[PATCH v2] Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

[PATCH v2] Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

[Hyunwoo Kim]

l2cap_config_req() processes CONFIG_REQ for channels in BT_CONNECTED
state to support L2CAP reconfiguration (e.g. MTU changes). However,
since both CONF_INPUT_DONE and CONF_OUTPUT_DONE are already set from
the initial configuration, the reconfiguration path falls through to
l2cap_ertm_init(), which re-initializes tx_q, srej_q, srej_list, and
retrans_list without freeing the previous allocations and sets
chan->sdu to NULL without freeing the existing skb. This leaks all
previously allocated ERTM resources.

Additionally, l2cap_parse_conf_req() does not validate the minimum
value of remote_mps derived from the RFC max_pdu_size option. A zero
value propagates to l2cap_segment_sdu() where pdu_len becomes zero,
causing the while loop to never terminate since len is never
decremented, exhausting all available memory.

Fix the double-init by skipping l2cap_ertm_init() and
l2cap_chan_ready() when the channel is already in BT_CONNECTED state,
while still allowing the reconfiguration parameters to be updated
through l2cap_parse_conf_req(). Also add a pdu_len zero check in
l2cap_segment_sdu() as a safeguard.

Fixes: 96298f640104 ("Bluetooth: L2CAP: handle l2cap config request during open state")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
Changes in v2:
- Keep BT_CONNECTED in allowed states for l2cap_config_req()
- Skip l2cap_ertm_init() and l2cap_chan_ready() when already connected
- v1: https://lore.kernel.org/all/abwTCkavRurEcEGO@v4bel/
---
 net/bluetooth/l2cap_core.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 5deb6c4f1e41..b80667c263ef 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -2377,6 +2377,9 @@ static int l2cap_segment_sdu(struct l2cap_chan *chan,
 	/* Remote device may have requested smaller PDUs */
 	pdu_len = min_t(size_t, pdu_len, chan->remote_mps);
 
+	if (!pdu_len)
+		return -EINVAL;
+
 	if (len <= pdu_len) {
 		sar = L2CAP_SAR_UNSEGMENTED;
 		sdu_len = 0;
@@ -4312,14 +4315,16 @@ static inline int l2cap_config_req(struct l2cap_conn *conn,
 	if (test_bit(CONF_INPUT_DONE, &chan->conf_state)) {
 		set_default_fcs(chan);
 
-		if (chan->mode == L2CAP_MODE_ERTM ||
-		    chan->mode == L2CAP_MODE_STREAMING)
-			err = l2cap_ertm_init(chan);
+		if (chan->state != BT_CONNECTED) {
+			if (chan->mode == L2CAP_MODE_ERTM ||
+			    chan->mode == L2CAP_MODE_STREAMING)
+				err = l2cap_ertm_init(chan);
 
-		if (err < 0)
-			l2cap_send_disconn_req(chan, -err);
-		else
-			l2cap_chan_ready(chan);
+			if (err < 0)
+				l2cap_send_disconn_req(chan, -err);
+			else
+				l2cap_chan_ready(chan);
+		}
 
 		goto unlock;
 	}
-- 
2.43.0

RE: [v2] Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

[bluez.test.bot]

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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=1069857

---Test result---

Test Summary:
CheckPatch                    PENDING   0.39 seconds
GitLint                       PENDING   0.30 seconds
SubjectPrefix                 PASS      0.09 seconds
BuildKernel                   PASS      26.91 seconds
CheckAllWarning               PASS      29.45 seconds
CheckSparse                   PASS      28.54 seconds
BuildKernel32                 PASS      26.27 seconds
TestRunnerSetup               PASS      584.59 seconds
TestRunner_l2cap-tester       FAIL      29.51 seconds
TestRunner_iso-tester         FAIL      35.89 seconds
TestRunner_bnep-tester        PASS      6.66 seconds
TestRunner_mgmt-tester        FAIL      118.03 seconds
TestRunner_rfcomm-tester      PASS      9.67 seconds
TestRunner_sco-tester         FAIL      14.74 seconds
TestRunner_ioctl-tester       PASS      10.65 seconds
TestRunner_mesh-tester        FAIL      12.67 seconds
TestRunner_smp-tester         PASS      9.00 seconds
TestRunner_userchan-tester    PASS      6.85 seconds
IncrementalBuild              PENDING   0.58 seconds

Details
##############################
Test: CheckPatch - PENDING
Desc: Run checkpatch.pl script
Output:

##############################
Test: GitLint - PENDING
Desc: Run gitlint
Output:

##############################
Test: TestRunner_l2cap-tester - FAIL
Desc: Run l2cap-tester with test-runner
Output:
Total: 96, Passed: 95 (99.0%), Failed: 1, Not Run: 0

Failed Test Cases
L2CAP BR/EDR Server - Set PHY 2M                     Failed       0.125 seconds
##############################
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       0.117 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    2.608 seconds
Mesh - Send cancel - 2                               Timed out    1.995 seconds
##############################
Test: IncrementalBuild - PENDING
Desc: Incremental build with the patches in the series
Output:



---
Regards,
Linux Bluetooth

Re: [PATCH v2] Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

[patchwork-bot+bluetooth]

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Fri, 20 Mar 2026 20:23:10 +0900 you wrote:
> l2cap_config_req() processes CONFIG_REQ for channels in BT_CONNECTED
> state to support L2CAP reconfiguration (e.g. MTU changes). However,
> since both CONF_INPUT_DONE and CONF_OUTPUT_DONE are already set from
> the initial configuration, the reconfiguration path falls through to
> l2cap_ertm_init(), which re-initializes tx_q, srej_q, srej_list, and
> retrans_list without freeing the previous allocations and sets
> chan->sdu to NULL without freeing the existing skb. This leaks all
> previously allocated ERTM resources.
> 
> [...]

Here is the summary with links:
  - [v2] Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop
    https://git.kernel.org/bluetooth/bluetooth-next/c/acf374fce194

You are awesome, thank you!
-- 
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