[PATCH net 5/9] can: netlink: fix IFLA_CAN_BITRATE_MAX attribute sizing

[Marc Kleine-Budde <mkl@pengutronix.de>]

From: Zhu Ling <zhuling0805@qq.com>

can_fill_info() emits IFLA_CAN_BITRATE_MAX with nla_put(), which consumes
space for both the attribute header and its aligned payload. However,
can_get_size() accounts for the payload only. The resulting underestimate
can make filling the netlink response fail with -EMSGSIZE when the skb has
no remaining slack.

Use nla_total_size() to account for the complete attribute.

Fixes: 2290aefa2e90 ("can: dev: Add support for limiting configured bitrate")
Cc: stable@vger.kernel.org
Signed-off-by: Zhu Ling <zhuling0805@qq.com>
Reviewed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://patch.msgid.link/tencent_D1C873B86B0E92011A264B0E196B911D5308@qq.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/bug/linux-3924d490-baed-49dc-880a-6fd1163cf08d
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---

Notes:
    FAQ:
    
    Q: What about netlink payload size underestimation in `can_pwm_get_size()`
       when PWM capabilities exist but `CAN_CTRLMODE_XL_TMS` is disabled?
    A: This issue will be fixed in a follow up patch, to ease backporting to
       stable.

 drivers/net/can/dev/netlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
index 0cd55613a616..c0367c9e65f4 100644
--- a/drivers/net/can/dev/netlink.c
+++ b/drivers/net/can/dev/netlink.c
@@ -825,7 +825,7 @@ static size_t can_get_size(const struct net_device *dev)
 	if (priv->bitrate_const)				/* IFLA_CAN_BITRATE_CONST */
 		size += nla_total_size(sizeof(*priv->bitrate_const) *
 				       priv->bitrate_const_cnt);
-	size += sizeof(priv->bitrate_max);			/* IFLA_CAN_BITRATE_MAX */
+	size += nla_total_size(sizeof(priv->bitrate_max));	/* IFLA_CAN_BITRATE_MAX */
 	size += can_ctrlmode_ext_get_size();			/* IFLA_CAN_CTRLMODE_EXT */
 
 	size += can_data_bittiming_get_size(dev, &priv->fd,
-- 
2.53.0