Toby DiPasquale <toby@xxxxxxxx> wrote:
> I was reviewing the H.323 conntrack helper in the kernel when I came
> across what appears to be an off-by-one error in the DecodeQ931
> function. The MessageType field of the Q931 record is assigned and p
> is incremented, but the corresponding decrement to sz is missing,
> leading the sz variable to be one more than it should be. This patch
> decrements sz so it is the proper value going into the parsing of the
> information elements.
>
> Signed-off-by: Toby DiPasquale <toby@xxxxxxxx>
Looks correct, BUT
> diff --git a/net/netfilter/nf_conntrack_h323_asn1.c
> b/net/netfilter/nf_conntrack_h323_asn1.c
> index bcd5ed6..68b1557 100644
> --- a/net/netfilter/nf_conntrack_h323_asn1.c
> +++ b/net/netfilter/nf_conntrack_h323_asn1.c
> @@ -849,6 +849,7 @@ int DecodeQ931(unsigned char *buf, size_t sz, Q931 *q931)
> if (sz < 1)
> return H323_ERROR_BOUND;
sz can be 1
> q931->MessageType = *p++;
> + sz--;
sz is now 0
> PRINT("MessageType = %02X\n", q931->MessageType);
> if (*p & 0x80) {
> p++;
> sz--;
-> 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.
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