netdev - Re: [PATCH net] tg3: avoid double-freeing of rx data memory

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Date:	Wed, 6 Nov 2013 11:23:02 -0800
From:	"Michael Chan" <mchan@...adcom.com>
To:	"Ivan Vecera" <ivecera@...hat.com>
cc:	netdev@...r.kernel.org, davem@...emloft.net,
	"Nithin Nayak Sujir" <nsujir@...adcom.com>
Subject: Re: [PATCH net] tg3: avoid double-freeing of rx data memory

On Wed, 2013-11-06 at 14:02 +0100, Ivan Vecera wrote: 
> If build_skb fails the memory associated with the ring buffer is freed but
> the ri->data member is not zeroed in this case. This causes a double-free
> of this memory in tg3_free_rings->... path. The patch moves this block after
> setting ri->data to NULL.
> It would be nice to fix this bug also in stable >= v3.4 trees.

Good catch, thanks.  To be precise, the double free will only happen if
the ring is freed before the ring wraps around once.

Acked-by: Michael Chan <mchan@...adcom.com>

> 
> Cc: Nithin Nayak Sujir <nsujir@...adcom.com>
> Cc: Michael Chan <mchan@...adcom.com>
> Signed-off-by: Ivan Vecera <ivecera@...hat.com>
> ---
>  drivers/net/ethernet/broadcom/tg3.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
> index 12d961c..cd76d2a 100644
> --- a/drivers/net/ethernet/broadcom/tg3.c
> +++ b/drivers/net/ethernet/broadcom/tg3.c
> @@ -6848,12 +6848,6 @@ static int tg3_rx(struct tg3_napi *tnapi, int budget)
>  			pci_unmap_single(tp->pdev, dma_addr, skb_size,
>  					 PCI_DMA_FROMDEVICE);
>  
> -			skb = build_skb(data, frag_size);
> -			if (!skb) {
> -				tg3_frag_free(frag_size != 0, data);
> -				goto drop_it_no_recycle;
> -			}
> -			skb_reserve(skb, TG3_RX_OFFSET(tp));
>  			/* Ensure that the update to the data happens
>  			 * after the usage of the old DMA mapping.
>  			 */
> @@ -6861,6 +6855,12 @@ static int tg3_rx(struct tg3_napi *tnapi, int budget)
>  
>  			ri->data = NULL;
>  
> +			skb = build_skb(data, frag_size);
> +			if (!skb) {
> +				tg3_frag_free(frag_size != 0, data);
> +				goto drop_it_no_recycle;
> +			}
> +			skb_reserve(skb, TG3_RX_OFFSET(tp));
>  		} else {
>  			tg3_recycle_rx(tnapi, tpr, opaque_key,
>  				       desc_idx, *post_ptr);



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