Received-SPF: pass (google.com: domain of linux-kernel+bounces-130598-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Feedback-ID: i56a14606:Fastmail
User-Agent: Cyrus-JMAP/3.11.0-alpha0-333-gbfea15422e-fm-20240327.001-gbfea1542
Precedence: bulk
MIME-Version: 1.0
Message-Id: <701f8f93-f5fb-408b-822a-37a1d5c424ba@app.fastmail.com>
In-Reply-To: <20240327152358.2368467-20-aleksander.lobakin@intel.com>
References: <20240327152358.2368467-1-aleksander.lobakin@intel.com>
 <20240327152358.2368467-20-aleksander.lobakin@intel.com>
Date: Wed, 03 Apr 2024 22:59:36 +0200
From: "Arnd Bergmann" <arnd@arndb.de>
To: "Alexander Lobakin" <aleksander.lobakin@intel.com>,
 "David S . Miller" <davem@davemloft.net>,
 "Eric Dumazet" <edumazet@google.com>, "Jakub Kicinski" <kuba@kernel.org>,
 "Paolo Abeni" <pabeni@redhat.com>
Cc: "Yury Norov" <yury.norov@gmail.com>,
 "Alexander Potapenko" <glider@google.com>,
 nex.sw.ncis.osdt.itp.upstreaming@intel.com,
 "intel-wired-lan@lists.osuosl.org" <intel-wired-lan@lists.osuosl.org>,
 Netdev <netdev@vger.kernel.org>, linux-kernel@vger.kernel.org,
 "Michal Swiatkowski" <michal.swiatkowski@linux.intel.com>,
 "Marcin Szycik" <marcin.szycik@linux.intel.com>,
 "Simon Horman" <horms@kernel.org>, "Kees Cook" <keescook@chromium.org>
Subject: Re: [PATCH net-next v6 19/21] pfcp: always set pfcp metadata
Content-Type: text/plain

On Wed, Mar 27, 2024, at 16:23, Alexander Lobakin wrote:

> +static int pfcp_encap_recv(struct sock *sk, struct sk_buff *skb)
> +{
> +	IP_TUNNEL_DECLARE_FLAGS(flags) = { };
> +	struct metadata_dst *tun_dst;
> +	struct pfcp_metadata *md;
> +	struct pfcphdr *unparsed;
> +	struct pfcp_dev *pfcp;
> +
> +	if (unlikely(!pskb_may_pull(skb, PFCP_HLEN)))
> +		goto drop;
> +
> +	pfcp = rcu_dereference_sk_user_data(sk);
> +	if (unlikely(!pfcp))
> +		goto drop;
> +
> +	unparsed = pfcp_hdr(skb);
> +
> +	ip_tunnel_flags_zero(flags);
> +	tun_dst = udp_tun_rx_dst(skb, sk->sk_family, flags, 0,
> +				 sizeof(*md));
> +	if (unlikely(!tun_dst))
> +		goto drop;
> +
> +	md = ip_tunnel_info_opts(&tun_dst->u.tun_info);
> +	if (unlikely(!md))
> +		goto drop;
> +
> +	if (unparsed->flags & PFCP_SEID_FLAG)
> +		pfcp_session_recv(pfcp, skb, md);
> +	else
> +		pfcp_node_recv(pfcp, skb, md);
> +
> +	__set_bit(IP_TUNNEL_PFCP_OPT_BIT, flags);
> +	ip_tunnel_info_opts_set(&tun_dst->u.tun_info, md, sizeof(*md),
> +				flags);
> +

The memcpy() in the ip_tunnel_info_opts_set() causes
a string.h fortification warning, with at least gcc-13:

    In function 'fortify_memcpy_chk',
        inlined from 'ip_tunnel_info_opts_set' at include/net/ip_tunnels.h:619:3,
        inlined from 'pfcp_encap_recv' at drivers/net/pfcp.c:84:2:
    include/linux/fortify-string.h:553:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
      553 |                         __write_overflow_field(p_size_field, size);

As far as I can tell, the warning is caused by the
ambiguity of the union, but what I noticed is that
it also seems to copy a buffer to itself, as 'md'
is initialized to tun_dst->u.tun_info as well.

Is this intentional?

      Arnd