From: Ido Schimmel <idosch@idosch•org>
To: nb <nikolay.borisov@virtuozzo•com>
Cc: nhorman@tuxdriver•com, davem@davemloft•net, kuba@kernel•org,
pabeni@redhat•com, netdev@vger•kernel.org, kernel@virtuozzo•com
Subject: Re: [PATCH net-next v2 1/3] drop_monitor: Implement namespace filtering/reporting for software drops
Date: Wed, 23 Nov 2022 20:10:14 +0200 [thread overview]
Message-ID: <Y35iBgeq5iKyTmfT@shredder> (raw)
In-Reply-To: <7a8bf56c-3db8-63c2-8440-7bbbfb4901ac@virtuozzo.com>
On Wed, Nov 23, 2022 at 05:21:23PM +0200, nb wrote:
>
>
> On 23.11.22 г. 17:16 ч., Ido Schimmel wrote:
> > On Wed, Nov 23, 2022 at 04:28:15PM +0200, Nikolay Borisov wrote:
> > > static void trace_drop_common(struct sk_buff *skb, void *location)
> > > {
> > > struct net_dm_alert_msg *msg;
> > > @@ -219,7 +233,11 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
> > > int i;
> > > struct sk_buff *dskb;
> > > struct per_cpu_dm_data *data;
> > > - unsigned long flags;
> > > + unsigned long flags, ns_id = 0;
> > > +
> > > + if (skb->dev && net_dm_ns &&
> > > + dev_net(skb->dev)->ns.inum != net_dm_ns)
> >
> > I don't think this is going to work, unfortunately. 'skb->dev' is in a
> > union with 'dev_scratch' so 'skb->dev' does not necessarily point to a
> > valid netdev at all times. It can explode when dev_net() tries to
> > dereference it.
> >
> > __skb_flow_dissect() is doing something similar, but I believe there the
> > code paths were audited to make sure it is safe.
> >
> > Did you consider achieving this functionality with a BPF program
> > attached to skb::kfree_skb tracepoint? I believe BPF programs are run
> > with page faults disabled, so it should be safe to attempt this there.
>
> How would that be different than the trace_drop_common which is called as
> part of the trace_kfree_skb, as it's really passed as trace point probe via:
Consider this call path:
__udp_queue_rcv_skb()
__udp_enqueue_schedule_skb()
udp_set_dev_scratch() // skb->dev is not NULL, but not a pointer to a netdev either
// error is returned
kfree_skb_reason() // probe is called
dev_net(skb->dev) in the probe will try to dereference skb->dev and
crash.
On the other hand, a BPF program that is registered as another probe on
the tracepoint will access the memory via bpf_probe_read_kernel(), which
will try to safely read the memory and return an error if it can't. You
can do that today without any kernel changes.
next prev parent reply other threads:[~2022-11-23 18:14 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-23 14:28 [PATCH net-next v2 0/3] Add support for netnamespace filtering in drop monitor Nikolay Borisov
2022-11-23 14:28 ` [PATCH net-next v2 1/3] drop_monitor: Implement namespace filtering/reporting for software drops Nikolay Borisov
2022-11-23 15:16 ` Ido Schimmel
2022-11-23 15:21 ` nb
2022-11-23 18:10 ` Ido Schimmel [this message]
2022-11-24 11:41 ` nb
2022-11-28 7:54 ` Ido Schimmel
2022-11-23 15:33 ` Alexander Lobakin
2022-11-23 16:04 ` nb
2022-11-23 17:16 ` Alexander Lobakin
2022-11-23 14:28 ` [PATCH net-next v2 2/3] drop_monitor: Add namespace filtering/reporting for hardware drops Nikolay Borisov
2022-11-23 15:37 ` Alexander Lobakin
2022-11-23 14:28 ` [PATCH net-next v2 3/3] selftests: net: Add drop monitor tests for namespace filtering functionality Nikolay Borisov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Y35iBgeq5iKyTmfT@shredder \
--to=idosch@idosch$(echo .)org \
--cc=davem@davemloft$(echo .)net \
--cc=kernel@virtuozzo$(echo .)com \
--cc=kuba@kernel$(echo .)org \
--cc=netdev@vger$(echo .)kernel.org \
--cc=nhorman@tuxdriver$(echo .)com \
--cc=nikolay.borisov@virtuozzo$(echo .)com \
--cc=pabeni@redhat$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox