From f2380a53fb84d370eaf6e6c3473062c54c57fac7 Mon Sep 17 00:00:00 2001
From: Oliver Giles <ohw.giles@gmail.com>
Date: Mon, 1 Feb 2021 10:12:16 +1300
Subject: [PATCH] Prevent potential double-free in TNEFSubjectHandler

If TNEFSubjectHandler is called multiple times, but the last time
failed due to the PREALLOCCHECK, the subject.data member will be
a freed, but invalid pointer. To prevent a double-free next time
TNEFSubjectHandler is entered, set it to zero after freeing.

Resolves: #85
Reported-by: jasperla
---
 lib/ytnef.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/ytnef.c b/lib/ytnef.c
index b148719..b06c807 100644
--- a/lib/ytnef.c
+++ b/lib/ytnef.c
@@ -301,8 +301,10 @@ int TNEFFromHandler STD_ARGLIST {
 }
 // -----------------------------------------------------------------------------
 int TNEFSubjectHandler STD_ARGLIST {
-  if (TNEF->subject.data)
+  if (TNEF->subject.data) {
     free(TNEF->subject.data);
+    TNEF->subject.data = NULL;
+  }
 
   PREALLOCCHECK(size, 100);
   TNEF->subject.data = calloc(size+1, sizeof(BYTE));