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

[Sargun Dhillon <sargun@sargun.me>]

On Tue, Aug 30, 2016 at 12:03:23AM +0200, Daniel Borkmann wrote:
> 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 <daniel@zonque.org>
> >---
> >  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.
> >  	 */
> >
Given this patchset only effects AF_INET, and AF_INET6, why not put the hooks at 
ip_output, and ip6_output