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.
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);
