Fix MTU value used on MTU exchange response
ATT_MTU_RESP shall send the original MTU value prior to the exchange. If
client sends an invalid value, the server shall use the ATT_DEFAULT_LE_MTU
value. This operation is not supported in BR/EDR, so if any client sends
this request it will be ignored by server and it will reply with
"Request not supported".
For BR/EDR, the MTU is limited to ATT_MAX_MTU (currently 256). This
avoids allocating a big buffer when most ATT PDUs are small.
Note: the kernel currently limits the minimum MTU to 48, regardless of
transport type. This limit is valid only for BR/EDR, for LE the minimum
is 23. This bug will be fixed, but it does not affect the outgoing MTU
for new created LE sockets, which are correctly set to 23.
diff --git a/src/attrib-server.c b/src/attrib-server.c
index 61db851..8464d2a 100644
--- a/src/attrib-server.c
+++ b/src/attrib-server.c
@@ -59,6 +59,7 @@
GSList *indicate;
GAttrib *attrib;
guint mtu;
+ gboolean le;
guint id;
gboolean encrypted;
};
@@ -759,9 +760,18 @@
static uint16_t mtu_exchange(struct gatt_channel *channel, uint16_t mtu,
uint8_t *pdu, int len)
{
- channel->mtu = MIN(mtu, channel->mtu);
+ guint old_mtu = channel->mtu;
- return enc_mtu_resp(channel->mtu, pdu, len);
+ if (mtu < ATT_DEFAULT_LE_MTU)
+ channel->mtu = ATT_DEFAULT_LE_MTU;
+ else
+ channel->mtu = MIN(mtu, channel->mtu);
+
+ bt_io_set(le_io, BT_IO_L2CAP, NULL,
+ BT_IO_OPT_OMTU, channel->mtu,
+ BT_IO_OPT_INVALID);
+
+ return enc_mtu_resp(old_mtu, pdu, len);
}
static void channel_disconnect(void *user_data)
@@ -831,6 +841,11 @@
length = read_blob(channel, start, offset, opdu, channel->mtu);
break;
case ATT_OP_MTU_REQ:
+ if (!channel->le) {
+ status = ATT_ECODE_REQ_NOT_SUPP;
+ goto done;
+ }
+
length = dec_mtu_req(ipdu, len, &mtu);
if (length == 0) {
status = ATT_ECODE_INVALID_PDU;
@@ -913,6 +928,7 @@
BT_IO_OPT_SOURCE_BDADDR, &channel->src,
BT_IO_OPT_DEST_BDADDR, &channel->dst,
BT_IO_OPT_CID, &cid,
+ BT_IO_OPT_OMTU, &channel->mtu,
BT_IO_OPT_INVALID);
if (gerr) {
error("bt_io_get: %s", gerr->message);
@@ -922,10 +938,13 @@
return;
}
+ if (channel->mtu > ATT_MAX_MTU)
+ channel->mtu = ATT_MAX_MTU;
+
if (cid != GATT_CID)
- channel->mtu = ATT_DEFAULT_L2CAP_MTU;
+ channel->le = FALSE;
else
- channel->mtu = ATT_DEFAULT_LE_MTU;
+ channel->le = TRUE;
channel->attrib = g_attrib_new(io);
g_io_channel_unref(io);
