Subject: Re: [PATCH v3 5/6] net: core: run cgroup eBPF egress programs

From: Daniel Borkmann <[email-masked]>
Date: Tue, 30 Aug 2016 00:03:23 +0200

On 08/26/2016 09:58 PM, Daniel Mack wrote:
> If the cgroup associated with the receiving socket has an eBPF
> programs installed, run them from __dev_queue_xmit().
>
> eBPF programs used in this context are expected to either return 1 to
> let the packet pass, or != 1 to drop them. The programs have access to
> the full skb, including the MAC headers.
>
> Note that cgroup_bpf_run_filter() is stubbed out as static inline nop
> for !CONFIG_CGROUP_BPF, and is otherwise guarded by a static key if
> the feature is unused.
>
> Signed-off-by: Daniel Mack <[email-masked]>
> ---
>   net/core/dev.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a75df86..17484e6 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -141,6 +141,7 @@
>   #include <linux/netfilter_ingress.h>
>   #include <linux/sctp.h>
>   #include <linux/crash_dump.h>
> +#include <linux/bpf-cgroup.h>
>
>   #include "net-sysfs.h"
>
> @@ -3329,6 +3330,11 @@ static int __dev_queue_xmit(struct sk_buff *skb, void *accel_priv)
>   	if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP))
>   		__skb_tstamp_tx(skb, NULL, skb->sk, SCM_TSTAMP_SCHED);
>
> +	rc = cgroup_bpf_run_filter(skb->sk, skb,
> +				   BPF_ATTACH_TYPE_CGROUP_INET_EGRESS);
> +	if (rc)
> +		return rc;

This would leak the whole skb by the way.

Apart from that, could this be modeled w/o affecting the forwarding path (at some
local output point where we know to have a valid socket)? Then you could also drop
the !sk and sk->sk_family tests, and we wouldn't need to replicate parts of what
clsact is doing as well. Hmm, maybe access to src/dst mac could be handled to be
just zeroes since not available at that point?

>   	/* Disable soft irqs for various locks below. Also
>   	 * stops preemption for RCU.
>   	 */
>