netdev - Re: [PATCH RFC 2/3] bpf: set attached cgroup name in attach

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Message-ID: <CAADnVQ+FuK2wihDy5GumBN3LVBky0r04CmS4h1JsVoS7QoH6LA@mail.gmail.com>
Date:   Sun, 20 Feb 2022 12:59:46 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH RFC 2/3] bpf: set attached cgroup name in attach_name

On Sun, Feb 20, 2022 at 6:17 AM Yafang Shao <laoar.shao@...il.com> wrote:
>
> On Sun, Feb 20, 2022 at 2:27 AM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > On Fri, Feb 18, 2022 at 1:56 AM Yafang Shao <laoar.shao@...il.com> wrote:
> > >
> > > Set the cgroup path when a bpf prog is attached to a cgroup, and unset
> > > it when the bpf prog is detached.
> > >
> > > Below is the result after this change,
> > > $ cat progs.debug
> > >   id name             attached
> > >    5 dump_bpf_map     bpf_iter_bpf_map
> > >    7 dump_bpf_prog    bpf_iter_bpf_prog
> > >   17 bpf_sockmap      cgroup:/
> > >   19 bpf_redir_proxy
> > >
> > > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > > ---
> > >  kernel/bpf/cgroup.c | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > >
> > > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> > > index 43eb3501721b..ebd87e54f2d0 100644
> > > --- a/kernel/bpf/cgroup.c
> > > +++ b/kernel/bpf/cgroup.c
> > > @@ -440,6 +440,7 @@ static int __cgroup_bpf_attach(struct cgroup *cgrp,
> > >         struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
> > >         struct bpf_cgroup_storage *new_storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
> > >         enum cgroup_bpf_attach_type atype;
> > > +       char cgrp_path[64] = "cgroup:";
> > >         struct bpf_prog_list *pl;
> > >         struct list_head *progs;
> > >         int err;
> > > @@ -508,6 +509,11 @@ static int __cgroup_bpf_attach(struct cgroup *cgrp,
> > >         else
> > >                 static_branch_inc(&cgroup_bpf_enabled_key[atype]);
> > >         bpf_cgroup_storages_link(new_storage, cgrp, type);
> > > +
> > > +       cgroup_name(cgrp, cgrp_path + strlen("cgroup:"), 64);
> > > +       cgrp_path[63] = '\0';
> > > +       prog->aux->attach_name = kstrdup(cgrp_path, GFP_KERNEL);
> > > +
> >
> > This is pure debug code. We cannot have it in the kernel.
> > Not even under #ifdef.
> >
> > Please do such debug code on a side as your own bpf program.
> > For example by kprobe-ing in this function and keeping the path
> > in a bpf map or send it to user space via ringbuf.
> > Or enable cgroup tracepoint and monitor cgroup_mkdir with full path.
> > Record it in user space or in bpf map, etc.
> >
>
> It is another possible solution to  hook the related kernel functions
> or tracepoints, but it may be a little complicated to track all the
> bpf attach types, for example we also want to track
> BPF_PROG_TYPE_SK_MSG[1], BPF_PROG_TYPE_FLOW_DISSECTOR and etc.
> While the attach_name provides us a generic way to get how the bpf
> progs are attached, which can't be got by bpftool.

bpftool can certainly print such details.
See how it's using task_file iterator.
It can be extended to look into cgroups and sockmap,
and for each program print "sockmap:%d", map->id if so desired.