LSM: generalize flag passing to security_capable

This patch provides a general mechanism for passing flags to the
security_capable LSM hook. It replaces the specific 'audit' flag that is
used to tell security_capable whether it should log an audit message for
the given capability check. The reason for generalizing this flag
passing is so we can add an additional flag that signifies whether
security_capable is being called by a setid syscall (which is needed by
the proposed SafeSetID LSM).

Signed-off-by: Micah Morton <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: James Morris <[e-mail]>

include/linux/lsm_hooks.h

···
  *	@cred contains the credentials to use.
  *	@ns contains the user namespace we want the capability in
  *	@cap contains the capability <include/linux/capability.h>.
- *	@audit contains whether to write an audit message or not
+ *	@opts contains options for the capable check <include/linux/security.h>
  *	Return 0 if the capability is granted for @tsk.
  * @syslog:
  *	Check permission before accessing the kernel message ring or changing
···
 			const kernel_cap_t *effective,
 			const kernel_cap_t *inheritable,
 			const kernel_cap_t *permitted);
-	int (*capable)(const struct cred *cred, struct user_namespace *ns,
-			int cap, int audit);
+	int (*capable)(const struct cred *cred,
+			struct user_namespace *ns,
+			int cap,
+			unsigned int opts);
 	int (*quotactl)(int cmds, int type, int id, struct super_block *sb);
 	int (*quota_on)(struct dentry *dentry);
 	int (*syslog)(int type);

include/linux/security.h

···
 struct xfrm_sec_ctx;
 struct mm_struct;
 
+/* Default (no) options for the capable function */
+#define CAP_OPT_NONE 0x0
 /* If capable should audit the security request */
-#define SECURITY_CAP_NOAUDIT 0
-#define SECURITY_CAP_AUDIT 1
+#define CAP_OPT_NOAUDIT BIT(1)
+/* If capable is being called by a setid function */
+#define CAP_OPT_INSETID BIT(2)
 
 /* LSM Agnostic defines for sb_set_mnt_opts */
 #define SECURITY_LSM_NATIVE_LABELS	1
···
 
 /* These functions are in security/commoncap.c */
 extern int cap_capable(const struct cred *cred, struct user_namespace *ns,
-		       int cap, int audit);
+		       int cap, unsigned int opts);
 extern int cap_settime(const struct timespec64 *ts, const struct timezone *tz);
 extern int cap_ptrace_access_check(struct task_struct *child, unsigned int mode);
 extern int cap_ptrace_traceme(struct task_struct *parent);
···
 		    const kernel_cap_t *effective,
 		    const kernel_cap_t *inheritable,
 		    const kernel_cap_t *permitted);
-int security_capable(const struct cred *cred, struct user_namespace *ns,
-			int cap);
-int security_capable_noaudit(const struct cred *cred, struct user_namespace *ns,
-			     int cap);
+int security_capable(const struct cred *cred,
+		       struct user_namespace *ns,
+		       int cap,
+		       unsigned int opts);
 int security_quotactl(int cmds, int type, int id, struct super_block *sb);
 int security_quota_on(struct dentry *dentry);
 int security_syslog(int type);
···
 }
 
 static inline int security_capable(const struct cred *cred,
-				   struct user_namespace *ns, int cap)
+				   struct user_namespace *ns,
+				   int cap,
+				   unsigned int opts)
 {
-	return cap_capable(cred, ns, cap, SECURITY_CAP_AUDIT);
-}
-
-static inline int security_capable_noaudit(const struct cred *cred,
-					   struct user_namespace *ns, int cap) {
-	return cap_capable(cred, ns, cap, SECURITY_CAP_NOAUDIT);
+	return cap_capable(cred, ns, cap, opts);
 }
 
 static inline int security_quotactl(int cmds, int type, int id,

kernel/capability.c

···
 	int ret;
 
 	rcu_read_lock();
-	ret = security_capable(__task_cred(t), ns, cap);
+	ret = security_capable(__task_cred(t), ns, cap, CAP_OPT_NONE);
 	rcu_read_unlock();
 
 	return (ret == 0);
···
 	int ret;
 
 	rcu_read_lock();
-	ret = security_capable_noaudit(__task_cred(t), ns, cap);
+	ret = security_capable(__task_cred(t), ns, cap, CAP_OPT_NOAUDIT);
 	rcu_read_unlock();
 
 	return (ret == 0);
···
 	return has_ns_capability_noaudit(t, &init_user_ns, cap);
 }
 
-static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
+static bool ns_capable_common(struct user_namespace *ns,
+			      int cap,
+			      unsigned int opts)
 {
 	int capable;
 
···
 		BUG();
 	}
 
-	capable = audit ? security_capable(current_cred(), ns, cap) :
-			  security_capable_noaudit(current_cred(), ns, cap);
+	capable = security_capable(current_cred(), ns, cap, opts);
 	if (capable == 0) {
 		current->flags |= PF_SUPERPRIV;
 		return true;
···
  */
 bool ns_capable(struct user_namespace *ns, int cap)
 {
-	return ns_capable_common(ns, cap, true);
+	return ns_capable_common(ns, cap, CAP_OPT_NONE);
 }
 EXPORT_SYMBOL(ns_capable);
 
···
  */
 bool ns_capable_noaudit(struct user_namespace *ns, int cap)
 {
-	return ns_capable_common(ns, cap, false);
+	return ns_capable_common(ns, cap, CAP_OPT_NOAUDIT);
 }
 EXPORT_SYMBOL(ns_capable_noaudit);
 
···
 bool file_ns_capable(const struct file *file, struct user_namespace *ns,
 		     int cap)
 {
+
 	if (WARN_ON_ONCE(!cap_valid(cap)))
 		return false;
 
-	if (security_capable(file->f_cred, ns, cap) == 0)
+	if (security_capable(file->f_cred, ns, cap, CAP_OPT_NONE) == 0)
 		return true;
 
 	return false;
···
 {
 	int ret = 0;  /* An absent tracer adds no restrictions */
 	const struct cred *cred;
+
 	rcu_read_lock();
 	cred = rcu_dereference(tsk->ptracer_cred);
 	if (cred)
-		ret = security_capable_noaudit(cred, ns, CAP_SYS_PTRACE);
+		ret = security_capable(cred, ns, CAP_SYS_PTRACE,
+				       CAP_OPT_NOAUDIT);
 	rcu_read_unlock();
 	return (ret == 0);
 }

kernel/seccomp.c

···
 	 * behavior of privileged children.
 	 */
 	if (!task_no_new_privs(current) &&
-	    security_capable_noaudit(current_cred(), current_user_ns(),
-				     CAP_SYS_ADMIN) != 0)
+	    security_capable(current_cred(), current_user_ns(),
+				     CAP_SYS_ADMIN, CAP_OPT_NOAUDIT) != 0)
 		return ERR_PTR(-EACCES);
 
 	/* Allocate a new seccomp_filter */

security/apparmor/capability.c

···
  * profile_capable - test if profile allows use of capability @cap
  * @profile: profile being enforced    (NOT NULL, NOT unconfined)
  * @cap: capability to test if allowed
- * @audit: whether an audit record should be generated
+ * @opts: CAP_OPT_NOAUDIT bit determines whether audit record is generated
  * @sa: audit data (MAY BE NULL indicating no auditing)
  *
  * Returns: 0 if allowed else -EPERM
  */
-static int profile_capable(struct aa_profile *profile, int cap, int audit,
-			   struct common_audit_data *sa)
+static int profile_capable(struct aa_profile *profile, int cap,
+			   unsigned int opts, struct common_audit_data *sa)
 {
 	int error;
 
···
 	else
 		error = -EPERM;
 
-	if (audit == SECURITY_CAP_NOAUDIT) {
+	if (opts & CAP_OPT_NOAUDIT) {
 		if (!COMPLAIN_MODE(profile))
 			return error;
 		/* audit the cap request in complain mode but note that it
···
  * aa_capable - test permission to use capability
  * @label: label being tested for capability (NOT NULL)
  * @cap: capability to be tested
- * @audit: whether an audit record should be generated
+ * @opts: CAP_OPT_NOAUDIT bit determines whether audit record is generated
  *
  * Look up capability in profile capability set.
  *
  * Returns: 0 on success, or else an error code.
  */
-int aa_capable(struct aa_label *label, int cap, int audit)
+int aa_capable(struct aa_label *label, int cap, unsigned int opts)
 {
 	struct aa_profile *profile;
 	int error = 0;
···
 
 	sa.u.cap = cap;
 	error = fn_for_each_confined(label, profile,
-			profile_capable(profile, cap, audit, &sa));
+			profile_capable(profile, cap, opts, &sa));
 
 	return error;
 }

security/apparmor/include/capability.h

···
 
 extern struct aa_sfs_entry aa_sfs_entry_caps[];
 
-int aa_capable(struct aa_label *label, int cap, int audit);
+int aa_capable(struct aa_label *label, int cap, unsigned int opts);
 
 static inline void aa_free_cap_rules(struct aa_caps *caps)
 {

security/apparmor/ipc.c

···
 	aad(sa)->label = &tracer->label;
 	aad(sa)->peer = tracee;
 	aad(sa)->request = 0;
-	aad(sa)->error = aa_capable(&tracer->label, CAP_SYS_PTRACE, 1);
+	aad(sa)->error = aa_capable(&tracer->label, CAP_SYS_PTRACE,
+				    CAP_OPT_NONE);
 
 	return aa_audit(AUDIT_APPARMOR_AUTO, tracer, sa, audit_ptrace_cb);
 }

security/apparmor/lsm.c

···
 }
 
 static int apparmor_capable(const struct cred *cred, struct user_namespace *ns,
-			    int cap, int audit)
+			    int cap, unsigned int opts)
 {
 	struct aa_label *label;
 	int error = 0;
 
 	label = aa_get_newest_cred_label(cred);
 	if (!unconfined(label))
-		error = aa_capable(label, cap, audit);
+		error = aa_capable(label, cap, opts);
 	aa_put_label(label);
 
 	return error;

security/apparmor/resource.c

···
 	 */
 
 	if (label != peer &&
-	    aa_capable(label, CAP_SYS_RESOURCE, SECURITY_CAP_NOAUDIT) != 0)
+	    aa_capable(label, CAP_SYS_RESOURCE, CAP_OPT_NOAUDIT) != 0)
 		error = fn_for_each(label, profile,
 				audit_resource(profile, resource,
 					       new_rlim->rlim_max, peer,

security/commoncap.c

···
  * kernel's capable() and has_capability() returns 1 for this case.
  */
 int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
-		int cap, int audit)
+		int cap, unsigned int opts)
 {
 	struct user_namespace *ns = targ_ns;
 
···
  */
 static inline int cap_inh_is_capped(void)
 {
-
 	/* they are so limited unless the current task has the CAP_SETPCAP
 	 * capability
 	 */
 	if (cap_capable(current_cred(), current_cred()->user_ns,
-			CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0)
+			CAP_SETPCAP, CAP_OPT_NONE) == 0)
 		return 0;
 	return 1;
 }
···
 		    || ((old->securebits & SECURE_ALL_LOCKS & ~arg2))	/*[2]*/
 		    || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS))	/*[3]*/
 		    || (cap_capable(current_cred(),
-				    current_cred()->user_ns, CAP_SETPCAP,
-				    SECURITY_CAP_AUDIT) != 0)		/*[4]*/
+				    current_cred()->user_ns,
+				    CAP_SETPCAP,
+				    CAP_OPT_NONE) != 0)			/*[4]*/
 			/*
 			 * [1] no changing of bits that are locked
 			 * [2] no unlocking of locks
···
 {
 	int cap_sys_admin = 0;
 
-	if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
-			SECURITY_CAP_NOAUDIT) == 0)
+	if (cap_capable(current_cred(), &init_user_ns,
+				CAP_SYS_ADMIN, CAP_OPT_NOAUDIT) == 0)
 		cap_sys_admin = 1;
+
 	return cap_sys_admin;
 }
 
···
 
 	if (addr < dac_mmap_min_addr) {
 		ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
-				  SECURITY_CAP_AUDIT);
+				  CAP_OPT_NONE);
 		/* set PF_SUPERPRIV if it turns out we allow the low mmap */
 		if (ret == 0)
 			current->flags |= PF_SUPERPRIV;

security/security.c

···
 				effective, inheritable, permitted);
 }
 
-int security_capable(const struct cred *cred, struct user_namespace *ns,
-		     int cap)
+int security_capable(const struct cred *cred,
+		     struct user_namespace *ns,
+		     int cap,
+		     unsigned int opts)
 {
-	return call_int_hook(capable, 0, cred, ns, cap, SECURITY_CAP_AUDIT);
-}
-
-int security_capable_noaudit(const struct cred *cred, struct user_namespace *ns,
-			     int cap)
-{
-	return call_int_hook(capable, 0, cred, ns, cap, SECURITY_CAP_NOAUDIT);
+	return call_int_hook(capable, 0, cred, ns, cap, opts);
 }
 
 int security_quotactl(int cmds, int type, int id, struct super_block *sb)

security/selinux/hooks.c

···
 
 /* Check whether a task is allowed to use a capability. */
 static int cred_has_capability(const struct cred *cred,
-			       int cap, int audit, bool initns)
+			       int cap, unsigned int opts, bool initns)
 {
 	struct common_audit_data ad;
 	struct av_decision avd;
···
 
 	rc = avc_has_perm_noaudit(&selinux_state,
 				  sid, sid, sclass, av, 0, &avd);
-	if (audit == SECURITY_CAP_AUDIT) {
+	if (!(opts & CAP_OPT_NOAUDIT)) {
 		int rc2 = avc_audit(&selinux_state,
 				    sid, sid, sclass, av, &avd, rc, &ad, 0);
 		if (rc2)
···
  */
 
 static int selinux_capable(const struct cred *cred, struct user_namespace *ns,
-			   int cap, int audit)
+			   int cap, unsigned int opts)
 {
-	return cred_has_capability(cred, cap, audit, ns == &init_user_ns);
+	return cred_has_capability(cred, cap, opts, ns == &init_user_ns);
 }
 
 static int selinux_quotactl(int cmds, int type, int id, struct super_block *sb)
···
 	int rc, cap_sys_admin = 0;
 
 	rc = cred_has_capability(current_cred(), CAP_SYS_ADMIN,
-				 SECURITY_CAP_NOAUDIT, true);
+				 CAP_OPT_NOAUDIT, true);
 	if (rc == 0)
 		cap_sys_admin = 1;
 
···
 static bool has_cap_mac_admin(bool audit)
 {
 	const struct cred *cred = current_cred();
-	int cap_audit = audit ? SECURITY_CAP_AUDIT : SECURITY_CAP_NOAUDIT;
+	unsigned int opts = audit ? CAP_OPT_NONE : CAP_OPT_NOAUDIT;
 
-	if (cap_capable(cred, &init_user_ns, CAP_MAC_ADMIN, cap_audit))
+	if (cap_capable(cred, &init_user_ns, CAP_MAC_ADMIN, opts))
 		return false;
-	if (cred_has_capability(cred, CAP_MAC_ADMIN, cap_audit, true))
+	if (cred_has_capability(cred, CAP_MAC_ADMIN, opts, true))
 		return false;
 	return true;
 }
···
 	case KDSKBENT:
 	case KDSKBSENT:
 		error = cred_has_capability(cred, CAP_SYS_TTY_CONFIG,
-					    SECURITY_CAP_AUDIT, true);
+					    CAP_OPT_NONE, true);
 		break;
 
 	/* default case assumes that the command will go

security/smack/smack_access.c

···
 	struct smack_known_list_elem *sklep;
 	int rc;
 
-	rc = cap_capable(cred, &init_user_ns, cap, SECURITY_CAP_AUDIT);
+	rc = cap_capable(cred, &init_user_ns, cap, CAP_OPT_NONE);
 	if (rc)
 		return false;