[Bluetooth] Correct RFCOMM channel MTU for broken implementations
Some Bluetooth RFCOMM implementations try to negotiate a bigger channel
MTU than we can support for a particular session. The maximum MTU for
a RFCOMM session is limited through the L2CAP layer. So if the other
side proposes a channel MTU that is bigger than the underlying L2CAP
MTU, we should reduce it to the L2CAP MTU of the session minus five
bytes for the RFCOMM headers.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index 77eab8f..332dd8f 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -55,6 +55,7 @@
#define VERSION "1.8"
static int disable_cfc = 0;
+static int channel_mtu = -1;
static unsigned int l2cap_mtu = RFCOMM_MAX_L2CAP_MTU;
static struct task_struct *rfcomm_thread;
@@ -812,7 +813,10 @@
pn->credits = 0;
}
- pn->mtu = htobs(d->mtu);
+ if (cr && channel_mtu >= 0)
+ pn->mtu = htobs(channel_mtu);
+ else
+ pn->mtu = htobs(d->mtu);
*ptr = __fcs(buf); ptr++;
@@ -1243,7 +1247,10 @@
d->priority = pn->priority;
- d->mtu = s->mtu = btohs(pn->mtu);
+ d->mtu = btohs(pn->mtu);
+
+ if (cr && d->mtu > s->mtu)
+ d->mtu = s->mtu;
return 0;
}
@@ -1770,6 +1777,11 @@
s = rfcomm_session_add(nsock, BT_OPEN);
if (s) {
rfcomm_session_hold(s);
+
+ /* We should adjust MTU on incoming sessions.
+ * L2CAP MTU minus UIH header and FCS. */
+ s->mtu = min(l2cap_pi(nsock->sk)->omtu, l2cap_pi(nsock->sk)->imtu) - 5;
+
rfcomm_schedule(RFCOMM_SCHED_RX);
} else
sock_release(nsock);
@@ -2087,6 +2099,9 @@
module_param(disable_cfc, bool, 0644);
MODULE_PARM_DESC(disable_cfc, "Disable credit based flow control");
+module_param(channel_mtu, int, 0644);
+MODULE_PARM_DESC(channel_mtu, "Default MTU for the RFCOMM channel");
+
module_param(l2cap_mtu, uint, 0644);
MODULE_PARM_DESC(l2cap_mtu, "Default MTU for the L2CAP connection");