linux-kernel - Re: [PATCH v16 07/12] bpf: Add bpf_verify_pkcs7

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Date:   Tue, 06 Sep 2022 10:07:41 +0200
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>, joannelkoong@...il.com
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, mykolal@...com,
        dhowells@...hat.com, jarkko@...nel.org, rostedt@...dmis.org,
        mingo@...hat.com, paul@...l-moore.com, jmorris@...ei.org,
        serge@...lyn.com, shuah@...nel.org, bpf@...r.kernel.org,
        keyrings@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        deso@...teo.net, Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v16 07/12] bpf: Add bpf_verify_pkcs7_signature() kfunc

On Tue, 2022-09-06 at 04:57 +0200, Kumar Kartikeya Dwivedi wrote:
> On Mon, 5 Sept 2022 at 16:35, Roberto Sassu
> <roberto.sassu@...weicloud.com> wrote:
> > From: Roberto Sassu <roberto.sassu@...wei.com>
> > 
> > Add the bpf_verify_pkcs7_signature() kfunc, to give eBPF security
> > modules
> > the ability to check the validity of a signature against supplied
> > data, by
> > using user-provided or system-provided keys as trust anchor.
> > 
> > The new kfunc makes it possible to enforce mandatory policies, as
> > eBPF
> > programs might be allowed to make security decisions only based on
> > data
> > sources the system administrator approves.
> > 
> > The caller should provide the data to be verified and the signature
> > as eBPF
> > dynamic pointers (to minimize the number of parameters) and a
> > bpf_key
> > structure containing a reference to the keyring with keys trusted
> > for
> > signature verification, obtained from bpf_lookup_user_key() or
> > bpf_lookup_system_key().
> > 
> > For bpf_key structures obtained from the former lookup function,
> > bpf_verify_pkcs7_signature() completes the permission check
> > deferred by
> > that function by calling key_validate(). key_task_permission() is
> > already
> > called by the PKCS#7 code.
> > 
> > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> > Acked-by: KP Singh <kpsingh@...nel.org>
> > ---
> >  kernel/trace/bpf_trace.c | 45
> > ++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 45 insertions(+)
> > 
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 7a7023704ac2..8e2c026b0a58 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1294,12 +1294,57 @@ void bpf_key_put(struct bpf_key *bkey)
> >         kfree(bkey);
> >  }
> > 
> > +#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
> > +/**
> > + * bpf_verify_pkcs7_signature - verify a PKCS#7 signature
> > + * @data_ptr: data to verify
> > + * @sig_ptr: signature of the data
> > + * @trusted_keyring: keyring with keys trusted for signature
> > verification
> > + *
> > + * Verify the PKCS#7 signature *sig_ptr* against the supplied
> > *data_ptr*
> > + * with keys in a keyring referenced by *trusted_keyring*.
> > + *
> > + * Return: 0 on success, a negative value on error.
> > + */
> > +int bpf_verify_pkcs7_signature(struct bpf_dynptr_kern *data_ptr,
> > +                              struct bpf_dynptr_kern *sig_ptr,
> > +                              struct bpf_key *trusted_keyring)
> > +{
> > +       int ret;
> > +
> > +       if (trusted_keyring->has_ref) {
> > +               /*
> > +                * Do the permission check deferred in
> > bpf_lookup_user_key().
> > +                * See bpf_lookup_user_key() for more details.
> > +                *
> > +                * A call to key_task_permission() here would be
> > redundant, as
> > +                * it is already done by keyring_search() called by
> > +                * find_asymmetric_key().
> > +                */
> > +               ret = key_validate(trusted_keyring->key);
> > +               if (ret < 0)
> > +                       return ret;
> > +       }
> > +
> > +       return verify_pkcs7_signature(data_ptr->data,
> > +                                     bpf_dynptr_get_size(data_ptr)
> > ,
> > +                                     sig_ptr->data,
> > +                                     bpf_dynptr_get_size(sig_ptr),
> 
> MIssing check for data_ptr->data == NULL before making this call?
> Same
> for sig_ptr.

Patch 3 requires the dynptrs to be initialized. Isn't enough?

Thanks

Roberto