netdev - Re: [PATCH bpf-next] net: Don't uninstall an XDP program when none is installed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 12 Jun 2019 14:15:06 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH bpf-next] net: Don't uninstall an XDP program when none
 is installed

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@...lanox.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.

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);