From 1241deaefb71c40436320af7d0bd04c7c9e54241 Mon Sep 17 00:00:00 2001
From: Qualys Security Advisory <qsa@qualys.com>
Date: Sun, 21 Feb 2021 21:45:19 -0800
Subject: [PATCH] CVE-2020-28009: Integer overflow in get_stdinput()

(cherry picked from commit bbf1bb10bee5a1d7cbcc97f178b348189219eb7d)
---
 src/src/string.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/src/string.c b/src/src/string.c
index f91a6a428..27e030bd8 100644
--- a/src/src/string.c
+++ b/src/src/string.c
@@ -1091,7 +1091,16 @@ existing length of the string. */
 
 unsigned inc = oldsize < 4096 ? 127 : 1023;
 
+if (g->ptr < 0 || g->ptr > g->size || g->size >= INT_MAX/2)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE,
+    "internal error in gstring_grow (ptr %d size %d)", g->ptr, g->size);
+
 if (count <= 0) return;
+
+if (count >= INT_MAX/2 - g->ptr)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE,
+    "internal error in gstring_grow (ptr %d count %d)", g->ptr, count);
+
 g->size = (p + count + inc + 1) & ~inc;		/* one for a NUL */
 
 /* Try to extend an existing allocation. If the result of calling
@@ -1140,6 +1149,10 @@ string_catn(gstring * g, const uschar *s, int count)
 int p;
 BOOL srctaint = is_tainted(s);
 
+if (count < 0)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE,
+    "internal error in string_catn (count %d)", count);
+
 if (!g)
   {
   unsigned inc = count < 4096 ? 127 : 1023;
@@ -1149,8 +1162,12 @@ if (!g)
 else if (srctaint && !is_tainted(g->s))
   gstring_rebuffer(g);
 
+if (g->ptr < 0 || g->ptr > g->size)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE,
+    "internal error in string_catn (ptr %d size %d)", g->ptr, g->size);
+
 p = g->ptr;
-if (p + count >= g->size)
+if (count >= g->size - p)
   gstring_grow(g, count);
 
 /* Because we always specify the exact number of characters to copy, we can
-- 
2.30.2