netdev - Re: [PATCH net] net: vertexcom: mse102x: Fix possible double free of TX skb

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Message-ID: <ea4842c2-7c65-4d45-9964-1a1274d29ea4@gmx.net>
Date: Wed, 30 Oct 2024 00:06:46 +0100
From: Stefan Wahren <wahrenst@....net>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, Dan Carpenter <dan.carpenter@...aro.org>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org, Simon Horman <horms@...nel.org>
Subject: Re: [PATCH net] net: vertexcom: mse102x: Fix possible double free of
 TX skb

Am 29.10.24 um 23:01 schrieb Jakub Kicinski:
> On Tue, 29 Oct 2024 22:15:15 +0100 Stefan Wahren wrote:
>>> Isn't it easier to change this function to free the copy rather than
>>> the original? That way the original will remain valid for the callers.
>> You mean something like this?
>>
>> diff --git a/drivers/net/ethernet/vertexcom/mse102x.c
>> b/drivers/net/ethernet/vertexcom/mse102x.c
>> index a04d4073def9..2c37957478fb 100644
>> --- a/drivers/net/ethernet/vertexcom/mse102x.c
>> +++ b/drivers/net/ethernet/vertexcom/mse102x.c
>> @@ -222,7 +222,7 @@ static int mse102x_tx_frame_spi(struct mse102x_net
>> *mse, struct sk_buff *txp,
>>        struct mse102x_net_spi *mses = to_mse102x_spi(mse);
>>        struct spi_transfer *xfer = &mses->spi_xfer;
>>        struct spi_message *msg = &mses->spi_msg;
>> -    struct sk_buff *tskb;
>> +    struct sk_buff *tskb = NULL;
>>        int ret;
>>
>>        netif_dbg(mse, tx_queued, mse->ndev, "%s: skb %p, %d@%p\n",
>> @@ -235,7 +235,6 @@ static int mse102x_tx_frame_spi(struct mse102x_net
>> *mse, struct sk_buff *txp,
>>            if (!tskb)
>>                return -ENOMEM;
>>
>> -        dev_kfree_skb(txp);
>>            txp = tskb;
>>        }
>>
>> @@ -257,6 +256,8 @@ static int mse102x_tx_frame_spi(struct mse102x_net
>> *mse, struct sk_buff *txp,
>>            mse->stats.xfer_err++;
>>        }
>>
>> +    dev_kfree_skb(tskb);
>> +
>>        return ret;
>>    }
> Exactly, I think it would work and it feels simpler.
I didn't test it yet, i need access to evaluation board before. But this
change will behave differently regarding stats of tx_bytes [1]. The
first version will include the padding, while the second does not.

[1] -
https://elixir.bootlin.com/linux/v6.12-rc5/source/drivers/net/ethernet/vertexcom/mse102x.c#L445