[PATCH net-next v1] net: mvneta: Avoid the misuse of the '_t' variants

[PATCH net-next v1] net: mvneta: Avoid the misuse of the '_t' variants

[Yan Zhen]

Type conversions (especially when narrowing down types) can lead to 
unexpected behavior and should be done with extreme caution.

In this case if someone tries to set the tx_pending to 65536(0x10000),
after forcing it to convert to u16, it becomes 0x0000, they will get
the minimum supported size and not the maximum.

Based on previous discussions [1], such behavior may confuse users or even
create unexpected errors.

[1] https://lore.kernel.org/netdev/d23dfbf563714d7090d163a075ca9a51@AcuMS.aculab.com/

Signed-off-by: Yan Zhen <yanzhen@vivo.com>
---
 drivers/net/ethernet/marvell/mvneta.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index d72b2d5f96db..b41de182cc88 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -4753,8 +4753,8 @@ mvneta_ethtool_set_ringparam(struct net_device *dev,
 	pp->rx_ring_size = ring->rx_pending < MVNETA_MAX_RXD ?
 		ring->rx_pending : MVNETA_MAX_RXD;
 
-	pp->tx_ring_size = clamp_t(u16, ring->tx_pending,
-				   MVNETA_MAX_SKB_DESCS * 2, MVNETA_MAX_TXD);
+	pp->tx_ring_size = clamp(ring->tx_pending,
+				 MVNETA_MAX_SKB_DESCS * 2, MVNETA_MAX_TXD);
 	if (pp->tx_ring_size != ring->tx_pending)
 		netdev_warn(dev, "TX queue size set to %u (requested %u)\n",
 			    pp->tx_ring_size, ring->tx_pending);
-- 
2.34.1

RE: [PATCH net-next v1] net: mvneta: Avoid the misuse of the '_t' variants

[David Laight]

From: Yan Zhen
> Sent: 05 September 2024 07:37
> 
> Type conversions (especially when narrowing down types) can lead to
> unexpected behavior and should be done with extreme caution.
> 
> In this case if someone tries to set the tx_pending to 65536(0x10000),
> after forcing it to convert to u16, it becomes 0x0000, they will get
> the minimum supported size and not the maximum.
> 
> Based on previous discussions [1], such behavior may confuse users or even
> create unexpected errors.
> 
> [1] https://lore.kernel.org/netdev/d23dfbf563714d7090d163a075ca9a51@AcuMS.aculab.com/
> 
> Signed-off-by: Yan Zhen <yanzhen@vivo.com>

Reviewed-by: david.laight@aculab.com

> ---
>  drivers/net/ethernet/marvell/mvneta.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index d72b2d5f96db..b41de182cc88 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -4753,8 +4753,8 @@ mvneta_ethtool_set_ringparam(struct net_device *dev,
>  	pp->rx_ring_size = ring->rx_pending < MVNETA_MAX_RXD ?
>  		ring->rx_pending : MVNETA_MAX_RXD;
> 
> -	pp->tx_ring_size = clamp_t(u16, ring->tx_pending,
> -				   MVNETA_MAX_SKB_DESCS * 2, MVNETA_MAX_TXD);
> +	pp->tx_ring_size = clamp(ring->tx_pending,
> +				 MVNETA_MAX_SKB_DESCS * 2, MVNETA_MAX_TXD);
>  	if (pp->tx_ring_size != ring->tx_pending)
>  		netdev_warn(dev, "TX queue size set to %u (requested %u)\n",
>  			    pp->tx_ring_size, ring->tx_pending);
> --
> 2.34.1

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH net-next v1] net: mvneta: Avoid the misuse of the '_t' variants

[Jakub Kicinski]

On Thu,  5 Sep 2024 14:36:45 +0800 Yan Zhen wrote:
> In this case if someone tries to set the tx_pending to 65536(0x10000),
> after forcing it to convert to u16, it becomes 0x0000, they will get
> the minimum supported size and not the maximum.

Core validates against tx_max_pending before calling the driver.
-- 
pw-bot: reject