* [PATCH] Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop
@ 2026-03-19 15:14 Hyunwoo Kim
2026-03-19 16:36 ` bluez.test.bot
2026-04-09 20:02 ` bluez.test.bot
0 siblings, 2 replies; 3+ messages in thread
From: Hyunwoo Kim @ 2026-03-19 15:14 UTC (permalink / raw)
To: marcel, johan.hedberg, luiz.dentz; +Cc: linux-bluetooth, imv4bel
rfcomm_apply_pn() accepts the MTU value from a remote PN (Parameter
Negotiation) frame without checking for zero. When the remote peer
sends an MTU of zero, d->mtu is set to 0. This causes the sendmsg
path to enter an infinite loop when fragmenting data, as each fragment
has size == min_t(size_t, len, 0) == 0, so the remaining length never
decreases. The infinite allocation of zero-length skbs exhausts all
system memory.
Fix by clamping d->mtu to RFCOMM_DEFAULT_MTU when the negotiated
value is zero, consistent with the initial value assigned in
rfcomm_dlc_alloc().
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
net/bluetooth/rfcomm/core.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index 611a9a94151e..f9b428b1f1c8 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -1423,6 +1423,10 @@ static int rfcomm_apply_pn(struct rfcomm_dlc *d, int cr, struct rfcomm_pn *pn)
d->mtu = __le16_to_cpu(pn->mtu);
+ /* MTU 0 causes an infinite loop when fragmenting in sendmsg */
+ if (!d->mtu)
+ d->mtu = RFCOMM_DEFAULT_MTU;
+
if (cr && d->mtu > s->mtu)
d->mtu = s->mtu;
--
2.43.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* RE: Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop
2026-03-19 15:14 [PATCH] Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop Hyunwoo Kim
@ 2026-03-19 16:36 ` bluez.test.bot
2026-04-09 20:02 ` bluez.test.bot
1 sibling, 0 replies; 3+ messages in thread
From: bluez.test.bot @ 2026-03-19 16:36 UTC (permalink / raw)
To: linux-bluetooth, imv4bel
[-- Attachment #1: Type: text/plain, Size: 2833 bytes --]
This is automated email and please do not reply to this email!
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=1069345
---Test result---
Test Summary:
CheckPatch PENDING 0.48 seconds
GitLint PENDING 0.33 seconds
SubjectPrefix PASS 0.09 seconds
BuildKernel PASS 26.83 seconds
CheckAllWarning PASS 29.62 seconds
CheckSparse PASS 28.26 seconds
BuildKernel32 PASS 26.29 seconds
TestRunnerSetup PASS 577.55 seconds
TestRunner_l2cap-tester PASS 28.22 seconds
TestRunner_iso-tester FAIL 31.50 seconds
TestRunner_bnep-tester PASS 6.50 seconds
TestRunner_mgmt-tester FAIL 116.17 seconds
TestRunner_rfcomm-tester PASS 9.57 seconds
TestRunner_sco-tester FAIL 14.52 seconds
TestRunner_ioctl-tester PASS 10.52 seconds
TestRunner_mesh-tester FAIL 12.56 seconds
TestRunner_smp-tester PASS 8.64 seconds
TestRunner_userchan-tester PASS 6.93 seconds
IncrementalBuild PENDING 0.95 seconds
Details
##############################
Test: CheckPatch - PENDING
Desc: Run checkpatch.pl script
Output:
##############################
Test: GitLint - PENDING
Desc: Run gitlint
Output:
##############################
Test: TestRunner_iso-tester - FAIL
Desc: Run iso-tester with test-runner
Output:
BUG: KASAN: slab-use-after-free in le_read_features_complete+0x7e/0x2b0
Total: 141, Passed: 141 (100.0%), Failed: 0, Not Run: 0
##############################
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 0.109 seconds
##############################
Test: TestRunner_sco-tester - FAIL
Desc: Run sco-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
BUG: sleeping function called from invalid context at net/core/sock.c:3782
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 2.614 seconds
Mesh - Send cancel - 2 Timed out 1.994 seconds
##############################
Test: IncrementalBuild - PENDING
Desc: Incremental build with the patches in the series
Output:
---
Regards,
Linux Bluetooth
^ permalink raw reply [flat|nested] 3+ messages in thread
* RE: Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop
2026-03-19 15:14 [PATCH] Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop Hyunwoo Kim
2026-03-19 16:36 ` bluez.test.bot
@ 2026-04-09 20:02 ` bluez.test.bot
1 sibling, 0 replies; 3+ messages in thread
From: bluez.test.bot @ 2026-04-09 20:02 UTC (permalink / raw)
To: linux-bluetooth, imv4bel
[-- Attachment #1: Type: text/plain, Size: 6877 bytes --]
This is automated email and please do not reply to this email!
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=1069345
---Test result---
Test Summary:
CheckPatch PENDING 0.55 seconds
GitLint PENDING 0.42 seconds
SubjectPrefix PASS 0.06 seconds
BuildKernel PASS 26.13 seconds
CheckAllWarning PASS 28.72 seconds
CheckSparse PASS 27.52 seconds
BuildKernel32 PASS 25.16 seconds
TestRunnerSetup PASS 564.21 seconds
TestRunner_l2cap-tester PASS 27.56 seconds
TestRunner_iso-tester PASS 43.39 seconds
TestRunner_bnep-tester PASS 11.38 seconds
TestRunner_mgmt-tester FAIL 115.13 seconds
TestRunner_rfcomm-tester PASS 9.50 seconds
TestRunner_sco-tester FAIL 14.54 seconds
TestRunner_ioctl-tester PASS 10.30 seconds
TestRunner_mesh-tester FAIL 11.65 seconds
TestRunner_smp-tester PASS 8.74 seconds
TestRunner_userchan-tester PASS 6.81 seconds
TestRunner_6lowpan-tester FAIL 8.82 seconds
IncrementalBuild PENDING 0.43 seconds
Details
##############################
Test: CheckPatch - PENDING
Desc: Run checkpatch.pl script
Output:
##############################
Test: GitLint - PENDING
Desc: Run gitlint
Output:
##############################
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 0.107 seconds
##############################
Test: TestRunner_sco-tester - FAIL
Desc: Run sco-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
7.0.0-rc2-g79a719fe1e1e #1 Not tainted
------------------------------------------------------
kworker/u5:2/117 is trying to acquire lock:
ffff888002415240 (sk_lock-AF_BLUETOOTH-BTPROTO_SCO){+.+.}-{0:0}, at: sco_connect_cfm+0x358/0x8d0
but task is already holding lock:
ffff8880025fe220 (&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-g79a719fe1e1e #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 1.820 seconds
Mesh - Send cancel - 2 Timed out 1.996 seconds
##############################
Test: TestRunner_6lowpan-tester - FAIL
Desc: Run 6lowpan-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
7.0.0-rc2-g79a719fe1e1e #1 Not tainted
------------------------------------------------------
kworker/0:0/9 is trying to acquire lock:
ffff888002760940 ((wq_completion)hci0#2){+.+.}-{0:0}, at: touch_wq_lockdep_map+0x75/0x180
but task is already holding lock:
ffffffffb284d720 (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+0x6a06/0x8920
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
##############################
Test: IncrementalBuild - PENDING
Desc: Incremental build with the patches in the series
Output:
https://github.com/bluez/bluetooth-next/pull/25/checks
---
Regards,
Linux Bluetooth
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-03-19 15:14 [PATCH] Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop Hyunwoo Kim
2026-03-19 16:36 ` bluez.test.bot
2026-04-09 20:02 ` bluez.test.bot
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