ksmbd: validate payload size in ipc response

If installing malicious ksmbd-tools, ksmbd.mountd can return invalid ipc
response to ksmbd kernel server. ksmbd should validate payload size of
ipc response from ksmbd.mountd to avoid memory overrun or
slab-out-of-bounds. This patch validate 3 ipc response that has payload.

Reported-by: Chao Ma <machao2019@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

ksmbd_netlink.h

@@ -167,7 +167,8 @@ struct ksmbd_share_config_response {
 	__u16	force_uid;
 	__u16	force_gid;
 	__s8	share_name[KSMBD_REQ_MAX_SHARE_NAME];
-	__u32	reserved[112];		/* Reserved room */
+	__u32	reserved[111];		/* Reserved room */
+	__u32	payload_sz;
 	__u32	veto_list_sz;
 	__s8	____payload[];
 };

mgmt/share_config.c

@@ -158,7 +158,12 @@ static struct ksmbd_share_config *share_config_request(struct unicode_map *um,
 	share->name = kstrdup(name, GFP_KERNEL);
 
 	if (!test_share_config_flag(share, KSMBD_SHARE_FLAG_PIPE)) {
-		share->path = kstrdup(ksmbd_share_config_path(resp),
+		int path_len = PATH_MAX;
+
+		if (resp->payload_sz)
+			path_len = resp->payload_sz - resp->veto_list_sz;
+
+		share->path = kstrndup(ksmbd_share_config_path(resp), path_len,
 				      GFP_KERNEL);
 		if (share->path)
 			share->path_sz = strlen(share->path);

transport_ipc.c

@@ -65,6 +65,7 @@ struct ipc_msg_table_entry {
 	struct hlist_node	ipc_table_hlist;
 
 	void			*response;
+	unsigned int		msg_sz;
 };
 
 static struct delayed_work ipc_timer_work;
@@ -277,6 +278,7 @@ static int handle_response(int type, void *payload, size_t sz)
 		}
 
 		memcpy(entry->response, payload, sz);
+		entry->msg_sz = sz;
 		wake_up_interruptible(&entry->wait);
 		ret = 0;
 		break;
@@ -455,6 +457,34 @@ static int ipc_msg_send(struct ksmbd_ipc_msg *msg)
 	return ret;
 }
 
+static int ipc_validate_msg(struct ipc_msg_table_entry *entry)
+{
+	unsigned int msg_sz = entry->msg_sz;
+
+	if (entry->type == KSMBD_EVENT_RPC_REQUEST) {
+		struct ksmbd_rpc_command *resp = entry->response;
+
+		msg_sz = sizeof(struct ksmbd_rpc_command) + resp->payload_sz;
+	} else if (entry->type == KSMBD_EVENT_SPNEGO_AUTHEN_REQUEST) {
+		struct ksmbd_spnego_authen_response *resp = entry->response;
+
+		msg_sz = sizeof(struct ksmbd_spnego_authen_response) +
+				resp->session_key_len + resp->spnego_blob_len;
+	} else if (entry->type == KSMBD_EVENT_SHARE_CONFIG_REQUEST) {
+		struct ksmbd_share_config_response *resp = entry->response;
+
+		if (resp->payload_sz) {
+			if (resp->payload_sz < resp->veto_list_sz)
+				return -EINVAL;
+
+			msg_sz = sizeof(struct ksmbd_share_config_response) +
+					resp->payload_sz;
+		}
+	}
+
+	return entry->msg_sz != msg_sz ? -EINVAL : 0;
+}
+
 static void *ipc_msg_send_request(struct ksmbd_ipc_msg *msg, unsigned int handle)
 {
 	struct ipc_msg_table_entry entry;
@@ -479,6 +509,13 @@ static void *ipc_msg_send_request(struct ksmbd_ipc_msg *msg, unsigned int handle
 	ret = wait_event_interruptible_timeout(entry.wait,
 					       entry.response != NULL,
 					       IPC_WAIT_TIMEOUT);
+	if (entry.response) {
+		ret = ipc_validate_msg(&entry);
+		if (ret) {
+			kvfree(entry.response);
+			entry.response = NULL;
+		}
+	}
 out:
 	down_write(&ipc_msg_table_lock);
 	hash_del(&entry.ipc_table_hlist);