From: Daniel Borkmann <daniel@iogearbox•net>
To: John Fastabend <john.fastabend@gmail•com>,
Jesper Dangaard Brouer <brouer@redhat•com>
Cc: netdev@vger•kernel.org, "David S. Miller" <davem@davemloft•net>,
Andy Gospodarek <andy@greyhouse•net>
Subject: Re: [PATCH net-next] xdp: implement xdp_redirect_map for generic XDP
Date: Wed, 06 Sep 2017 20:51:38 +0200 [thread overview]
Message-ID: <59B043BA.1030001@iogearbox.net> (raw)
In-Reply-To: <59B0418A.5090609@gmail.com>
On 09/06/2017 08:42 PM, John Fastabend wrote:
> On 09/06/2017 11:18 AM, Jesper Dangaard Brouer wrote:
>> On Wed, 06 Sep 2017 18:24:07 +0200
>> Daniel Borkmann <daniel@iogearbox•net> wrote:
>>> On 09/06/2017 05:26 PM, Jesper Dangaard Brouer wrote:
>>>> Using bpf_redirect_map is allowed for generic XDP programs, but the
>>>> appropriate map lookup was never performed in xdp_do_generic_redirect().
>>>>
>>>> Instead the map-index is directly used as the ifindex. For the
>>>
>>> Good point, but ...
>>>
>>> [...]
>>>> net/core/filter.c | 29 +++++++++++++++++++++++++++++
>>>> 1 file changed, 29 insertions(+)
>>>>
>>>> diff --git a/net/core/filter.c b/net/core/filter.c
>>>> index 5912c738a7b2..6a4745bf2c9f 100644
>>>> --- a/net/core/filter.c
>>>> +++ b/net/core/filter.c
>>>> @@ -2562,6 +2562,32 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
>>>> }
>>>> EXPORT_SYMBOL_GPL(xdp_do_redirect);
>>>>
>>>> +static int xdp_do_generic_redirect_map(struct net_device *dev,
>>>> + struct sk_buff *skb,
>>>> + struct bpf_prog *xdp_prog)
>>>> +{
>>>> + struct redirect_info *ri = this_cpu_ptr(&redirect_info);
>>>> + struct bpf_map *map = ri->map;
>>>> + u32 index = ri->ifindex;
>>>> + struct net_device *fwd;
>>>> + int err;
>>>> +
>>>> + ri->ifindex = 0;
>>>> + ri->map = NULL;
>>>> +
>>>> + fwd = __dev_map_lookup_elem(map, index);
>>>> + if (!fwd) {
>>>> + err = -EINVAL;
>>>> + goto err;
>>>> + }
>>>> + skb->dev = fwd;
>>>> + _trace_xdp_redirect_map(dev, xdp_prog, fwd, map, index);
>>>> + return 0;
>>>> +err:
>>>> + _trace_xdp_redirect_map_err(dev, xdp_prog, fwd, map, index, err);
>>>> + return err;
>>>> +}
>>>> +
>>>> int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
>>>> struct bpf_prog *xdp_prog)
>>>> {
>>>> @@ -2571,6 +2597,9 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
>>>> unsigned int len;
>>>> int err = 0;
>>>>
>>>> + if (ri->map)
>>>> + return xdp_do_generic_redirect_map(dev, skb, xdp_prog);
>>>
>>> This is not quite correct. Really, the only thing you want
>>> to do here is more or less ...
>>>
>>> int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
>>> struct bpf_prog *xdp_prog)
>>> {
>>> struct redirect_info *ri = this_cpu_ptr(&redirect_info);
>>> struct bpf_map *map = ri->map;
>>> u32 index = ri->ifindex;
>>> struct net_device *fwd;
>>> unsigned int len;
>>> int err = 0;
>>>
>>> ri->ifindex = 0;
>>> ri->map = NULL;
>>>
>>> if (map)
>>> fwd = __dev_map_lookup_elem(map, index);
>>> else
>>> fwd = dev_get_by_index_rcu(dev_net(dev), index);
>>> if (unlikely(!fwd)) {
>>> err = -EINVAL;
>>> goto err;
>>> }
>>> [...]
>>>
>>> ... such that you have a common path to also do the IFF_UP
>>> and MTU checks that are done here, but otherwise omitted in
>>> your patch.
>>
>> Ah, yes. My patch miss the IFF_UP and MTU check. (I was too inspired by
>> xdp_do_redirect_map).
>>
>>> Otherwise it looks good, but note that it also doesn't really
>>> resolve the issue you mention wrt stale map pointers by the
>>> way. [...]
>>
>> I actually discovered more cases where we can crash the kernel :-(
>>
>> E.g. driver not supporting XDP_REDIRECT, are still allowed to load an
>> XDP bpf_prog that call bpf_redirect_map() and set the ->map pointer,
>> but it will never call xdp_do_redirect() (which is responsible for
>> clearing/consuming ->map pointer).
>>
>> Another case: You can also call bpf_redirect_map() and then NOT return
>> XDP_REDIRECT (it is obviously strange, but the bpf-helper API allows it).
>
> I think we can cover both these cases with previous suggestion to check
> prog pointers. Working up a patch now.
Yep, they would both be covered.
prev parent reply other threads:[~2017-09-06 18:51 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-06 15:26 [PATCH net-next] xdp: implement xdp_redirect_map for generic XDP Jesper Dangaard Brouer
2017-09-06 15:44 ` Andy Gospodarek
2017-09-06 16:01 ` Jesper Dangaard Brouer
2017-09-06 16:24 ` Daniel Borkmann
2017-09-06 17:02 ` Daniel Borkmann
2017-09-06 18:18 ` Jesper Dangaard Brouer
2017-09-06 18:42 ` John Fastabend
2017-09-06 18:51 ` Daniel Borkmann [this message]
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