linux-kernel - Re: [PATCH v3 04/15] selinux: Refactor to remove bprm

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Date:   Wed, 19 Jul 2017 20:19:35 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Kees Cook <keescook@...omium.org>,
        Stephen Smalley <sds@...ho.nsa.gov>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        John Johansen <john.johansen@...onical.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        James Morris <james.l.morris@...cle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 04/15] selinux: Refactor to remove bprm_secureexec hook

On Wed, Jul 19, 2017 at 8:03 PM, Paul Moore <paul@...l-moore.com> wrote:
> On Tue, Jul 18, 2017 at 6:25 PM, Kees Cook <keescook@...omium.org> wrote:
>> The SELinux bprm_secureexec hook can be merged with the bprm_set_creds
>> hook since it's dealing with the same information, and all of the details
>> are finalized during the first call to the bprm_set_creds hook via
>> prepare_binprm() (subsequent calls due to binfmt_script, etc, are ignored
>> via bprm->called_set_creds).
>>
>> Here, the test can just happen at the end of the bprm_set_creds hook,
>> and the bprm_secureexec hook can be dropped.
>>
>> Cc: Paul Moore <paul@...l-moore.com>
>> Cc: Stephen Smalley <sds@...ho.nsa.gov>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  security/selinux/hooks.c | 24 +++++-------------------
>>  1 file changed, 5 insertions(+), 19 deletions(-)
>
> This seems reasonable in the context of the other changes.
>
> Stephen just posted an AT_SECURE test for the selinux-testsuite on the
> SELinux mailing list, it would be nice to ensure that this patchset
> doesn't run afoul of that.

Quick follow-up: I just merged Stephen's test into the test suite:

* https://github.com/SELinuxProject/selinux-testsuite

> Acked-by: Paul Moore <paul@...l-moore.com>
>
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index 0f1450a06b02..18038f73a2f7 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -2413,30 +2413,17 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm)
>>
>>                 /* Clear any possibly unsafe personality bits on exec: */
>>                 bprm->per_clear |= PER_CLEAR_ON_SETID;
>> -       }
>> -
>> -       return 0;
>> -}
>> -
>> -static int selinux_bprm_secureexec(struct linux_binprm *bprm)
>> -{
>> -       const struct task_security_struct *tsec = current_security();
>> -       u32 sid, osid;
>> -       int atsecure = 0;
>> -
>> -       sid = tsec->sid;
>> -       osid = tsec->osid;
>>
>> -       if (osid != sid) {
>>                 /* Enable secure mode for SIDs transitions unless
>>                    the noatsecure permission is granted between
>>                    the two SIDs, i.e. ahp returns 0. */
>> -               atsecure = avc_has_perm(osid, sid,
>> -                                       SECCLASS_PROCESS,
>> -                                       PROCESS__NOATSECURE, NULL);
>> +               rc = avc_has_perm(old_tsec->sid, new_tsec->sid,
>> +                                 SECCLASS_PROCESS, PROCESS__NOATSECURE,
>> +                                 NULL);
>> +               bprm->secureexec |= !!rc;
>>         }
>>
>> -       return !!atsecure;
>> +       return 0;
>>  }
>>
>>  static int match_file(const void *p, struct file *file, unsigned fd)
>> @@ -6151,7 +6138,6 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
>>         LSM_HOOK_INIT(bprm_set_creds, selinux_bprm_set_creds),
>>         LSM_HOOK_INIT(bprm_committing_creds, selinux_bprm_committing_creds),
>>         LSM_HOOK_INIT(bprm_committed_creds, selinux_bprm_committed_creds),
>> -       LSM_HOOK_INIT(bprm_secureexec, selinux_bprm_secureexec),
>>
>>         LSM_HOOK_INIT(sb_alloc_security, selinux_sb_alloc_security),
>>         LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
>> --
>> 2.7.4
>
> --
> paul moore
> www.paul-moore.com



-- 
paul moore
www.paul-moore.com