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Message-ID: <991dc2b6-12ef-458d-b37f-562c15a73a07@wp.pl>
Date: Mon, 23 Sep 2024 23:08:15 +0200
From: Aleksander Jan Bajkowski <olek2@...pl>
To: Florian Fainelli <f.fainelli@...il.com>, 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
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?
-->ltq_etop_tx()
|
| (dma irq fires)
|
-->ltq_etop_dma_irq()
|
| (napi task schedule)
|
-->ltq_etop_poll_tx()
|
|
|
-->dev_kfree_skb_any()
Regards
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