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

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Message-ID: <10adcc89-6039-4b68-9206-360b7c3fff52@gmx.net>
Date: Tue, 29 Oct 2024 22:15:15 +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

Hi Jakub,

Am 29.10.24 um 20:10 schrieb Jakub Kicinski:
> On Tue, 22 Oct 2024 17:52:42 +0200 Stefan Wahren wrote:
>> -static int mse102x_tx_frame_spi(struct mse102x_net *mse, struct sk_buff *txp,
>> +static int mse102x_tx_frame_spi(struct mse102x_net *mse, struct sk_buff **txp,
>>   				unsigned int pad)
>>   {
>>   	struct mse102x_net_spi *mses = to_mse102x_spi(mse);
>> @@ -226,29 +226,29 @@ static int mse102x_tx_frame_spi(struct mse102x_net *mse, struct sk_buff *txp,
>>   	int ret;
>>
>>   	netif_dbg(mse, tx_queued, mse->ndev, "%s: skb %p, %d@%p\n",
>> -		  __func__, txp, txp->len, txp->data);
>> +		  __func__, *txp, (*txp)->len, (*txp)->data);
>>
>> -	if ((skb_headroom(txp) < DET_SOF_LEN) ||
>> -	    (skb_tailroom(txp) < DET_DFT_LEN + pad)) {
>> -		tskb = skb_copy_expand(txp, DET_SOF_LEN, DET_DFT_LEN + pad,
>> +	if ((skb_headroom(*txp) < DET_SOF_LEN) ||
>> +	    (skb_tailroom(*txp) < DET_DFT_LEN + pad)) {
>> +		tskb = skb_copy_expand(*txp, DET_SOF_LEN, DET_DFT_LEN + pad,
>>   				       GFP_KERNEL);
>>   		if (!tskb)
>>   			return -ENOMEM;
>>
>> -		dev_kfree_skb(txp);
>> -		txp = tskb;
>> +		dev_kfree_skb(*txp);
>> +		*txp = tskb;
>>   	}
>>
>> -	mse102x_push_header(txp);
>> +	mse102x_push_header(*txp);
>>
>>   	if (pad)
>> -		skb_put_zero(txp, pad);
>> +		skb_put_zero(*txp, pad);
>>
>> -	mse102x_put_footer(txp);
>> +	mse102x_put_footer(*txp);
>>
>> -	xfer->tx_buf = txp->data;
>> +	xfer->tx_buf = (*txp)->data;
>>   	xfer->rx_buf = NULL;
>> -	xfer->len = txp->len;
>> +	xfer->len = (*txp)->len;
>>
>>   	ret = spi_sync(mses->spidev, msg);
>>   	if (ret < 0) {
>> @@ -368,7 +368,7 @@ static void mse102x_rx_pkt_spi(struct mse102x_net *mse)
>>   	mse->ndev->stats.rx_bytes += rxlen;
> 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;
  }