netdev - Re: [PATCH bpf] libbpf: fix to reject unknown flags in xsk_socket_

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Date:   Mon, 11 Mar 2019 18:03:51 +0100
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Magnus Karlsson <magnus.karlsson@...el.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Maciej Fijalkowski <maciejromanfijalkowski@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf] libbpf: fix to reject unknown flags in xsk_socket__create()

On Mon, Mar 11, 2019 at 5:54 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Mon, Mar 11, 2019 at 7:52 AM Magnus Karlsson
> <magnus.karlsson@...el.com> wrote:
> >
> > In xsk_socket__create(), the libbpf_flags field was not checked for
> > setting currently unused/unknown flags. This patch fixes that by returning
> > -EINVAL if the user has set any flag that is not in use at this point
> > in time.
> >
> > Fixes: 1cad07884239 ("libbpf: add support for using AF_XDP sockets")
> > Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> > ---
> >  tools/lib/bpf/xsk.c | 15 +++++++++++----
> >  1 file changed, 11 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> > index f98ac82..912f942 100644
> > --- a/tools/lib/bpf/xsk.c
> > +++ b/tools/lib/bpf/xsk.c
> > @@ -126,8 +126,8 @@ static void xsk_set_umem_config(struct xsk_umem_config *cfg,
> >         cfg->frame_headroom = usr_cfg->frame_headroom;
> >  }
> >
> > -static void xsk_set_xdp_socket_config(struct xsk_socket_config *cfg,
> > -                                     const struct xsk_socket_config *usr_cfg)
> > +static int xsk_set_xdp_socket_config(struct xsk_socket_config *cfg,
> > +                                    const struct xsk_socket_config *usr_cfg)
> >  {
> >         if (!usr_cfg) {
> >                 cfg->rx_size = XSK_RING_CONS__DEFAULT_NUM_DESCS;
> > @@ -135,14 +135,19 @@ static void xsk_set_xdp_socket_config(struct xsk_socket_config *cfg,
> >                 cfg->libbpf_flags = 0;
> >                 cfg->xdp_flags = 0;
> >                 cfg->bind_flags = 0;
> > -               return;
> > +               return 0;
> >         }
> >
> > +       if (cfg->libbpf_flags & ~XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD)
> > +               return -EINVAL;
> > +
>
> Shouldn't this be checking usr_cfg->libbpf_flags instead?

Arrghh! Yes you are of course right. Thanks for catching this. Will spin a v2.

> Also, what about bind_flags and xdp_flags? For those we are deferring
> to underlying systems to check extra flags?

I defer that to the underlying calls so I do not have to keep this
code up to date with changes to those flags.

Thanks: Magnus

>
> >         cfg->rx_size = usr_cfg->rx_size;
> >         cfg->tx_size = usr_cfg->tx_size;
> >         cfg->libbpf_flags = usr_cfg->libbpf_flags;
> >         cfg->xdp_flags = usr_cfg->xdp_flags;
> >         cfg->bind_flags = usr_cfg->bind_flags;
> > +
> > +       return 0;
> >  }
> >
> >  int xsk_umem__create(struct xsk_umem **umem_ptr, void *umem_area, __u64 size,
> > @@ -557,7 +562,9 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
> >         }
> >         strncpy(xsk->ifname, ifname, IFNAMSIZ);
> >
> > -       xsk_set_xdp_socket_config(&xsk->config, usr_config);
> > +       err = xsk_set_xdp_socket_config(&xsk->config, usr_config);
> > +       if (err)
> > +               goto out_socket;
> >
> >         if (rx) {
> >                 err = setsockopt(xsk->fd, SOL_XDP, XDP_RX_RING,
> > --
> > 2.7.4
> >