (U8 *)SvPV_force_nomg(src, slen) : (U8 *)SvPV_nomg(src, slen);
     if (SvUTF8(src))
         utf8_safe_downgrade(aTHX_ &src, &s, &slen, modify);
-    RETVAL = encode_method(aTHX_ enc, enc->t_utf8, src, s, slen, check,
+    ret = encode_method(aTHX_ enc, enc->t_utf8, src, s, slen, check,
               NULL, Nullsv, NULL, fallback_cb);
-    SvUTF8_on(RETVAL);
-OUTPUT:
-    RETVAL
+    SvUTF8_on(ret);
+    ST(0) = ret;
+    XSRETURN(1);
 
-SV *
+void
 Method_encode(obj,src,check_sv = &PL_sv_no)
 SV *	obj
 SV *	src
@@ -859,6 +859,7 @@ PREINIT:
     encode_t *enc;
     U8 *s;
     STRLEN slen;
+    SV *ret;
 INIT:
     SvGETMAGIC(src);
     SvGETMAGIC(check_sv);
@@ -872,10 +873,10 @@ CODE:
     s = modify ? (U8 *)SvPV_force_nomg(src, slen) : (U8 *)SvPV_nomg(src, slen);
     if (!SvUTF8(src))
         utf8_safe_upgrade(aTHX_ &src, &s, &slen, modify);
-    RETVAL = encode_method(aTHX_ enc, enc->f_utf8, src, s, slen, check,
+    ret = encode_method(aTHX_ enc, enc->f_utf8, src, s, slen, check,
               NULL, Nullsv, NULL, fallback_cb);
-OUTPUT:
-    RETVAL
+    ST(0) = ret;
+    XSRETURN(1);
 
 bool
 Method_needs_lines(obj)
-- 
2.31.1