From 91239f7040b1f026d4d15765e7e3f58e92e93761 Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <[email protected]>
Date: Wed, 28 Sep 2016 12:56:02 +0200
Subject: [PATCH] krb5: avoid realloc(0)

If the requested size is zero, bail out with error instead of doing a
realloc() that would cause a double-free: realloc(0) acts as a free()
and then there's a second free in the cleanup path.

CVE-2016-8619

Bug: https://curl.haxx.se/docs/adv_20161102E.html
Reported-by: Cure53
---
 lib/security.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- lib/security.c
+++ lib/security.c
@@ -190,19 +190,22 @@ socket_write(struct connectdata *conn, curl_socket_t fd, const void *to,
 static CURLcode read_data(struct connectdata *conn,
                           curl_socket_t fd,
                           struct krb5buffer *buf)
 {
   int len;
-  void* tmp;
+  void *tmp = NULL;
   CURLcode result;
 
   result = socket_read(fd, &len, sizeof(len));
   if(result)
     return result;
 
-  len = ntohl(len);
-  tmp = realloc(buf->data, len);
+  if(len) {
+    /* only realloc if there was a length */
+    len = ntohl(len);
+    tmp = realloc(buf->data, len);
+  }
   if(tmp == NULL)
     return CURLE_OUT_OF_MEMORY;
 
   buf->data = tmp;
   result = socket_read(fd, buf->data, len);
-- 
2.9.3