diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c
index 3adab8e10a21..90c5e3edbf46 100644
--- a/fs/smb/server/smbacl.c
+++ b/fs/smb/server/smbacl.c
@@ -270,6 +270,11 @@ static int sid_to_id(struct user_namespace *user_ns,
 		return -EIO;
 	}
 
+	if (psid->num_subauth == 0) {
+		pr_err("%s: zero subauthorities!\n", __func__);
+		return -EIO;
+	}
+
 	if (sidtype == SIDOWNER) {
 		kuid_t uid;
 		uid_t id;