linux-kernel - Re: [PATCH net] net: wwan: t7xx: off-by-one error in t7xx_dpmaif_rx_buf

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Message-ID: <34589bdb-8cbd-455d-9e5b-a237d5c2cd0c@gmail.com>
Date: Tue, 29 Oct 2024 01:55:29 +0200
From: Sergey Ryazanov <ryazanov.s.a@...il.com>
To: Jinjie Ruan <ruanjinjie@...wei.com>, chandrashekar.devegowda@...el.com,
 chiranjeevi.rapolu@...ux.intel.com, haijun.liu@...iatek.com,
 m.chetan.kumar@...ux.intel.com, ricardo.martinez@...ux.intel.com,
 loic.poulain@...aro.org, johannes@...solutions.net, andrew+netdev@...n.ch,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, ilpo.jarvinen@...ux.intel.com, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: wwan: t7xx: off-by-one error in
 t7xx_dpmaif_rx_buf_alloc()

Hello Jinjie,

On 28.10.2024 10:06, Jinjie Ruan wrote:
> The error path in t7xx_dpmaif_rx_buf_alloc(), free and unmap the already
> allocated and mapped skb in a loop, but the loop condition terminates when
> the index reaches zero, which fails to free the first allocated skb at
> index zero.
> 
> Check for >= 0 so that skb at index 0 is freed as well.

Nice catch! Still implementation needs some improvements, see below.

> 
> Fixes: d642b012df70 ("net: wwan: t7xx: Add data path interface")
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> ---
>   drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c b/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> index 210d84c67ef9..f2298330e05b 100644
> --- a/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> +++ b/drivers/net/wwan/t7xx/t7xx_hif_dpmaif_rx.c
> @@ -226,7 +226,7 @@ int t7xx_dpmaif_rx_buf_alloc(struct dpmaif_ctrl *dpmaif_ctrl,
>   	return 0;
>   
>   err_unmap_skbs:
> -	while (--i > 0)
> +	while (--i >= 0)
>   		t7xx_unmap_bat_skb(dpmaif_ctrl->dev, bat_req->bat_skb, i);

The index variable declared as unsigned so changing the condition alone 
will cause the endless loop. Can you change the variable type to signed 
as well?

--
Sergey