From 3d6460edeee21d7d790ec570d0887bed1f4366dd Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <daniel@haxx.se>
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(-)

diff --git a/lib/security.c b/lib/security.c
index a268d4a62..4cef8f89f 100644
--- a/lib/security.c
+++ b/lib/security.c
@@ -192,15 +192,18 @@ static CURLcode read_data(struct connectdata *conn,
                           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;