[PATCH 6.18 419/752] Bluetooth: L2CAP: Fix invalid response to L2CAP_ECRED_RECONF_REQ

Sasha Levin
2026-02-28T17:53:59Z

From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

[ Upstream commit 7accb1c4321acb617faf934af59d928b0b047e2b ]

This fixes responding with an invalid result caused by checking the
wrong size of CID which should have been (cmd_len - sizeof(*req)) and
on top of it the wrong result was use L2CAP_CR_LE_INVALID_PARAMS which
is invalid/reserved for reconf when running test like L2CAP/ECFC/BI-03-C:

> ACL Data RX: Handle 64 flags 0x02 dlen 14
LE L2CAP: Enhanced Credit Reconfigure Request (0x19) ident 2 len 6
MTU: 64
MPS: 64
Source CID: 64
< ACL Data TX: Handle 64 flags 0x00 dlen 10
LE L2CAP: Enhanced Credit Reconfigure Respond (0x1a) ident 2 len 2
! Result: Reserved (0x000c)
Result: Reconfiguration failed - one or more Destination CIDs invalid (0x0003)

Fiix L2CAP/ECFC/BI-04-C which expects L2CAP_RECONF_INVALID_MPS (0x0002)
when more than one channel gets its MPS reduced:

> ACL Data RX: Handle 64 flags 0x02 dlen 16
LE L2CAP: Enhanced Credit Reconfigure Request (0x19) ident 2 len 8
MTU: 264
MPS: 99
Source CID: 64
! Source CID: 65
< ACL Data TX: Handle 64 flags 0x00 dlen 10
LE L2CAP: Enhanced Credit Reconfigure Respond (0x1a) ident 2 len 2
! Result: Reconfiguration successful (0x0000)
Result: Reconfiguration failed - reduction in size of MPS not allowed for more than one channel at a time (0x0002)

Fix L2CAP/ECFC/BI-05-C when SCID is invalid (85 unconnected):

> ACL Data RX: Handle 64 flags 0x02 dlen 14
LE L2CAP: Enhanced Credit Reconfigure Request (0x19) ident 2 len 6
MTU: 65
MPS: 64
! Source CID: 85
< ACL Data TX: Handle 64 flags 0x00 dlen 10
LE L2CAP: Enhanced Credit Reconfigure Respond (0x1a) ident 2 len 2
! Result: Reconfiguration successful (0x0000)
Result: Reconfiguration failed - one or more Destination CIDs invalid (0x0003)

Fix L2CAP/ECFC/BI-06-C when MPS < L2CAP_ECRED_MIN_MPS (64):

> ACL Data RX: Handle 64 flags 0x02 dlen 14
LE L2CAP: Enhanced Credit Reconfigure Request (0x19) ident 2 len 6
MTU: 672
! MPS: 63
Source CID: 64
< ACL Data TX: Handle 64 flags 0x00 dlen 10
LE L2CAP: Enhanced Credit Reconfigure Respond (0x1a) ident 2 len 2
! Result: Reconfiguration failed - reduction in size of MPS not allowed for more than one channel at a time (0x0002)
Result: Reconfiguration failed - other unacceptable parameters (0x0004)

Fix L2CAP/ECFC/BI-07-C when MPS reduced for more than one channel:

> ACL Data RX: Handle 64 flags 0x02 dlen 16
LE L2CAP: Enhanced Credit Reconfigure Request (0x19) ident 3 len 8
MTU: 84
! MPS: 71
Source CID: 64
! Source CID: 65
< ACL Data TX: Handle 64 flags 0x00 dlen 10
LE L2CAP: Enhanced Credit Reconfigure Respond (0x1a) ident 2 len 2
! Result: Reconfiguration successful (0x0000)
Result: Reconfiguration failed - reduction in size of MPS not allowed for more than one channel at a time (0x0002)

Link: https://github.com/bluez/bluez/issues/1865
Fixes: 15f02b910562 ("Bluetooth: L2CAP: Add initial code for Enhanced Credit Based Mode")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/bluetooth/l2cap.h | 2 ++
net/bluetooth/l2cap_core.c | 63 +++++++++++++++++++++++++----------
2 files changed, 47 insertions(+), 18 deletions(-)

diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index 00e182a22720a..9820ccc379f1c 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -493,6 +493,8 @@ struct l2cap_ecred_reconf_req {
#define L2CAP_RECONF_SUCCESS 0x0000
#define L2CAP_RECONF_INVALID_MTU 0x0001
#define L2CAP_RECONF_INVALID_MPS 0x0002
+#define L2CAP_RECONF_INVALID_CID 0x0003
+#define L2CAP_RECONF_INVALID_PARAMS 0x0004

struct l2cap_ecred_reconf_rsp {
__le16 result;
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 07b493331fd78..e705b4a171dec 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -5294,14 +5294,14 @@ static inline int l2cap_ecred_reconf_req(struct l2cap_conn *conn,
struct l2cap_ecred_reconf_req *req = (void *) data;
struct l2cap_ecred_reconf_rsp rsp;
u16 mtu, mps, result;
- struct l2cap_chan *chan;
+ struct l2cap_chan *chan[L2CAP_ECRED_MAX_CID] = {};
int i, num_scid;

if (!enable_ecred)
return -EINVAL;

- if (cmd_len < sizeof(*req) || cmd_len - sizeof(*req) % sizeof(u16)) {
- result = L2CAP_CR_LE_INVALID_PARAMS;
+ if (cmd_len < sizeof(*req) || (cmd_len - sizeof(*req)) % sizeof(u16)) {
+ result = L2CAP_RECONF_INVALID_CID;
goto respond;
}

@@ -5311,42 +5311,69 @@ static inline int l2cap_ecred_reconf_req(struct l2cap_conn *conn,
BT_DBG("mtu %u mps %u", mtu, mps);

if (mtu < L2CAP_ECRED_MIN_MTU) {
- result = L2CAP_RECONF_INVALID_MTU;
+ result = L2CAP_RECONF_INVALID_PARAMS;
goto respond;
}

if (mps < L2CAP_ECRED_MIN_MPS) {
- result = L2CAP_RECONF_INVALID_MPS;
+ result = L2CAP_RECONF_INVALID_PARAMS;
goto respond;
}

cmd_len -= sizeof(*req);
num_scid = cmd_len / sizeof(u16);
+
+ if (num_scid > L2CAP_ECRED_MAX_CID) {
+ result = L2CAP_RECONF_INVALID_PARAMS;
+ goto respond;
+ }
+
result = L2CAP_RECONF_SUCCESS;

+ /* Check if each SCID, MTU and MPS are valid */
for (i = 0; i < num_scid; i++) {
u16 scid;

scid = __le16_to_cpu(req->scid[i]);
- if (!scid)
- return -EPROTO;
+ if (!scid) {
+ result = L2CAP_RECONF_INVALID_CID;
+ goto respond;
+ }

- chan = __l2cap_get_chan_by_dcid(conn, scid);
- if (!chan)
- continue;
+ chan[i] = __l2cap_get_chan_by_dcid(conn, scid);
+ if (!chan[i]) {
+ result = L2CAP_RECONF_INVALID_CID;
+ goto respond;
+ }

- /* If the MTU value is decreased for any of the included
- * channels, then the receiver shall disconnect all
- * included channels.
+ /* The MTU field shall be greater than or equal to the greatest
+ * current MTU size of these channels.
*/
- if (chan->omtu > mtu) {
- BT_ERR("chan %p decreased MTU %u -> %u", chan,
- chan->omtu, mtu);
+ if (chan[i]->omtu > mtu) {
+ BT_ERR("chan %p decreased MTU %u -> %u", chan[i],
+ chan[i]->omtu, mtu);
result = L2CAP_RECONF_INVALID_MTU;
+ goto respond;
}

- chan->omtu = mtu;
- chan->remote_mps = mps;
+ /* If more than one channel is being configured, the MPS field
+ * shall be greater than or equal to the current MPS size of
+ * each of these channels. If only one channel is being
+ * configured, the MPS field may be less than the current MPS
+ * of that channel.
+ */
+ if (chan[i]->remote_mps >= mps && i) {
+ BT_ERR("chan %p decreased MPS %u -> %u", chan[i],
+ chan[i]->remote_mps, mps);
+ result = L2CAP_RECONF_INVALID_MPS;
+ goto respond;
+ }
+ }
+
+ /* Commit the new MTU and MPS values after checking they are valid */
+ for (i = 0; i < num_scid; i++) {
+ chan[i]->omtu = mtu;
+ chan[i]->remote_mps = mps;
}

respond:
--
2.51.0