Re: [PATCH net v2 1/1] net: ethernet: lantiq_etop: fix memory disclosure

[Florian Fainelli <f.fainelli@gmail.com>]

On 9/21/24 03:58, Aleksander Jan Bajkowski wrote:
> When applying padding, the buffer is not zeroed, which results in memory
> disclosure. The mentioned data is observed on the wire. This patch uses
> skb_put_padto() to pad Ethernet frames properly. The mentioned function
> zeroes the expanded buffer.
> 
> In case the packet cannot be padded it is silently dropped. Statistics
> are also not incremented. This driver does not support statistics in the
> old 32-bit format or the new 64-bit format. These will be added in the
> future. In its current form, the patch should be easily backported to
> stable versions.
> 
> Ethernet MACs on Amazon-SE and Danube cannot do padding of the packets
> in hardware, so software padding must be applied.
> 
> Fixes: 504d4721ee8e ("MIPS: Lantiq: Add ethernet driver")
> Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
> ---
>   drivers/net/ethernet/lantiq_etop.c | 11 ++++++-----
>   1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/lantiq_etop.c b/drivers/net/ethernet/lantiq_etop.c
> index 3c289bfe0a09..36f1e3c93ca5 100644
> --- a/drivers/net/ethernet/lantiq_etop.c
> +++ b/drivers/net/ethernet/lantiq_etop.c
> @@ -477,11 +477,11 @@ ltq_etop_tx(struct sk_buff *skb, struct net_device *dev)
>   	struct ltq_etop_priv *priv = netdev_priv(dev);
>   	struct ltq_etop_chan *ch = &priv->ch[(queue << 1) | 1];
>   	struct ltq_dma_desc *desc = &ch->dma.desc_base[ch->dma.desc];
> -	int len;
>   	unsigned long flags;
>   	u32 byte_offset;
>   
> -	len = skb->len < ETH_ZLEN ? ETH_ZLEN : skb->len;
> +	if (skb_put_padto(skb, ETH_ZLEN))
> +		return NETDEV_TX_OK;

You should consider continuing to use the temporary variable 'len' here, 
and just re-assign it after the call to skb_put_padto() and avoid 
introducing potential user-after-free near the point where you program 
the buffer length into the HW. This also minimizes the amount of lines 
to review.
-- 
Florian