CVE-2026-31772

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

Bluetooth: hci_sync: fix stack buffer overflow in hci_le_big_create_sync

hci_le_big_create_sync() uses DEFINE_FLEX to allocate a

struct hci_cp_le_big_create_sync on the stack with room for 0x11 (17)

BIS entries. However, conn->num_bis can hold up to HCI_MAX_ISO_BIS (31)

entries — validated against ISO_MAX_NUM_BIS (0x1f) in the caller

hci_conn_big_create_sync(). When conn->num_bis is between 18 and 31,

the memcpy that copies conn->bis into cp->bis writes up to 14 bytes

past the stack buffer, corrupting adjacent stack memory.

This is trivially reproducible: binding an ISO socket with

bc_num_bis = ISO_MAX_NUM_BIS (31) and calling listen() will

eventually trigger hci_le_big_create_sync() from the HCI command

sync worker, causing a KASAN-detectable stack-out-of-bounds write:

BUG: KASAN: stack-out-of-bounds in hci_le_big_create_sync+0x256/0x3b0

Write of size 31 at addr ffffc90000487b48 by task kworker/u9:0/71

Fix this by changing the DEFINE_FLEX count from the incorrect 0x11 to

HCI_MAX_ISO_BIS, which matches the maximum number of BIS entries that

conn->bis can actually carry.