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

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Date:   Mon, 5 Sep 2016 16:22:39 +0200
From:   Daniel Mack <daniel@...que.org>
To:     Daniel Borkmann <daniel@...earbox.net>, htejun@...com, ast@...com
Cc:     davem@...emloft.net, kafai@...com, fw@...len.de,
        pablo@...filter.org, harald@...hat.com, netdev@...r.kernel.org,
        sargun@...gun.me
Subject: Re: [PATCH v3 5/6] net: core: run cgroup eBPF egress programs

On 08/30/2016 12:03 AM, Daniel Borkmann wrote:
> On 08/26/2016 09:58 PM, Daniel Mack wrote:

>> 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.

Ah, right.

> 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?

Hmm, I wonder where this hook could be put instead then. When placed in
ip_output() and ip6_output(), the mac headers cannot be pushed before
running the program, resulting in bogus skb data from the eBPF program.

Also, if I read the code correctly, ip[6]_output is not called for
multicast packets.

Any other ideas?


Thanks,
Daniel