CVE-2026-72333: Bluetooth: L2CAP: fix tx ident leak for commands without a response

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: L2CAP: fix tx ident leak for commands without a response

Commit 6c3ea155e5ee ("Bluetooth: L2CAP: Fix not tracking outstanding TX ident") changed ident allocation to use an IDA, releasing idents in l2capputident() when the matching response command is received.

But identifiers allocated for commands that have no response defined are never released. In particular L2CAPLECREDITS is sent repeatedly for the lifetime of an LE CoC channel, so a peer streaming data to the host exhausts the 1-255 ident range after 254 credit packets. From then on l2capgetident() fails:

kernel: Bluetooth: Unable to allocate ident: -28

and every subsequent L2CAPLECREDITS packet is sent with ident 0, which is invalid (Core Spec, Vol 3, Part A, Section 4: "Signaling identifier 0x00 is an invalid identifier and shall never be used in any command"). Remote stacks that validate the ident drop these commands, never receive new credits, and the channel stalls permanently. With default socket buffers this happens after roughly 0.5 MB of received data (the exact amount depends on the socket receive buffer):

< ACL Data TX: Handle 2048 flags 0x00 dlen 12 LE L2CAP: LE Flow Control Credit (0x16) ident 0 len 4 Source CID: 64 Credits: 1

Release the ident immediately after sending L2CAPLECREDITS since no response will ever release it. Use a local variable instead of chan->ident so that an ident that an EXTFLOWCTL channel may be waiting on (e.g. a pending reconfigure) is not overwritten by a credit packet.

Also add the missing L2CAPLECONNRSP case to l2capputident() so idents allocated for outgoing L2CAPLECONNREQ commands are released when the response arrives.