linux-kernel - Re: [PATCH v16 06/12] bpf: Add bpf_lookup_*_key() and bpf_key

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Date:   Tue, 6 Sep 2022 11:45:27 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Mykola Lysenko <mykolal@...com>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Shuah Khan <shuah@...nel.org>, bpf <bpf@...r.kernel.org>,
        keyrings@...r.kernel.org,
        LSM List <linux-security-module@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Müller <deso@...teo.net>,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v16 06/12] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

On Tue, Sep 6, 2022 at 1:01 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
>
> > > +struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags)
> > > +{
> > > +       key_ref_t key_ref;
> > > +       struct bpf_key *bkey;
> > > +
> > > +       if (flags & ~KEY_LOOKUP_ALL)
> > > +               return NULL;
> > > +
> > > +       /*
> > > +        * Permission check is deferred until the key is used, as
> > > the
> > > +        * intent of the caller is unknown here.
> > > +        */
> > > +       key_ref = lookup_user_key(serial, flags,
> > > KEY_DEFER_PERM_CHECK);
> > > +       if (IS_ERR(key_ref))
> > > +               return NULL;
> > > +
> > > +       bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC);
> >
> > Since this function (due to lookup_user_key) is sleepable, do we
> > really need GFP_ATOMIC here?
>
> Daniel suggested it for bpf_lookup_system_key(), so that the kfunc does
> not have to be sleepable.

Hold on. It has to be sleepable. Just take a look
at what lookup_user_key is doing inside.

> For symmetry, I did the same to
> bpf_lookup_user_key(). Will switch back to GFP_KERNEL.
>
> Thanks
>
> Roberto
>