echo_skb_max should define the supported upper limit of echo_skb[] allocated inside the netdevice's priv. The corresponding size value provided by this driver to alloc_candev() is KVASER_PCIEFD_CAN_TX_MAX_COUNT which is 17.

But later echo_skb_max is rounded up to the nearest power of two (for the max case, that would be 32) and the tx/ack indices calculated further during tx/rx may exceed the upper array boundary. Kasan reported this for the ack case inside kvaser_pciefd_handle_ack_packet(), though the xmit function has actually caught the same thing earlier.

BUG: KASAN: slab-out-of-bounds in kvaser_pciefd_handle_ack_packet+0x2d7/0x92a drivers/net/can/kvaser_pciefd.c:1528 Read of size 8 at addr ffff888105e4f078 by task swapper/4/0

CPU: 4 UID: 0 PID: 0 Comm: swapper/4 Not tainted 6.15.0 #12 PREEMPT(voluntary) Call Trace: <IRQ> dump_stack_lvl lib/dump_stack.c:122 print_report mm/kasan/report.c:521 kasan_report mm/kasan/report.c:634 kvaser_pciefd_handle_ack_packet drivers/net/can/kvaser_pciefd.c:1528 kvaser_pciefd_read_packet drivers/net/can/kvaser_pciefd.c:1605 kvaser_pciefd_read_buffer drivers/net/can/kvaser_pciefd.c:1656 kvaser_pciefd_receive_irq drivers/net/can/kvaser_pciefd.c:1684 kvaser_pciefd_irq_handler drivers/net/can/kvaser_pciefd.c:1733 __handle_irq_event_percpu kernel/irq/handle.c:158 handle_irq_event kernel/irq/handle.c:210 handle_edge_irq kernel/irq/chip.c:833 __common_interrupt arch/x86/kernel/irq.c:296 common_interrupt arch/x86/kernel/irq.c:286 </IRQ>

Tx max count definitely matters for kvaser_pciefd_tx_avail(), but for seq numbers' generation that's not the case - we're free to calculate them as would be more convenient, not taking tx max count into account. The only downside is that the size of echo_skb[] should correspond to the max seq number (not tx max count), so in some situations a bit more memory would be consumed than could be.

Thus make the size of the underlying echo_skb[] sufficient for the rounded max tx value.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 8256e0ca6010 ("can: kvaser_pciefd: Fix echo_skb race") Cc: stable@vger.kernel.org Signed-off-by: Fedor Pchelkin pchelkin@ispras.ru ---

v2: fix the problem by rounding up the KVASER_PCIEFD_CAN_TX_MAX_COUNT constant when allocating candev (Axel Forsman)

drivers/net/can/kvaser_pciefd.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/can/kvaser_pciefd.c b/drivers/net/can/kvaser_pciefd.c index f6921368cd14..0071a51ce2c1 100644 --- a/drivers/net/can/kvaser_pciefd.c +++ b/drivers/net/can/kvaser_pciefd.c @@ -966,7 +966,7 @@ static int kvaser_pciefd_setup_can_ctrls(struct kvaser_pciefd *pcie) u32 status, tx_nr_packets_max;

netdev = alloc_candev(sizeof(struct kvaser_pciefd_can), - KVASER_PCIEFD_CAN_TX_MAX_COUNT); + roundup_pow_of_two(KVASER_PCIEFD_CAN_TX_MAX_COUNT)); if (!netdev) return -ENOMEM;

@@ -995,7 +995,6 @@ static int kvaser_pciefd_setup_can_ctrls(struct kvaser_pciefd *pcie) can->tx_max_count = min(KVASER_PCIEFD_CAN_TX_MAX_COUNT, tx_nr_packets_max - 1);

can->can.clock.freq = pcie->freq; - can->can.echo_skb_max = roundup_pow_of_two(can->tx_max_count); spin_lock_init(&can->lock);

can->can.bittiming_const = &kvaser_pciefd_bittiming_const;