CVE-2026-31570

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

can: gw: fix OOB heap access in cgw_csum_crc8_rel()

cgw_csum_crc8_rel() correctly computes bounds-safe indices via calc_idx():

int from = calc_idx(crc8->from_idx, cf->len);
int to = calc_idx(crc8->to_idx, cf->len);
int res = calc_idx(crc8->result_idx, cf->len);

if (from < 0 || to < 0 || res < 0)
return;

However, the loop and the result write then use the raw s8 fields directly
instead of the computed variables:

for (i = crc8->from_idx; ...) /* BUG: raw negative index */
cf->data[crc8->result_idx] = ...; /* BUG: raw negative index */

With from_idx = to_idx = result_idx = -64 on a 64-byte CAN FD frame,
calc_idx(-64, 64) = 0 so the guard passes, but the loop iterates with
i = -64, reading cf->data[-64], and the write goes to cf->data[-64].
This write might end up to 56 (7.0-rc) or 40 (<= 6.19) bytes before the
start of the canfd_frame on the heap.

The companion function cgw_csum_xor_rel() uses `from`/`to`/`res`
correctly throughout; fix cgw_csum_crc8_rel() to match.

Confirmed with KASAN on linux-7.0-rc2:
BUG: KASAN: slab-out-of-bounds in cgw_csum_crc8_rel+0x515/0x5b0
Read of size 1 at addr ffff8880076619c8 by task poc_cgw_oob/62

To configure the can-gw crc8 checksums CAP_NET_ADMIN is needed.