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Message-ID: <ec046bcf-06ce-4abe-b0ea-b6741c9ff004@gmail.com>
Date: Mon, 23 Sep 2024 14:13:56 -0700
From: Florian Fainelli <f.fainelli@...il.com>
To: Aleksander Jan Bajkowski <olek2@...pl>, davem@...emloft.net,
edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
jacob.e.keller@...el.com, andrew@...n.ch, horms@...nel.org,
john@...ozen.org, ralph.hempel@...tiq.com, ralf@...ux-mips.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2 1/1] net: ethernet: lantiq_etop: fix memory
disclosure
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 <olek2@...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.
>
> 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
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