From 7ea481a6471cdad3a674b767f808357b3c7fc721 Mon Sep 17 00:00:00 2001
From: Qualys Security Advisory <qsa@qualys.com>
Date: Sun, 21 Feb 2021 21:49:30 -0800
Subject: [PATCH 13/29] CVE-2020-28024: Heap buffer underflow in smtp_ungetc()

---
 src/smtp_in.c | 3 +++
 src/tls.c     | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/src/smtp_in.c b/src/smtp_in.c
index 16c3a3e33..bdcfde65f 100644
--- a/src/smtp_in.c
+++ b/src/smtp_in.c
@@ -805,6 +805,9 @@ Returns:       the character
 int
 smtp_ungetc(int ch)
 {
+if (smtp_inptr <= smtp_inbuffer)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in smtp_ungetc");
+
 *--smtp_inptr = ch;
 return ch;
 }
diff --git a/src/tls.c b/src/tls.c
index f79bc3193..2a316fe59 100644
--- a/src/tls.c
+++ b/src/tls.c
@@ -151,6 +151,9 @@ Returns:       the character
 int
 tls_ungetc(int ch)
 {
+if (ssl_xfer_buffer_lwm <= 0)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in tls_ungetc");
+
 ssl_xfer_buffer[--ssl_xfer_buffer_lwm] = ch;
 return ch;
 }
-- 
2.30.2