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    SubjectRe: [PATCH net-next v6 19/21] pfcp: always set pfcp metadata
    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

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