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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/23/24 14:08, Aleksander Jan Bajkowski wrote: > Hi Florian, > > > On 23.09.2024 20:21, Florian Fainelli wrote: >> 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 >>> --- >>>   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. > > To the best of my knowledge, the skb is not released until the DMA > finishes the transfer. > Then the ltq_etop_poll_tx() function is called, which releases the skb. > Can you explain > what sequence of events can lead to a use-after-free error? There is none right now, but assuming you might add byte queue limits in the future, or just re-structure the code, reading from skb->len is error prone and is better left avoided, especially since this will result in few lines being changed in your case. > > -->ltq_etop_tx() >      | >      | (dma irq fires) >      | >      -->ltq_etop_dma_irq() >           | >           | (napi task schedule) >           | >           -->ltq_etop_poll_tx() >                | >                | >                | >                -->dev_kfree_skb_any() > > Regards > -- Florian