netdev - Re: off-by-one in DecodeQ931

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Date:	Tue, 3 May 2016 01:12:06 -0400
From:	Toby DiPasquale <toby@...g.net>
To:	Florian Westphal <fw@...len.de>
Cc:	pablo@...filter.org, Patrick McHardy <kaber@...sh.net>,
	kadlec@...ckhole.kfki.hu, davem@...emloft.net,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org
Subject: Re: off-by-one in DecodeQ931

On Mon, Apr 25, 2016 at 11:29 AM, Florian Westphal <fw@...len.de> wrote:
> -> sz (size_t) will underflow here
>
> I'd suggest to change the if (sz < 1) to if (sz < 2) to
> resolve this, the while loop below has to be taken anyway.

Thanks, Florian! Updated patch below:

Signed-off-by: Toby DiPasquale <toby@...g.net>

diff --git a/net/netfilter/nf_conntrack_h323_asn1.c
b/net/netfilter/nf_conntrack_h323_asn1.c
index bcd5ed6..89b2e46 100644
--- a/net/netfilter/nf_conntrack_h323_asn1.c
+++ b/net/netfilter/nf_conntrack_h323_asn1.c
@@ -846,9 +846,10 @@ int DecodeQ931(unsigned char *buf, size_t sz, Q931 *q931)
        sz -= len;

        /* Message Type */
-       if (sz < 1)
+       if (sz < 2)
                return H323_ERROR_BOUND;
        q931->MessageType = *p++;
+       sz--;
        PRINT("MessageType = %02X\n", q931->MessageType);
        if (*p & 0x80) {
                p++;