ksmbd: fix translation in sid_to_id()

The sid_to_id() functions is relevant when changing ownership of
filesystem objects based on acl information. In this case we need to
first translate the relevant s*ids into k*ids in ksmbd's user namespace
and account for any idmapped mounts. Requesting a change in ownership
requires the inverse translation to be applied when we would report
ownership to userspace. So k*id_from_mnt() must be used here.

Cc: Steve French <stfrench@microsoft.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: Hyunchul Lee <hyc.lee@gmail.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/smbacl.c

@@ -275,8 +275,15 @@ static int sid_to_id(struct user_namespace *user_ns,
 
 		id = le32_to_cpu(psid->sub_auth[psid->num_subauth - 1]);
 		if (id >= 0) {
-			uid = make_kuid(user_ns, id);
-			if (uid_valid(uid) && kuid_has_mapping(user_ns, uid)) {
+			/*
+			 * Translate raw sid into kuid in the server's user
+			 * namespace.
+			 */
+			uid = make_kuid(&init_user_ns, id);
+
+			/* If this is an idmapped mount, apply the idmapping. */
+			uid = kuid_from_mnt(user_ns, uid);
+			if (uid_valid(uid)) {
 				fattr->cf_uid = uid;
 				rc = 0;
 			}
@@ -287,8 +294,15 @@ static int sid_to_id(struct user_namespace *user_ns,
 
 		id = le32_to_cpu(psid->sub_auth[psid->num_subauth - 1]);
 		if (id >= 0) {
-			gid = make_kgid(user_ns, id);
-			if (gid_valid(gid) && kgid_has_mapping(user_ns, gid)) {
+			/*
+			 * Translate raw sid into kgid in the server's user
+			 * namespace.
+			 */
+			gid = make_kgid(&init_user_ns, id);
+
+			/* If this is an idmapped mount, apply the idmapping. */
+			gid = kgid_from_mnt(user_ns, gid);
+			if (gid_valid(gid)) {
 				fattr->cf_gid = gid;
 				rc = 0;
 			}