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

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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






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