linux-kernel - Re: [PATCH v23 02/23] LSM: Create and manage the lsmblob data structure.

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Date:   Mon, 28 Dec 2020 14:24:34 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        casey.schaufler@...el.com, jmorris@...ei.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org
Cc:     linux-audit@...hat.com, keescook@...omium.org,
        john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
        paul@...l-moore.com, sds@...ho.nsa.gov,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v23 02/23] LSM: Create and manage the lsmblob data
 structure.

Hi Casey,

On Fri, 2020-11-20 at 12:14 -0800, Casey Schaufler wrote:
> diff --git a/security/security.c b/security/security.c
> index 5da8b3643680..d01363cb0082 100644
> --- a/security/security.c
> +++ b/security/security.c
> 
> @@ -2510,7 +2526,24 @@ int security_key_getsecurity(struct key *key, char **_buffer)
> 
>  int security_audit_rule_init(u32 field, u32 op, char *rulestr, void **lsmrule)
>  {
> -       return call_int_hook(audit_rule_init, 0, field, op, rulestr, lsmrule);
> +       struct security_hook_list *hp;
> +       bool one_is_good = false;
> +       int rc = 0;
> +       int trc;
> +
> +       hlist_for_each_entry(hp, &security_hook_heads.audit_rule_init, list) {
> +               if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot))
> +                       continue;
> +               trc = hp->hook.audit_rule_init(field, op, rulestr,
> +                                              &lsmrule[hp->lsmid->slot]);
> +               if (trc == 0)
> +                       one_is_good = true;
> +               else
> +                       rc = trc;
> +       }
> +       if (one_is_good)
> +               return 0;
> +       return rc;
>  }

So the same string may be defined by multiple LSMs.
> 
>  int security_audit_rule_known(struct audit_krule *krule)
> @@ -2518,14 +2551,31 @@ int security_audit_rule_known(struct audit_krule *krule)
>         return call_int_hook(audit_rule_known, 0, krule);
>  }
> 
> -void security_audit_rule_free(void *lsmrule)
> +void security_audit_rule_free(void **lsmrule)
>  {
> -       call_void_hook(audit_rule_free, lsmrule);
> +       struct security_hook_list *hp;
> +
> +       hlist_for_each_entry(hp, &security_hook_heads.audit_rule_free, list) {
> +               if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot))
> +                       continue;
> +               hp->hook.audit_rule_free(lsmrule[hp->lsmid->slot]);
> +       }
>  }
> 

If one LSM frees the string, then the string is deleted from all LSMs. 
I don't understand how this safe.

> -int security_audit_rule_match(u32 secid, u32 field, u32 op, void *lsmrule)
> +int security_audit_rule_match(u32 secid, u32 field, u32 op, void **lsmrule)
>  {
> -       return call_int_hook(audit_rule_match, 0, secid, field, op, lsmrule);
> +       struct security_hook_list *hp;
> +       int rc;
> +
> +       hlist_for_each_entry(hp, &security_hook_heads.audit_rule_match, list) {
> +               if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot))
> +                       continue;
> +               rc = hp->hook.audit_rule_match(secid, field, op,
> +                                              &lsmrule[hp->lsmid->slot]);
> +               if (rc)
> +                       return rc;

Suppose that there is an IMA dont_measure or dont_appraise rule, if one
LSM matches, then this returns true, causing any measurement or
integrity verification to be skipped.  

Sample policy rules:
dont_measure obj_type=foo_log
dont_appraise obj_type=foo_log

Are there any plans to prevent label collisions or at least notify of a
label collision?

Mimi

> +       }
> +       return 0;
>  }
>  #endif /* CONFIG_AUDIT */