Commit 98bcd08b authored by Marcel Holtmann's avatar Marcel Holtmann Committed by David S. Miller
Browse files

[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: default avatarMarcel Holtmann <marcel@holtmann.org>
parent 2266d888

net/bluetooth/rfcomm/core.c

+17 −2
Original line number Diff line number Diff line
@@ -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;
@@ -812,6 +813,9 @@ static int rfcomm_send_pn(struct rfcomm_session *s, int cr, struct rfcomm_dlc *d 
		pn->credits   = 0;

	}



	if (cr && channel_mtu >= 0)

		pn->mtu = htobs(channel_mtu);

	else

		pn->mtu = htobs(d->mtu);



	*ptr = __fcs(buf); ptr++;
@@ -1243,7 +1247,10 @@ static int rfcomm_apply_pn(struct rfcomm_dlc *d, int cr, struct rfcomm_pn *pn) 


	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 @@ static inline void rfcomm_accept_connection(struct rfcomm_session *s) 
	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_exit(rfcomm_exit); 
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");

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