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

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Message-ID: <CAADnVQ+ye+hRB2RvDY+=-kTOhBZesW0fyLR0EY9cV972SwZSSQ@mail.gmail.com>
Date:   Mon, 21 Feb 2022 20:30:04 -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 Mon, Feb 21, 2022 at 6:26 AM Yafang Shao <laoar.shao@...il.com> wrote:
>
> On Mon, Feb 21, 2022 at 4:59 AM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > 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.
>
> I have read through the task_file code, but I haven't found a direct
> way to get the attached cgroups or maps of a specified prog.
> It is easy to look into a cgroup or sockmap, but the key point here is
> which is the proper cgroup or sockmap.
> There are some possible ways to get the attached cgroup or sockmap.
>
> - add new member into struct bpf_prog_aux

No. Please stop proposing kernel changes for your debug needs.

>    For example,
>     struct bpf_prog_aux{
>         union {
>             struct cgroup *attached_cgrp;
>             struct bpf_map *attached_map;
>         };
>     };
>     Then we can easily get the related map or cgroup by extending
> task_file iterator.
>
> - build a table for attached maps, cgroups and etc
>    Like we did for pinned files.
>    Then we can compare the prog with the members stored in this table
> one by one, but that seems a little heavy.
>
> There may be some other ways.

- iterate bpf maps
- find sockmap
- do equivalent of sock_map_progs(), but open coded inside bpf prog
- read progs, print them.