keys: Make the KEY_NEED_* perms an enum rather than a mask

Since the meaning of combining the KEY_NEED_* constants is undefined, make
it so that you can't do that by turning them into an enum.

The enum is also given some extra values to represent special
circumstances, such as:

 (1) The '0' value is reserved and causes a warning to trap the parameter
     being unset.

 (2) The key is to be unlinked and we require no permissions on it, only
     the keyring, (this replaces the KEY_LOOKUP_FOR_UNLINK flag).

 (3) An override due to CAP_SYS_ADMIN.

 (4) An override due to an instantiation token being present.

 (5) The permissions check is being deferred to later key_permission()
     calls.

The extra values give the opportunity for LSMs to audit these situations.

[Note: This really needs overhauling so that lookup_user_key() tells
 key_task_permission() and the LSM what operation is being done and leaves
 it to those functions to decide how to map that onto the available
 permits.  However, I don't really want to make these change in the middle
 of the notifications patchset.]

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
cc: Paul Moore <paul@paul-moore.com>
cc: Stephen Smalley <stephen.smalley.work@gmail.com>
cc: Casey Schaufler <casey@schaufler-ca.com>
cc: keyrings@vger.kernel.org
cc: selinux@vger.kernel.org

4 files changed, 59 insertions, 42 deletions

diff --git a/security/keys/internal.h b/security/keys/internal.h
index 28e17f4f3328..1fc17cb317a9 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -167,7 +167,6 @@ extern bool lookup_user_key_possessed(const struct key *key,
 				      const struct key_match_data *match_data);
 #define KEY_LOOKUP_CREATE	0x01
 #define KEY_LOOKUP_PARTIAL	0x02
-#define KEY_LOOKUP_FOR_UNLINK	0x04
 
 extern long join_session_keyring(const char *name);
 extern void key_change_session_keyring(struct callback_head *twork);
@@ -183,7 +182,7 @@ extern void key_gc_keytype(struct key_type *ktype);
 
 extern int key_task_permission(const key_ref_t key_ref,
 			       const struct cred *cred,
-			       key_perm_t perm);
+			       enum key_need_perm need_perm);
 
 static inline void notify_key(struct key *key,
 			      enum key_notification_subtype subtype, u32 aux)
@@ -205,9 +204,10 @@ static inline void notify_key(struct key *key,
 /*
  * Check to see whether permission is granted to use a key in the desired way.
  */
-static inline int key_permission(const key_ref_t key_ref, unsigned perm)
+static inline int key_permission(const key_ref_t key_ref,
+				 enum key_need_perm need_perm)
 {
-	return key_task_permission(key_ref, current_cred(), perm);
+	return key_task_permission(key_ref, current_cred(), need_perm);
 }
 
 extern struct key_type key_type_request_key_auth;
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 7d8de1c9a478..6763ee45e04d 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -434,7 +434,7 @@ long keyctl_invalidate_key(key_serial_t id)
 
 		/* Root is permitted to invalidate certain special keys */
 		if (capable(CAP_SYS_ADMIN)) {
-			key_ref = lookup_user_key(id, 0, 0);
+			key_ref = lookup_user_key(id, 0, KEY_SYSADMIN_OVERRIDE);
 			if (IS_ERR(key_ref))
 				goto error;
 			if (test_bit(KEY_FLAG_ROOT_CAN_INVAL,
@@ -479,7 +479,8 @@ long keyctl_keyring_clear(key_serial_t ringid)
 
 		/* Root is permitted to invalidate certain special keyrings */
 		if (capable(CAP_SYS_ADMIN)) {
-			keyring_ref = lookup_user_key(ringid, 0, 0);
+			keyring_ref = lookup_user_key(ringid, 0,
+						      KEY_SYSADMIN_OVERRIDE);
 			if (IS_ERR(keyring_ref))
 				goto error;
 			if (test_bit(KEY_FLAG_ROOT_CAN_CLEAR,
@@ -563,7 +564,7 @@ long keyctl_keyring_unlink(key_serial_t id, key_serial_t ringid)
 		goto error;
 	}
 
-	key_ref = lookup_user_key(id, KEY_LOOKUP_FOR_UNLINK, 0);
+	key_ref = lookup_user_key(id, KEY_LOOKUP_PARTIAL, KEY_NEED_UNLINK);
 	if (IS_ERR(key_ref)) {
 		ret = PTR_ERR(key_ref);
 		goto error2;
@@ -663,7 +664,7 @@ long keyctl_describe_key(key_serial_t keyid,
 				key_put(instkey);
 				key_ref = lookup_user_key(keyid,
 							  KEY_LOOKUP_PARTIAL,
-							  0);
+							  KEY_AUTHTOKEN_OVERRIDE);
 				if (!IS_ERR(key_ref))
 					goto okay;
 			}
@@ -833,7 +834,7 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 	size_t key_data_len;
 
 	/* find the key first */
-	key_ref = lookup_user_key(keyid, 0, 0);
+	key_ref = lookup_user_key(keyid, 0, KEY_DEFER_PERM_CHECK);
 	if (IS_ERR(key_ref)) {
 		ret = -ENOKEY;
 		goto out;
@@ -1471,7 +1472,7 @@ long keyctl_set_timeout(key_serial_t id, unsigned timeout)
 				key_put(instkey);
 				key_ref = lookup_user_key(id,
 							  KEY_LOOKUP_PARTIAL,
-							  0);
+							  KEY_AUTHTOKEN_OVERRIDE);
 				if (!IS_ERR(key_ref))
 					goto okay;
 			}
@@ -1579,7 +1580,8 @@ long keyctl_get_security(key_serial_t keyid,
 			return PTR_ERR(instkey);
 		key_put(instkey);
 
-		key_ref = lookup_user_key(keyid, KEY_LOOKUP_PARTIAL, 0);
+		key_ref = lookup_user_key(keyid, KEY_LOOKUP_PARTIAL,
+					  KEY_AUTHTOKEN_OVERRIDE);
 		if (IS_ERR(key_ref))
 			return PTR_ERR(key_ref);
 	}
diff --git a/security/keys/permission.c b/security/keys/permission.c
index 085f907b64ac..4a61f804e80f 100644
--- a/security/keys/permission.c
+++ b/security/keys/permission.c
@@ -13,7 +13,7 @@
  * key_task_permission - Check a key can be used
  * @key_ref: The key to check.
  * @cred: The credentials to use.
- * @perm: The permissions to check for.
+ * @need_perm: The permission required.
  *
  * Check to see whether permission is granted to use a key in the desired way,
  * but permit the security modules to override.
@@ -24,12 +24,30 @@
  * permissions bits or the LSM check.
  */
 int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
-			unsigned perm)
+			enum key_need_perm need_perm)
 {
 	struct key *key;
-	key_perm_t kperm;
+	key_perm_t kperm, mask;
 	int ret;
 
+	switch (need_perm) {
+	default:
+		WARN_ON(1);
+		return -EACCES;
+	case KEY_NEED_UNLINK:
+	case KEY_SYSADMIN_OVERRIDE:
+	case KEY_AUTHTOKEN_OVERRIDE:
+	case KEY_DEFER_PERM_CHECK:
+		goto lsm;
+
+	case KEY_NEED_VIEW:	mask = KEY_OTH_VIEW;	break;
+	case KEY_NEED_READ:	mask = KEY_OTH_READ;	break;
+	case KEY_NEED_WRITE:	mask = KEY_OTH_WRITE;	break;
+	case KEY_NEED_SEARCH:	mask = KEY_OTH_SEARCH;	break;
+	case KEY_NEED_LINK:	mask = KEY_OTH_LINK;	break;
+	case KEY_NEED_SETATTR:	mask = KEY_OTH_SETATTR;	break;
+	}
+
 	key = key_ref_to_ptr(key_ref);
 
 	/* use the second 8-bits of permissions for keys the caller owns */
@@ -64,13 +82,12 @@ use_these_perms:
 	if (is_key_possessed(key_ref))
 		kperm |= key->perm >> 24;
 
-	kperm = kperm & perm & KEY_NEED_ALL;
-
-	if (kperm != perm)
+	if ((kperm & mask) != mask)
 		return -EACCES;
 
 	/* let LSM be the final arbiter */
-	return security_key_permission(key_ref, cred, perm);
+lsm:
+	return security_key_permission(key_ref, cred, need_perm);
 }
 EXPORT_SYMBOL(key_task_permission);
 
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index 09541de31f2f..7e0232db1707 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -609,7 +609,7 @@ bool lookup_user_key_possessed(const struct key *key,
  * returned key reference.
  */
 key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
-			  key_perm_t perm)
+			  enum key_need_perm need_perm)
 {
 	struct keyring_search_context ctx = {
 		.match_data.cmp		= lookup_user_key_possessed,
@@ -773,35 +773,33 @@ try_again:
 
 	/* unlink does not use the nominated key in any way, so can skip all
 	 * the permission checks as it is only concerned with the keyring */
-	if (lflags & KEY_LOOKUP_FOR_UNLINK) {
-		ret = 0;
-		goto error;
-	}
-
-	if (!(lflags & KEY_LOOKUP_PARTIAL)) {
-		ret = wait_for_key_construction(key, true);
-		switch (ret) {
-		case -ERESTARTSYS:
-			goto invalid_key;
-		default:
-			if (perm)
+	if (need_perm != KEY_NEED_UNLINK) {
+		if (!(lflags & KEY_LOOKUP_PARTIAL)) {
+			ret = wait_for_key_construction(key, true);
+			switch (ret) {
+			case -ERESTARTSYS:
+				goto invalid_key;
+			default:
+				if (need_perm != KEY_AUTHTOKEN_OVERRIDE &&
+				    need_perm != KEY_DEFER_PERM_CHECK)
+					goto invalid_key;
+			case 0:
+				break;
+			}
+		} else if (need_perm != KEY_DEFER_PERM_CHECK) {
+			ret = key_validate(key);
+			if (ret < 0)
 				goto invalid_key;
-		case 0:
-			break;
 		}
-	} else if (perm) {
-		ret = key_validate(key);
-		if (ret < 0)
+
+		ret = -EIO;
+		if (!(lflags & KEY_LOOKUP_PARTIAL) &&
+		    key_read_state(key) == KEY_IS_UNINSTANTIATED)
 			goto invalid_key;
 	}
 
-	ret = -EIO;
-	if (!(lflags & KEY_LOOKUP_PARTIAL) &&
-	    key_read_state(key) == KEY_IS_UNINSTANTIATED)
-		goto invalid_key;
-
 	/* check the permissions */
-	ret = key_task_permission(key_ref, ctx.cred, perm);
+	ret = key_task_permission(key_ref, ctx.cred, need_perm);
 	if (ret < 0)
 		goto invalid_key;