Bluetooth: l2cap: fix MPS check in l2cap_ecred_reconf_req

The L2CAP specification states that if more than one channel is being reconfigured, the MPS shall not be decreased. The current check has two issues:

1) The comparison uses >= (greater-than-or-equal), which incorrectly rejects reconfiguration requests where the MPS stays the same. Since the spec says MPS "shall be greater than or equal to the current MPS", only a strict decrease (remote_mps > mps) should be rejected. Keeping the same MPS is valid.

2) The multi-channel guard uses && i (loop index) to approximate "more than one channel", but this incorrectly allows MPS decrease for the first channel (i==0) even when multiple channels are being reconfigured. Replace with && num_scid > 1 which correctly checks whether the request covers more than one channel.

---
 net/bluetooth/l2cap_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 95c65fece39b..29d793f3a2eb 100644
@@ -5428,7 +5428,7 @@ static inline int l2cap_ecred_reconf_req(struct l2cap_conn *conn,
 		 * configured, the MPS field may be less than the current MPS
 		 * of that channel.
 		 */
-		if (chan[i]->remote_mps >= mps && i) {
+		if (chan[i]->remote_mps > mps && num_scid > 1) {
 			BT_ERR("chan %p decreased MPS %u -> %u", chan[i],
 			       chan[i]->remote_mps, mps);
 			result = L2CAP_RECONF_INVALID_MPS;

2.39.3 (Apple Git-145)

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Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list. This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=1081515

---Test result---

Test Summary:

CheckPatch                    PASS      0.57 seconds
GitLint                       PASS      0.23 seconds
SubjectPrefix                 PASS      0.08 seconds
BuildKernel                   PASS      26.28 seconds
CheckAllWarning               PASS      28.48 seconds
CheckSparse                   PASS      30.18 seconds
BuildKernel32                 PASS      25.12 seconds
TestRunnerSetup               PASS      563.75 seconds
TestRunner_l2cap-tester       FAIL      28.18 seconds
TestRunner_iso-tester         PASS      41.64 seconds
TestRunner_bnep-tester        PASS      6.30 seconds
TestRunner_mgmt-tester        FAIL      115.32 seconds
TestRunner_rfcomm-tester      PASS      9.93 seconds
TestRunner_sco-tester         FAIL      14.26 seconds
TestRunner_ioctl-tester       PASS      10.20 seconds
TestRunner_mesh-tester        FAIL      12.16 seconds
TestRunner_smp-tester         PASS      8.57 seconds
TestRunner_userchan-tester    PASS      6.80 seconds
TestRunner_6lowpan-tester     FAIL      8.46 seconds
IncrementalBuild              PASS      24.79 seconds

Details
##############################
Test: TestRunner_l2cap-tester - FAIL
Desc: Run l2cap-tester with test-runner Output:
Total: 96, Passed: 94 (97.9%), Failed: 2, Not Run: 0

Failed Test Cases

L2CAP BR/EDR Client - Set PHY 3M                     Failed       0.112 seconds
L2CAP BR/EDR Server - Set PHY 3M                     Failed       0.120 seconds

##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner Output:
Total: 494, Passed: 489 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
Read Exp Feature - Success Failed 0.114 seconds
##############################
Test: TestRunner_sco-tester - FAIL
Desc: Run sco-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
7.0.0-rc2-g7259c040a595 #1 Not tainted
------------------------------------------------------
kworker/u5:2/117 is trying to acquire lock:
ffff888001abe240 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}, at: sco_connect_cfm+0x358/0x8d0

but task is already holding lock:
ffff888002094c20 (&conn->lock){+.+.}-{3:3}, at: sco_connect_cfm+0x22d/0x8d0

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&conn->lock){+.+.}-{3:3}:

       lock_acquire+0xf7/0x2c0
       _raw_spin_lock+0x2a/0x40
       sco_sock_connect+0x4d7/0x1280
       __sys_connect+0x1a3/0x260
       __x64_sys_connect+0x6e/0xb0
       do_syscall_64+0xa0/0x570
       entry_SYSCALL_64_after_hwframe+0x74/0x7c

-> #0 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}:

       check_prev_add+0xe9/0xc70
       __lock_acquire+0x1457/0x1df0
       lock_acquire+0xf7/0x2c0
       lock_sock_nested+0x36/0xd0
       sco_connect_cfm+0x358/0x8d0
       hci_sync_conn_complete_evt+0x3d3/0x8e0
       hci_event_packet+0x74f/0xb10
       hci_rx_work+0x398/0xd00
       process_scheduled_works+0xb16/0x1ac0
       worker_thread+0x4ff/0xba0
       kthread+0x368/0x490
       ret_from_fork+0x498/0x7e0
       ret_from_fork_asm+0x19/0x30

other info that might help us debug this:

...

BUG: sleeping function called from invalid context at net/core/sock.c:3782

in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 117, name: kworker/u5:2
preempt_count: 1, expected: 0
RCU nest depth: 0, expected: 0
INFO: lockdep is turned off.

CPU: 0 UID: 0 PID: 117 Comm: kworker/u5:2 Not tainted 7.0.0-rc2-g7259c040a595 #1 PREEMPT(lazy) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Workqueue: hci0 hci_rx_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x49/0x60
 __might_resched+0x2ea/0x500
 lock_sock_nested+0x47/0xd0
 ? sco_connect_cfm+0x358/0x8d0
 sco_connect_cfm+0x358/0x8d0
 ? hci_debugfs_create_conn+0x190/0x210
 ? __pfx_sco_connect_cfm+0x10/0x10
 hci_sync_conn_complete_evt+0x3d3/0x8e0
 hci_event_packet+0x74f/0xb10
 ? __pfx_hci_sync_conn_complete_evt+0x10/0x10
 ? __pfx_hci_event_packet+0x10/0x10
 ? mark_held_locks+0x49/0x80
 ? lockdep_hardirqs_on_prepare+0xd4/0x180
 ? _raw_spin_unlock_irqrestore+0x2c/0x50
 hci_rx_work+0x398/0xd00
 process_scheduled_works+0xb16/0x1ac0
 ? __pfx_process_scheduled_works+0x10/0x10
 ? lock_acquire+0xf7/0x2c0
 ? lock_is_held_type+0x9b/0x110
 ? __pfx_hci_rx_work+0x10/0x10
 worker_thread+0x4ff/0xba0
 ? _raw_spin_unlock_irqrestore+0x2c/0x50
 ? __pfx_worker_thread+0x10/0x10
 kthread+0x368/0x490
 ? _raw_spin_unlock_irq+0x23/0x40
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x498/0x7e0
 ? __pfx_ret_from_fork+0x10/0x10
 ? __switch_to+0x9e4/0xe50
 ? __switch_to_asm+0x32/0x60

...
Total: 30, Passed: 30 (100.0%), Failed: 0, Not Run: 0
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases

Mesh - Send cancel - 1                               Timed out    2.654 seconds
Mesh - Send cancel - 2                               Timed out    1.994 seconds

##############################
Test: TestRunner_6lowpan-tester - FAIL
Desc: Run 6lowpan-tester with test-runner
Output:
WARNING: possible circular locking dependency detected 7.0.0-rc2-g7259c040a595 #1 Not tainted
------------------------------------------------------
kworker/0:1/11 is trying to acquire lock:
ffff888002767140 ((wq_completion)hci0#2){+.+.}-{0:0}, at: touch_wq_lockdep_map+0x75/0x180

but task is already holding lock:
ffffffffb644d720 (rtnl_mutex){+.+.}-{4:4}, at: lowpan_unregister_netdev+0xd/0x30

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #4 (rtnl_mutex){+.+.}-{4:4}:

       lock_acquire+0xf7/0x2c0
       __mutex_lock+0x16b/0x1fc0
       lowpan_register_netdev+0x11/0x30
       chan_ready_cb+0x836/0xd00
       l2cap_recv_frame+0x6465/0x8910
       l2cap_recv_acldata+0x790/0xdf0
       hci_rx_work+0x500/0xd00
       process_scheduled_works+0xb16/0x1ac0
       worker_thread+0x4ff/0xba0
       kthread+0x368/0x490
       ret_from_fork+0x498/0x7e0
       ret_from_fork_asm+0x19/0x30

-> #3 (&chan->lock#3/1){+.+.}-{4:4}:

       lock_acquire+0xf7/0x2c0
       __mutex_lock+0x16b/0x1fc0
       l2cap_chan_connect+0x74e/0x1980
       lowpan_control_write+0x523/0x660
       full_proxy_write+0x10b/0x190
       vfs_write+0x1c0/0xf60
       ksys_write+0xf1/0x1d0
       do_syscall_64+0xa0/0x570
       entry_SYSCALL_64_after_hwframe+0x74/0x7c

-> #2 (&conn->lock){+.+.}-{4:4}:
...
Total: 8, Passed: 8 (100.0%), Failed: 0, Not Run: 0

https://github.com/bluez/bluetooth-next/pull/87

---
Regards,
Linux Bluetooth