CVE-2026-31513

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

Bluetooth: L2CAP: Fix stack-out-of-bounds read in l2cap_ecred_conn_req

Syzbot reported a KASAN stack-out-of-bounds read in l2cap_build_cmd()

that is triggered by a malformed Enhanced Credit Based Connection Request.

The vulnerability stems from l2cap_ecred_conn_req(). The function allocates

a local stack buffer (`pdu`) designed to hold a maximum of 5 Source Channel

IDs (SCIDs), totaling 18 bytes. When an attacker sends a request with more

than 5 SCIDs, the function calculates `rsp_len` based on this unvalidated

`cmd_len` before checking if the number of SCIDs exceeds

L2CAP_ECRED_MAX_CID.

If the SCID count is too high, the function correctly jumps to the

`response` label to reject the packet, but `rsp_len` retains the

attacker's oversized value. Consequently, l2cap_send_cmd() is instructed

to read past the end of the 18-byte `pdu` buffer, triggering a

KASAN panic.

Fix this by moving the assignment of `rsp_len` to after the `num_scid`

boundary check. If the packet is rejected, `rsp_len` will safely

remain 0, and the error response will only read the 8-byte base header

from the stack.