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Date: Sun, 23 Dec 2012 22:04:54 +0530
From: Dhiru Kholia <dhiru.kholia@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: scan-build results, part 1
On Sun, Dec 23, 2012 at 9:46 PM, magnum <john.magnum@...hmail.com> wrote:
> Another weird complaint is for MSCHAPv2. The pos pointer is set to non-null in line 429. How could it ever be a null dereference in line 433?
I have received an "official" answer on this one. It is *not* a false
positive. "ciphertext" can be NULL and we haven't checked for it
before doing pointer arithmetic on line 429.
gwynne> From the analyzer's point of view, NULL acts like NaN; i.e.
"NULL + anything = NULL" in terms of pointer validity.
Following patch makes this problem go away.
diff --git a/src/MSCHAPv2_fmt_plug.c b/src/MSCHAPv2_fmt_plug.c
index d946036..b4c7fcf 100644
--- a/src/MSCHAPv2_fmt_plug.c
+++ b/src/MSCHAPv2_fmt_plug.c
@@ -44,6 +44,7 @@
#include "sha.h"
#include <openssl/des.h>
+#include <assert.h>
#ifndef uchar
#define uchar unsigned char
@@ -426,6 +427,7 @@ static void *mschapv2_get_salt(char *ciphertext)
SHA1_Init(&ctx);
/* Peer Challenge */
+ assert (ciphertext != NULL);
pos = ciphertext + 10 + 16*2 + 1 + 24*2 + 1; /* Skip $MSCHAPv2$,
Authenticator Challenge and Response Hash
memset(tmp, 0, 16);
--
Cheers,
Dhiru
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