In the Linux kernel, the following vulnerability has been resolved: Bluetooth: L2CAP: Fix stack...

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.