[PATCH 6.1 093/312] can: gw: fix OOB heap access in cgw_csum_crc8_rel()

Greg Kroah-Hartman
2026-04-08T18:12:16Z

From: Ali Norouzi <ali.norouzi@keysight.com>

commit b9c310d72783cc2f30d103eed83920a5a29c671a upstream.

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.

Fixes: 456a8a646b25 ("can: gw: add support for CAN FD frames")
Cc: stable@vger.kernel.org
Reported-by: Ali Norouzi <ali.norouzi@keysight.com>
Reviewed-by: Oliver Hartkopp <socketcan@hartkopp.net>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Ali Norouzi <ali.norouzi@keysight.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20260319-fix-can-gw-and-can-isotp-v2-1-c45d52c6d2d8@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/can/gw.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/can/gw.c
+++ b/net/can/gw.c
@@ -374,10 +374,10 @@ static void cgw_csum_crc8_rel(struct can
return;

if (from <= to) {
- for (i = crc8->from_idx; i <= crc8->to_idx; i++)
+ for (i = from; i <= to; i++)
crc = crc8->crctab[crc ^ cf->data[i]];
} else {
- for (i = crc8->from_idx; i >= crc8->to_idx; i--)
+ for (i = from; i >= to; i--)
crc = crc8->crctab[crc ^ cf->data[i]];
}

@@ -396,7 +396,7 @@ static void cgw_csum_crc8_rel(struct can
break;
}

- cf->data[crc8->result_idx] = crc ^ crc8->final_xor_val;
+ cf->data[res] = crc ^ crc8->final_xor_val;
}

static void cgw_csum_crc8_pos(struct canfd_frame *cf,