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From: "Björn Töpel" <bjorn.topel@gmail.com>
To: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: "Maxim Mikityanskiy" <maximmi@mellanox.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Björn Töpel" <bjorn.topel@intel.com>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	"Saeed Mahameed" <saeedm@mellanox.com>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>
Subject: Re: [PATCH bpf-next] net: Don't uninstall an XDP program when none is installed
Date: Thu, 13 Jun 2019 11:04:45 +0200
Message-ID: <CAJ+HfNg8C+teCywDDjKY6_gdPsg_dzm1cMNFhj7gLps6RYMAJQ@mail.gmail.com> (raw)
In-Reply-To: <20190612141506.7900e952@cakuba.netronome.com>

On Wed, 12 Jun 2019 at 23:15, Jakub Kicinski
<jakub.kicinski@netronome.com> wrote:
>
> On Wed, 12 Jun 2019 16:14:18 +0000, Maxim Mikityanskiy wrote:
> > dev_change_xdp_fd doesn't perform any checks in case it uninstalls an
> > XDP program. It means that the driver's ndo_bpf can be called with
> > XDP_SETUP_PROG asking to set it to NULL even if it's already NULL. This
> > case happens if the user runs `ip link set eth0 xdp off` when there is
> > no XDP program attached.
> >
> > The drivers typically perform some heavy operations on XDP_SETUP_PROG,
> > so they all have to handle this case internally to return early if it
> > happens. This patch puts this check into the kernel code, so that all
> > drivers will benefit from it.
> >
> > Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
> > ---
> > Björn, please take a look at this, Saeed told me you were doing
> > something related, but I couldn't find it. If this fix is already
> > covered by your work, please tell about that.
> >
> >  net/core/dev.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 66f7508825bd..68b3e3320ceb 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -8089,6 +8089,9 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
> >                       bpf_prog_put(prog);
> >                       return -EINVAL;
> >               }
> > +     } else {
> > +             if (!__dev_xdp_query(dev, bpf_op, query))
> > +                     return 0;
>
> This will mask the error if program is installed with different flags.
>

Hmm, probably missing something, but I fail to see how the error is
being masked? This is to catch the NULL-to-NULL case early.

> You driver should do nothing is program installation state did not
> change.  I.e.:
>
>         if (!!prog == !!oldprog)
>
> You can't remove the active -> active check anyway, this change should
> make no difference.
>
> >       }
> >
> >       err = dev_xdp_install(dev, bpf_op, extack, flags, prog);

  reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-12 16:14 Maxim Mikityanskiy
2019-06-12 18:39 ` Björn Töpel
2019-06-12 21:15 ` Jakub Kicinski
2019-06-13  9:04   ` Björn Töpel [this message]
2019-06-13 17:26     ` Jakub Kicinski
2019-07-10 11:16 ` Maxim Mikityanskiy
2019-07-12 15:44   ` Daniel Borkmann
2019-08-14 14:34     ` [PATCH bpf-next v2] net: Don't call XDP_SETUP_PROG when nothing is changed Maxim Mikityanskiy
2019-08-14 17:57       ` Jonathan Lemon
2019-08-14 22:01       ` Jakub Kicinski
2019-08-17 21:29       ` Daniel Borkmann

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