linux-kernel - Re: [PATCH 01/10] capability: introduce new capable flag CAP_OPT_NOAUDIT

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Message-ID: <4cfca86d-ceb7-4abe-8b6b-35194fc55565@canonical.com>
Date: Mon, 10 Jun 2024 14:12:01 -0700
From: John Johansen <john.johansen@...onical.com>
To: Christian Göttsche <cgzones@...glemail.com>,
 linux-security-module@...r.kernel.org
Cc: linux-block@...r.kernel.org, Paul Moore <paul@...l-moore.com>,
 James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>,
 Stephen Smalley <stephen.smalley.work@...il.com>,
 Ondrej Mosnacek <omosnace@...hat.com>,
 Casey Schaufler <casey@...aufler-ca.com>,
 Christian Brauner <brauner@...nel.org>,
 Roberto Sassu <roberto.sassu@...wei.com>, Mimi Zohar <zohar@...ux.ibm.com>,
 Khadija Kamran <kamrankhadijadj@...il.com>,
 Andrii Nakryiko <andrii@...nel.org>, linux-kernel@...r.kernel.org,
 apparmor@...ts.ubuntu.com, selinux@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH 01/10] capability: introduce new capable flag
 CAP_OPT_NOAUDIT_ONDENY

On 3/15/24 04:37, Christian Göttsche wrote:
> Introduce a new capable flag, CAP_OPT_NOAUDIT_ONDENY, to not generate
> an audit event if the requested capability is not granted.  This will be
> used in a new capable_any() functionality to reduce the number of
> necessary capable calls.
> 
> Handle the flag accordingly in AppArmor and SELinux.
> 
> CC: linux-block@...r.kernel.org
> Suggested-by: Paul Moore <paul@...l-moore.com>
> Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
Acked-by: John Johansen <john.johansen@...onical.com>

> ---
> v5:
>     rename flag to CAP_OPT_NOAUDIT_ONDENY, suggested by Serge:
>       https://lore.kernel.org/all/20230606190013.GA640488@mail.hallyn.com/
> ---
>   include/linux/security.h       |  2 ++
>   security/apparmor/capability.c |  8 +++++---
>   security/selinux/hooks.c       | 14 ++++++++------
>   3 files changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 41a8f667bdfa..c60cae78ff8b 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -70,6 +70,8 @@ struct lsm_ctx;
>   #define CAP_OPT_NOAUDIT BIT(1)
>   /* If capable is being called by a setid function */
>   #define CAP_OPT_INSETID BIT(2)
> +/* If capable should audit the security request for authorized requests only */
> +#define CAP_OPT_NOAUDIT_ONDENY BIT(3)
>   
>   /* LSM Agnostic defines for security_sb_set_mnt_opts() flags */
>   #define SECURITY_LSM_NATIVE_LABELS	1
> diff --git a/security/apparmor/capability.c b/security/apparmor/capability.c
> index 9934df16c843..08c9c9a0fc19 100644
> --- a/security/apparmor/capability.c
> +++ b/security/apparmor/capability.c
> @@ -108,7 +108,8 @@ static int audit_caps(struct apparmor_audit_data *ad, struct aa_profile *profile
>    * profile_capable - test if profile allows use of capability @cap
>    * @profile: profile being enforced    (NOT NULL, NOT unconfined)
>    * @cap: capability to test if allowed
> - * @opts: CAP_OPT_NOAUDIT bit determines whether audit record is generated
> + * @opts: CAP_OPT_NOAUDIT/CAP_OPT_NOAUDIT_ONDENY bit determines whether audit
> + *	record is generated
>    * @ad: audit data (MAY BE NULL indicating no auditing)
>    *
>    * Returns: 0 if allowed else -EPERM
> @@ -126,7 +127,7 @@ static int profile_capable(struct aa_profile *profile, int cap,
>   	else
>   		error = -EPERM;
>   
> -	if (opts & CAP_OPT_NOAUDIT) {
> +	if ((opts & CAP_OPT_NOAUDIT) || ((opts & CAP_OPT_NOAUDIT_ONDENY) && error)) {
>   		if (!COMPLAIN_MODE(profile))
>   			return error;
>   		/* audit the cap request in complain mode but note that it
> @@ -143,7 +144,8 @@ static int profile_capable(struct aa_profile *profile, int cap,
>    * @subj_cred: cred we are testing capability against
>    * @label: label being tested for capability (NOT NULL)
>    * @cap: capability to be tested
> - * @opts: CAP_OPT_NOAUDIT bit determines whether audit record is generated
> + * @opts: CAP_OPT_NOAUDIT/CAP_OPT_NOAUDIT_ONDENY bit determines whether audit
> + *	record is generated
>    *
>    * Look up capability in profile capability set.
>    *
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 3448454c82d0..1a2c7c1a89be 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -1624,7 +1624,7 @@ static int cred_has_capability(const struct cred *cred,
>   	u16 sclass;
>   	u32 sid = cred_sid(cred);
>   	u32 av = CAP_TO_MASK(cap);
> -	int rc;
> +	int rc, rc2;
>   
>   	ad.type = LSM_AUDIT_DATA_CAP;
>   	ad.u.cap = cap;
> @@ -1643,11 +1643,13 @@ static int cred_has_capability(const struct cred *cred,
>   	}
>   
>   	rc = avc_has_perm_noaudit(sid, sid, sclass, av, 0, &avd);
> -	if (!(opts & CAP_OPT_NOAUDIT)) {
> -		int rc2 = avc_audit(sid, sid, sclass, av, &avd, rc, &ad);
> -		if (rc2)
> -			return rc2;
> -	}
> +	if ((opts & CAP_OPT_NOAUDIT) || ((opts & CAP_OPT_NOAUDIT_ONDENY) && rc))
> +		return rc;
> +
> +	rc2 = avc_audit(sid, sid, sclass, av, &avd, rc, &ad);
> +	if (rc2)
> +		return rc2;
> +
>   	return rc;
>   }
>