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 <mortonm@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.morris@microsoft.com>

2 files changed, 19 insertions, 17 deletions

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 40511a8a5ae6..195707210975 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1270,7 +1270,7 @@
  *	@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
@@ -1446,8 +1446,10 @@ union security_list_options {
 			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);
diff --git a/include/linux/security.h b/include/linux/security.h
index b2c5333ed4b5..13537a49ae97 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -54,9 +54,12 @@ struct xattr;
 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
@@ -72,7 +75,7 @@ enum lsm_event {
 
 /* 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);
@@ -207,10 +210,10 @@ int security_capset(struct cred *new, const struct cred *old,
 		    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);
@@ -464,14 +467,11 @@ static inline int security_capset(struct cred *new,
 }
 
 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,