Re: [PATCH v15 06/23] Use lsmblob in security_secctx_to_secid

[Casey Schaufler <casey@schaufler-ca.com>]

On 3/6/2020 4:58 PM, Paul Moore wrote:
> On Fri, Feb 14, 2020 at 6:43 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>> Change security_secctx_to_secid() to fill in a lsmblob instead
>> of a u32 secid. Multiple LSMs may be able to interpret the
>> string, and this allows for setting whichever secid is
>> appropriate. In some cases there is scaffolding where other
>> interfaces have yet to be converted.
>>
>> Reviewed-by: Kees Cook <keescook@chromium.org>
>> Reviewed-by: John Johansen <john.johansen@canonical.com>
>> Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
>> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
>> ---
>>  include/linux/security.h          |  5 +++--
>>  kernel/cred.c                     |  4 +---
>>  net/netfilter/nft_meta.c          | 12 +++++++-----
>>  net/netfilter/xt_SECMARK.c        |  5 ++++-
>>  net/netlabel/netlabel_unlabeled.c | 14 ++++++++------
>>  security/security.c               | 18 +++++++++++++++---
>>  6 files changed, 38 insertions(+), 20 deletions(-)
> ...
>
>> diff --git a/net/netfilter/nft_meta.c b/net/netfilter/nft_meta.c
>> index 951b6e87ed5d..e12125b85035 100644
>> --- a/net/netfilter/nft_meta.c
>> +++ b/net/netfilter/nft_meta.c
>> @@ -811,21 +811,23 @@ static const struct nla_policy nft_secmark_policy[NFTA_SECMARK_MAX + 1] = {
>>
>>  static int nft_secmark_compute_secid(struct nft_secmark *priv)
>>  {
>> -       u32 tmp_secid = 0;
>> +       struct lsmblob blob;
>>         int err;
>>
>> -       err = security_secctx_to_secid(priv->ctx, strlen(priv->ctx), &tmp_secid);
>> +       err = security_secctx_to_secid(priv->ctx, strlen(priv->ctx), &blob);
>>         if (err)
>>                 return err;
>>
>> -       if (!tmp_secid)
>> +       if (!lsmblob_is_set(&blob))
>>                 return -ENOENT;
>>
>> -       err = security_secmark_relabel_packet(tmp_secid);
>> +       /* Using le[0] is scaffolding */
>> +       err = security_secmark_relabel_packet(blob.secid[0]);
>>         if (err)
>>                 return err;
> At the very least it looks like the comment above needs an update.

I can see that. 

> However, I would really like to see an explanation in this patch,
> either in the comments or in the commit description, about how you
> plan to handle secmarks.

Yes. It should probably be spread between here, 0017 and the introduction.

>   If your plan is to always have it be the
> first LSM, let's admit that and document it appropriately.  If there
> is something much grander coming later in the patchset I guess
> "scaffolding" is an okay term, but it would be good to mention in the
> commit description that this will be replaced with something better
> later in the patchset.

You are correct.

> I'm worried about the case five years from know when we are changing
> this code, either due to bugs or new features, and we stumble across
> this commit.  Was it always intended to be this way?  Or was this
> temporary?  Right now I don't know.
>
>> -       priv->secid = tmp_secid;
>> +       /* Using le[0] is scaffolding */
>> +       priv->secid = blob.secid[0];
>>         return 0;
>>  }
> ...
>
>> diff --git a/net/netlabel/netlabel_unlabeled.c b/net/netlabel/netlabel_unlabeled.c
>> index d2e4ab8d1cb1..7a5a87f15736 100644
>> --- a/net/netlabel/netlabel_unlabeled.c
>> +++ b/net/netlabel/netlabel_unlabeled.c
>> @@ -881,7 +881,7 @@ static int netlbl_unlabel_staticadd(struct sk_buff *skb,
>>         void *addr;
>>         void *mask;
>>         u32 addr_len;
>> -       u32 secid;
>> +       struct lsmblob blob;
>>         struct netlbl_audit audit_info;
>>
>>         /* Don't allow users to add both IPv4 and IPv6 addresses for a
>> @@ -905,12 +905,13 @@ static int netlbl_unlabel_staticadd(struct sk_buff *skb,
>>         ret_val = security_secctx_to_secid(
>>                                   nla_data(info->attrs[NLBL_UNLABEL_A_SECCTX]),
>>                                   nla_len(info->attrs[NLBL_UNLABEL_A_SECCTX]),
>> -                                 &secid);
>> +                                 &blob);
>>         if (ret_val != 0)
>>                 return ret_val;
>>
>> +       /* scaffolding with the [0] */
>>         return netlbl_unlhsh_add(&init_net,
>> -                                dev_name, addr, mask, addr_len, secid,
>> +                                dev_name, addr, mask, addr_len, blob.secid[0],
>>                                  &audit_info);
>>  }
> Same as above, although this time with the peer label.
>