[RFC PATCH v3 2/2] 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@xxxxxxxxx>
---
Changes since v2:
- Include the unchanged security prerequisite as patch 1/2 in this series,
  rather than relying on CI to apply a separately submitted dependency.
- Refresh onto bluetooth-next ff8b09806b7b without a source delta.
- Wrap test notes to keep all prose within GitLint's 80-column limit.

The saved v2 report failed application at l2cap_core.c:5396. That patch
depends on the security fix, which was not yet upstream. A dependency
link and prerequisite-patch-id did not make that CI run apply it first.
Apply this entire series in order; patch 2 alone is not a valid input.

The Core specification still forbids identifier zero. This remains an
interoperability RFC requiring maintainer policy agreement, not a
conformance fix. Patch 1 is independently useful without this exception.

Earlier 397464709a20 runs passed all nine focused security controls with
security-only and combined guests. Public credit controls passed 13/14
security-only (expected positive zero-ID failure), 14/14 combined, with
no skips or captured kernel alerts. Source-extracted fixtures and GCC
W=1 changed objects passed. These are prior runs, not fresh v3 VMs.

The earlier full-suite attempt was incomplete due to an SCI timeout also
seen on the unpatched base. No fresh full-suite or remote CI pass is
claimed for v3. The combined Arch trial is reported working on hardware,
not isolated attribution or exhaustive device/security/teardown coverage.
Private security reproducer/logs and the archived BlueZ test companion
are excluded. This series contains only the two kernel patches.

 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;