netdev - Re: [PATCH net 2/3] mptcp: Fix out of bounds when parsing TCP options

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Message-ID: <c7caefb9-1aed-5bc9-b429-925412994249@linux.intel.com>
Date:   Wed, 9 Jun 2021 17:07:14 -0700 (PDT)
From:   Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:     Maxim Mikityanskiy <maximmi@...dia.com>
cc:     Matthieu Baerts <matthieu.baerts@...sares.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Patrick McHardy <kaber@...sh.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Christoph Paasch <cpaasch@...le.com>,
        Peter Krystad <peter.krystad@...ux.intel.com>,
        Young Xiao <92siuyang@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net 2/3] mptcp: Fix out of bounds when parsing TCP
 options

On Wed, 9 Jun 2021, Maxim Mikityanskiy wrote:

> The TCP option parser in mptcp (mptcp_get_options) could read one byte
> out of bounds. When the length is 1, the execution flow gets into the
> loop, reads one byte of the opcode, and if the opcode is neither
> TCPOPT_EOL nor TCPOPT_NOP, it reads one more byte, which exceeds the
> length of 1.
>
> This fix is inspired by commit 9609dad263f8 ("ipv4: tcp_input: fix stack
> out of bounds when parsing TCP options.").
>
> Cc: Young Xiao <92siuyang@...il.com>
> Fixes: cec37a6e41aa ("mptcp: Handle MP_CAPABLE options for outgoing connections")
> Signed-off-by: Maxim Mikityanskiy <maximmi@...dia.com>
> ---
> net/mptcp/options.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/mptcp/options.c b/net/mptcp/options.c
> index 6b825fb3fa83..9b263f27ce9b 100644
> --- a/net/mptcp/options.c
> +++ b/net/mptcp/options.c
> @@ -356,6 +356,8 @@ void mptcp_get_options(const struct sk_buff *skb,
> 			length--;
> 			continue;
> 		default:
> +			if (length < 2)
> +				return;
> 			opsize = *ptr++;
> 			if (opsize < 2) /* "silly options" */
> 				return;
> -- 
> 2.25.1

Florian's comment on patch 1 prompted me to double-check th->doff 
validation, and for MPTCP we're covered by the check in tcp_v4_rcv(). So 
this patch looks good:

Reviewed-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>

If you send a v2 series, please also cc: mptcp@...ts.linux.dev

Thanks!

--
Mat Martineau
Intel