security: Fix hook iteration and default value for inode_copy_up_xattr

inode_copy_up_xattr returns 0 to indicate the acceptance of the xattr
and 1 to reject it. If the LSM does not know about the xattr, it's
expected to return -EOPNOTSUPP, which is the correct default value for
this hook. BPF LSM, currently, uses 0 as the default value and thereby
falsely allows all overlay fs xattributes to be copied up.

The iteration logic is also updated from the "bail-on-fail"
call_int_hook to continue on the non-decisive -EOPNOTSUPP and bail out
on other values.

Fixes: 98e828a ("security: Refactor declaration of LSM hooks")
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: James Morris <jmorris@namei.org>

include/linux/lsm_hook_defs.h

@@ -150,7 +150,7 @@ LSM_HOOK(int, 0, inode_listsecurity, struct inode *inode, char *buffer,
 	 size_t buffer_size)
 LSM_HOOK(void, LSM_RET_VOID, inode_getsecid, struct inode *inode, u32 *secid)
 LSM_HOOK(int, 0, inode_copy_up, struct dentry *src, struct cred **new)
-LSM_HOOK(int, 0, inode_copy_up_xattr, const char *name)
+LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, const char *name)
 LSM_HOOK(int, 0, kernfs_init_security, struct kernfs_node *kn_dir,
 	 struct kernfs_node *kn)
 LSM_HOOK(int, 0, file_permission, struct file *file, int mask)

security/security.c

@@ -1414,7 +1414,22 @@ EXPORT_SYMBOL(security_inode_copy_up);
 
 int security_inode_copy_up_xattr(const char *name)
 {
-	return call_int_hook(inode_copy_up_xattr, -EOPNOTSUPP, name);
+	struct security_hook_list *hp;
+	int rc;
+
+	/*
+	 * The implementation can return 0 (accept the xattr), 1 (discard the
+	 * xattr), -EOPNOTSUPP if it does not know anything about the xattr or
+	 * any other error code incase of an error.
+	 */
+	hlist_for_each_entry(hp,
+		&security_hook_heads.inode_copy_up_xattr, list) {
+		rc = hp->hook.inode_copy_up_xattr(name);
+		if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
+			return rc;
+	}
+
+	return LSM_RET_DEFAULT(inode_copy_up_xattr);
 }
 EXPORT_SYMBOL(security_inode_copy_up_xattr);