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    Subject[PATCH 4.19 137/168] net: initialize fastreuse on inet_inherit_port
    Date
    From: Tim Froidcoeur <tim.froidcoeur@tessares.net>

    [ Upstream commit d76f3351cea2d927fdf70dd7c06898235035e84e ]

    In the case of TPROXY, bind_conflict optimizations for SO_REUSEADDR or
    SO_REUSEPORT are broken, possibly resulting in O(n) instead of O(1) bind
    behaviour or in the incorrect reuse of a bind.

    the kernel keeps track for each bind_bucket if all sockets in the
    bind_bucket support SO_REUSEADDR or SO_REUSEPORT in two fastreuse flags.
    These flags allow skipping the costly bind_conflict check when possible
    (meaning when all sockets have the proper SO_REUSE option).

    For every socket added to a bind_bucket, these flags need to be updated.
    As soon as a socket that does not support reuse is added, the flag is
    set to false and will never go back to true, unless the bind_bucket is
    deleted.

    Note that there is no mechanism to re-evaluate these flags when a socket
    is removed (this might make sense when removing a socket that would not
    allow reuse; this leaves room for a future patch).

    For this optimization to work, it is mandatory that these flags are
    properly initialized and updated.

    When a child socket is created from a listen socket in
    __inet_inherit_port, the TPROXY case could create a new bind bucket
    without properly initializing these flags, thus preventing the
    optimization to work. Alternatively, a socket not allowing reuse could
    be added to an existing bind bucket without updating the flags, causing
    bind_conflict to never be called as it should.

    Call inet_csk_update_fastreuse when __inet_inherit_port decides to create
    a new bind_bucket or use a different bind_bucket than the one of the
    listen socket.

    Fixes: 093d282321da ("tproxy: fix hash locking issue when using port redirection in __inet_inherit_port()")
    Acked-by: Matthieu Baerts <matthieu.baerts@tessares.net>
    Signed-off-by: Tim Froidcoeur <tim.froidcoeur@tessares.net>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv4/inet_hashtables.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/net/ipv4/inet_hashtables.c
    +++ b/net/ipv4/inet_hashtables.c
    @@ -161,6 +161,7 @@ int __inet_inherit_port(const struct soc
    return -ENOMEM;
    }
    }
    + inet_csk_update_fastreuse(tb, child);
    }
    inet_bind_hash(child, tb, port);
    spin_unlock(&head->lock);

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