On Wed, 12 Jun 2019 at 23:15, Jakub Kicinski
<jakub.kicinski@xxxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> > ---
> > 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);
