[RFC PATCH] Bluetooth: L2CAP: tolerate zero-ident LE credit indications

[RFC PATCH] Bluetooth: L2CAP: tolerate zero-ident LE credit indications

[Kyle Pepper]

A nonconforming ASHA peer sends identifier-zero credit indications
that are discarded, reducing usable transmit credits until audio stalls.

Tolerate only exact-size credit indications for a connected LE CoC.
Preserve the channel reference, lock and credit-overflow checks and do
not send a response with identifier zero. Other zero-ID commands and
BR/EDR signaling remain unchanged.

Core Vol 3 Part A section 4 forbids identifier zero. This is an
interoperability RFC requiring maintainer agreement, not a conformance
fix or a claim of automatic stream recovery.

Assisted-by: OpenCode:gpt-6.1-sol
Signed-off-by: Kyle Pepper <cochcoder@proton.me>
---
Submission review notes (not part of the commit message):
Core specification forbids identifier zero. This is a narrow opcode
interoperability exception, not a conformance fix. N8 captures contain
zero-ID credit indications. Native malformed/overflow/teardown and
lockdep/KASAN coverage and exception policy remain review gates.

 net/bluetooth/l2cap_core.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 49a998804..1a0868437 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -5328,6 +5328,12 @@ static inline int l2cap_le_credits(struct l2cap_conn *conn,
 
 	l2cap_chan_lock(chan);
 
+	/* Tolerate identifier-zero credits only for a live LE CoC. */
+	if (!cmd->ident &&
+	    (!credits || chan->state != BT_CONNECTED ||
+	     chan->mode != L2CAP_MODE_LE_FLOWCTL))
+		goto unlock;
+
 	max_credits = LE_FLOWCTL_MAX_CREDITS - chan->tx_credits;
 	if (credits > max_credits) {
 		BT_ERR("LE credits overflow");
@@ -5923,11 +5929,21 @@ static inline void l2cap_le_sig_channel(struct l2cap_conn *conn,
 
 	BT_DBG("code 0x%2.2x len %d id 0x%2.2x", cmd->code, len, cmd->ident);
 
-	if (len != skb->len || !cmd->ident) {
+	if (len != skb->len) {
 		BT_DBG("corrupted command");
 		goto drop;
 	}
 
+	if (!cmd->ident) {
+		if (cmd->code != L2CAP_LE_CREDITS ||
+		    len != sizeof(struct l2cap_le_credits))
+			goto drop;
+
+		/* Credits have no response or identifier-matched transaction. */
+		l2cap_le_credits(conn, cmd, len, skb->data);
+		goto drop;
+	}
+
 	err = l2cap_le_sig_cmd(conn, cmd, len, skb->data);
 	if (err) {
 		struct l2cap_cmd_rej_unk rej;

base-commit: 964430c038967fd06643e866f68115664e1a1bd1

RE: [RFC] Bluetooth: L2CAP: tolerate zero-ident LE credit indications

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 1073 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/series/1184328/

---Test result---

Test Summary:
CheckPatch                    PASS      0.52 seconds
VerifyFixes                   PASS      0.08 seconds
VerifySignedoff               PASS      0.08 seconds
GitLint                       PASS      0.23 seconds
SubjectPrefix                 PASS      0.07 seconds
BuildKernel                   PASS      21.37 seconds
CheckAllWarning               PASS      25.54 seconds
CheckSparse                   PASS      27.19 seconds
BuildKernel32                 PASS      22.33 seconds
CheckKernelLLVM               PASS      24.27 seconds
TestRunnerSetup               PASS      508.85 seconds
TestRunner_l2cap-tester       PASS      13.31 seconds
IncrementalBuild              PASS      20.81 seconds



https://github.com/bluez/bluetooth-next/pull/907

---
Regards,
Linux Bluetooth

Re: [RFC PATCH] Bluetooth: L2CAP: tolerate zero-ident LE credit indications

[Luiz Augusto von Dentz]

Hi Kyle,

On Mon, Oct 12, 2026 at 11:20 PM Kyle Pepper <cochcoder@proton.me> wrote:
>
> A nonconforming ASHA peer sends identifier-zero credit indications
> that are discarded, reducing usable transmit credits until audio stalls.
>
> Tolerate only exact-size credit indications for a connected LE CoC.
> Preserve the channel reference, lock and credit-overflow checks and do
> not send a response with identifier zero. Other zero-ID commands and
> BR/EDR signaling remain unchanged.
>
> Core Vol 3 Part A section 4 forbids identifier zero. This is an
> interoperability RFC requiring maintainer agreement, not a conformance
> fix or a claim of automatic stream recovery.
>
> Assisted-by: OpenCode:gpt-6.1-sol
> Signed-off-by: Kyle Pepper <cochcoder@proton.me>
> ---
> Submission review notes (not part of the commit message):
> Core specification forbids identifier zero. This is a narrow opcode
> interoperability exception, not a conformance fix. N8 captures contain
> zero-ID credit indications. Native malformed/overflow/teardown and
> lockdep/KASAN coverage and exception policy remain review gates.
>
>  net/bluetooth/l2cap_core.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 49a998804..1a0868437 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -5328,6 +5328,12 @@ static inline int l2cap_le_credits(struct l2cap_conn *conn,
>
>         l2cap_chan_lock(chan);
>
> +       /* Tolerate identifier-zero credits only for a live LE CoC. */
> +       if (!cmd->ident &&
> +           (!credits || chan->state != BT_CONNECTED ||
> +            chan->mode != L2CAP_MODE_LE_FLOWCTL))
> +               goto unlock;
> +
>         max_credits = LE_FLOWCTL_MAX_CREDITS - chan->tx_credits;
>         if (credits > max_credits) {
>                 BT_ERR("LE credits overflow");
> @@ -5923,11 +5929,21 @@ static inline void l2cap_le_sig_channel(struct l2cap_conn *conn,
>
>         BT_DBG("code 0x%2.2x len %d id 0x%2.2x", cmd->code, len, cmd->ident);
>
> -       if (len != skb->len || !cmd->ident) {
> +       if (len != skb->len) {
>                 BT_DBG("corrupted command");
>                 goto drop;
>         }
>
> +       if (!cmd->ident) {
> +               if (cmd->code != L2CAP_LE_CREDITS ||
> +                   len != sizeof(struct l2cap_le_credits))
> +                       goto drop;
> +
> +               /* Credits have no response or identifier-matched transaction. */
> +               l2cap_le_credits(conn, cmd, len, skb->data);
> +               goto drop;
> +       }
> +
>         err = l2cap_le_sig_cmd(conn, cmd, len, skb->data);
>         if (err) {
>                 struct l2cap_cmd_rej_unk rej;
>
> base-commit: 964430c038967fd06643e866f68115664e1a1bd1

Sashiko flagged a problem with this:

https://sashiko.dev/#/patchset/20261013031943.489829-1-cochcoder%40proton.me

-- 
Luiz Augusto von Dentz

[RFC PATCH v2] Bluetooth: L2CAP: tolerate zero-ident LE credit indications

[Kyle Pepper]

Tolerate exact-size, nonzero credit grants with identifier zero only
for connected LE credit-based channels. Keep the target and pending
security checks shared with ordinary identifiers. Do not send a
response with identifier zero or relax other signaling commands.

This is an interoperability exception to Core Vol 3 Part A section 4,
not a conformance fix.

Assisted-by: OpenCode:gpt-6.1-sol
Signed-off-by: Kyle Pepper <cochcoder@proton.me>
---
Changes since v1:
- Depend on the separately submitted target/state and pending-security fix.
- Require a connected ordinary LE CoC, an exact-size indication and a nonzero
  grant. Keep fixed/unready targets and ECRED identifier-zero grants excluded.
- Preserve shared target/security checks for normal and zero identifiers.
- Do not generate any response with identifier zero or relax other commands.

REQUIRED security dependency, submitted separately and not resent here:
https://lore.kernel.org/linux-bluetooth/20261015052018.129971-1-cochcoder@proton.me/
Signed dependency commit: 61a7ca610078ddf616873e7d4914cb6ac9eae7a3.
Apply it first. This mail includes its prerequisite patch-id against upstream
397464709a20. The resulting source tree matches the validated refreshed pair.

The Core specification still forbids identifier zero. This remains an
interoperability RFC requiring maintainer policy agreement, not a conformance
fix. The separate security patch is independently useful without this exception.

Fresh current-base controls: all nine focused security cases pass with either
security-only or combined kernels. Public credit controls pass 13/14 with
security-only (expected positive zero-ID failure), and 14/14 with this revision
added. No skips or captured KASAN/lockdep alerts occurred in these focused runs.
GCC W=1 changed objects and source-extracted security/target/zero-ID fixtures pass.

The refreshed full suite is NOT claimed passing: SCI Fast Mode encounters an
invalid response length for HCI opcode 0x20a3 and times out without a complete
summary. The same SCI failure reproduces on unpatched current upstream and both
revised guests. Initial spaced VM selectors selected broader tests; corrected
space-free credit runs are the focused results above. Earlier 134/134 combined
results belong to the older reference base, not this fresh full-suite attempt.

The combined Arch integration is reported working on hardware, not isolated
attribution or exhaustive device/security/teardown coverage. No remote CI pass
or severity claim is made. Private security reproducer/logs are not included.
Confirm archive rendering of the dependency link before sending.

 net/bluetooth/l2cap_core.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 7a7f30531..d805b1c62 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -5396,6 +5396,10 @@ static inline int l2cap_le_credits(struct l2cap_conn *conn,
 	     chan->mode != L2CAP_MODE_EXT_FLOWCTL))
 		goto unlock;
 
+	/* Tolerate identifier-zero credits only for a live LE CoC. */
+	if (!cmd->ident && (!credits || chan->mode != L2CAP_MODE_LE_FLOWCTL))
+		goto unlock;
+
 	max_credits = LE_FLOWCTL_MAX_CREDITS - chan->tx_credits;
 	if (credits > max_credits) {
 		BT_ERR("LE credits overflow");
@@ -5994,11 +5998,21 @@ static inline void l2cap_le_sig_channel(struct l2cap_conn *conn,
 
 	BT_DBG("code 0x%2.2x len %d id 0x%2.2x", cmd->code, len, cmd->ident);
 
-	if (len != skb->len || !cmd->ident) {
+	if (len != skb->len) {
 		BT_DBG("corrupted command");
 		goto drop;
 	}
 
+	if (!cmd->ident) {
+		if (cmd->code != L2CAP_LE_CREDITS ||
+		    len != sizeof(struct l2cap_le_credits))
+			goto drop;
+
+		/* Credits have no response or identifier-matched transaction. */
+		l2cap_le_credits(conn, cmd, len, skb->data);
+		goto drop;
+	}
+
 	err = l2cap_le_sig_cmd(conn, cmd, len, skb->data);
 	if (err) {
 		struct l2cap_cmd_rej_unk rej;

base-commit: 397464709a204da9b8dc3b01d6ea42539d951cd2
prerequisite-patch-id: 658bb8f3b3e38bbbb21f2619434affc641582b7f

RE: [RFC,v2] Bluetooth: L2CAP: tolerate zero-ident LE credit indications

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 851 bytes --]

This is an automated email and please do not reply to this email.

Dear Submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
While preparing the CI tests, the patches you submitted couldn't be applied to the current HEAD of the repository.

----- Output -----

error: patch failed: net/bluetooth/l2cap_core.c:5396
error: net/bluetooth/l2cap_core.c: patch does not apply
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"

Please resolve the issue and submit the patches again.


---
Regards,
Linux Bluetooth