Subject: Re: [PATCH] net: alteon: Add missing DMA mapping error checks in ace_start_xmit

From: Joe Damato <[email-masked]>
Date: Tue, 31 Mar 2026 16:43:22 -0700

On Tue, Mar 31, 2026 at 09:48:41AM +0800, Wang Jun wrote:
> The ace_start_xmit function does not check the return value of
> dma_map_page (via ace_map_tx_skb) and skb_frag_dma_map when building
> transmit descriptors. If mapping fails, an invalid DMA address is
> written to the descriptor, which may cause hardware to access
> illegal memory, leading to system instability or crashes.
> 
> Add proper dma_mapping_error() checks for all mapping calls. When
> mapping fails, free the skb, increment the dropped packet counter,
> and return NETDEV_TX_OK.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

Is this fixing a bug you've seen in the wild? If not, I'd probably drop the
fixes tag and send this to net-next instead.

> Cc: [email-masked]
> Signed-off-by: Wang Jun <[email-masked]>
> ---
>  drivers/net/ethernet/alteon/acenic.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/net/ethernet/alteon/acenic.c b/drivers/net/ethernet/alteon/acenic.c
> index 455ee8930824..acabede53663 100644
> --- a/drivers/net/ethernet/alteon/acenic.c
> +++ b/drivers/net/ethernet/alteon/acenic.c
> @@ -2417,6 +2417,11 @@ static netdev_tx_t ace_start_xmit(struct sk_buff *skb,
>  		u32 vlan_tag = 0;
>  
>  		mapping = ace_map_tx_skb(ap, skb, skb, idx);
> +		if (dma_mapping_error(&ap->pdev->dev, mapping)) {
> +			dev_kfree_skb(skb);
> +			dev->stats.tx_dropped++;
> +			return NETDEV_TX_OK;
> +		}
>  		flagsize = (skb->len << 16) | (BD_FLG_END);
>  		if (skb->ip_summed == CHECKSUM_PARTIAL)
>  			flagsize |= BD_FLG_TCP_UDP_SUM;
> @@ -2438,6 +2443,11 @@ static netdev_tx_t ace_start_xmit(struct sk_buff *skb,
>  		int i;
>  
>  		mapping = ace_map_tx_skb(ap, skb, NULL, idx);
> +		if (dma_mapping_error(&ap->pdev->dev, mapping)) {
> +			dev_kfree_skb(skb);
> +			dev->stats.tx_dropped++;
> +			return NETDEV_TX_OK;
> +		}

I am not sure about this. The function ace_map_tx_skb seems to modify a
tx_ring_info entry, possibly writing invalid state to it if the dma_map_page
fails?

Maybe a better fix would be to refactor ace_map_tx_skb and do the
dma_mapping_error check there and change the return type of the function and
the code flow?

Then you wouldn't need to duplicate the error path handling code.