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>
Remove echo_skb_max rounding as this may increase it to unexpected values. In this sense restore echo_skb_max handling logic prior to commit 8256e0ca6010 ("can: kvaser_pciefd: Fix echo_skb race").
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 ---
Actually the trick with rounding up allows to calculate seq numbers efficiently, avoiding a more consuming 'mod' operation used in the current patch.
I see tx max size definitely matters only 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 size into account. The only downside is that the size of echo_skb[] should correspond to the max seq number (not tx max number), so in some situations a bit more memory would be consumed than could be.
So another approach to fix the problem would be to precompute the rounded up value of echo_skb_max and pass it to alloc_candev() making the size of the underlying echo_skb[] sufficient.
If that looks more acceptable, I'll be glad to rework the patch in that direction.
drivers/net/can/kvaser_pciefd.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/drivers/net/can/kvaser_pciefd.c b/drivers/net/can/kvaser_pciefd.c index f6921368cd14..1ec4ab9510b6 100644 --- a/drivers/net/can/kvaser_pciefd.c +++ b/drivers/net/can/kvaser_pciefd.c @@ -411,7 +411,6 @@ struct kvaser_pciefd_can { void __iomem *reg_base; struct can_berr_counter bec; u8 cmd_seq; - u8 tx_max_count; u8 tx_idx; u8 ack_idx; int err_rep_cnt; @@ -760,7 +759,7 @@ static int kvaser_pciefd_stop(struct net_device *netdev)
static unsigned int kvaser_pciefd_tx_avail(const struct kvaser_pciefd_can *can) { - return can->tx_max_count - (READ_ONCE(can->tx_idx) - READ_ONCE(can->ack_idx)); + return can->can.echo_skb_max - (READ_ONCE(can->tx_idx) - READ_ONCE(can->ack_idx)); }
static int kvaser_pciefd_prepare_tx_packet(struct kvaser_pciefd_tx_packet *p, @@ -810,7 +809,7 @@ static netdev_tx_t kvaser_pciefd_start_xmit(struct sk_buff *skb, { struct kvaser_pciefd_can *can = netdev_priv(netdev); struct kvaser_pciefd_tx_packet packet; - unsigned int seq = can->tx_idx & (can->can.echo_skb_max - 1); + unsigned int seq = can->tx_idx % can->can.echo_skb_max; unsigned int frame_len; int nr_words;
@@ -992,10 +991,9 @@ static int kvaser_pciefd_setup_can_ctrls(struct kvaser_pciefd *pcie) tx_nr_packets_max = FIELD_GET(KVASER_PCIEFD_KCAN_TX_NR_PACKETS_MAX_MASK, ioread32(can->reg_base + KVASER_PCIEFD_KCAN_TX_NR_PACKETS_REG)); - can->tx_max_count = min(KVASER_PCIEFD_CAN_TX_MAX_COUNT, tx_nr_packets_max - 1); + can->can.echo_skb_max = 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; @@ -1523,7 +1521,7 @@ static int kvaser_pciefd_handle_ack_packet(struct kvaser_pciefd *pcie, unsigned int len, frame_len = 0; struct sk_buff *skb;
- if (echo_idx != (can->ack_idx & (can->can.echo_skb_max - 1))) + if (echo_idx != can->ack_idx % can->can.echo_skb_max) return 0; skb = can->can.echo_skb[echo_idx]; if (!skb)