linux-kernel - Re: [PATCH] ax25: Fix potential deadlock on &ax25_list

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Date:   Sat, 30 Sep 2023 18:14:34 +0200
From:   Simon Horman <horms@...nel.org>
To:     Chengfeng Ye <dg573847474@...il.com>
Cc:     jreuter@...na.de, ralf@...ux-mips.org, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        linux-hams@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ax25: Fix potential deadlock on &ax25_list_lock

On Tue, Sep 26, 2023 at 10:57:32AM +0000, Chengfeng Ye wrote:
> Timer interrupt ax25_ds_timeout() could introduce double locks on
> &ax25_list_lock.
> 
> ax25_ioctl()
> --> ax25_ctl_ioctl()
> --> ax25_dama_off()
> --> ax25_dev_dama_off()
> --> ax25_check_dama_slave()
> --> spin_lock(&ax25_list_lock)
> <timer interrupt>
>    --> ax25_ds_timeout()
>    --> spin_lock(&ax25_list_lock)
> 
> This flaw was found by an experimental static analysis tool I am
> developing for irq-related deadlock.
> 
> To prevent the potential deadlock, the patch use spin_lock_bh()
> on &ax25_list_lock inside ax25_check_dama_slave().
> 
> Signed-off-by: Chengfeng Ye <dg573847474@...il.com>

Hi Chengfeng Ye,

thanks for your patch.

As a fix for Networking this should probably be targeted at the
'net' tree. Which should be denoted in the subject.

        Subject: [PATCH net] ...

And as a fix this patch should probably have a Fixes tag.
This ones seem appropriate to me, but I could be wrong.

Fixes: c070e51db5e2 ("ice: always add legacy 32byte RXDID in supported_rxdids")

I don't think it is necessary to repost just to address these issues,
but the Networking maintainers may think otherwise.

The code change itself looks good to me.

Reviewed-by: Simon Horman <horms@...nel.org>

> ---
>  net/ax25/ax25_ds_subr.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ax25/ax25_ds_subr.c b/net/ax25/ax25_ds_subr.c
> index f00e27df3c76..010b11303d32 100644
> --- a/net/ax25/ax25_ds_subr.c
> +++ b/net/ax25/ax25_ds_subr.c
> @@ -156,13 +156,13 @@ static int ax25_check_dama_slave(ax25_dev *ax25_dev)
>  	ax25_cb *ax25;
>  	int res = 0;
>  
> -	spin_lock(&ax25_list_lock);
> +	spin_lock_bh(&ax25_list_lock);
>  	ax25_for_each(ax25, &ax25_list)
>  		if (ax25->ax25_dev == ax25_dev && (ax25->condition & AX25_COND_DAMA_MODE) && ax25->state > AX25_STATE_1) {
>  			res = 1;
>  			break;
>  		}
> -	spin_unlock(&ax25_list_lock);
> +	spin_unlock_bh(&ax25_list_lock);
>  
>  	return res;
>  }
> -- 
> 2.17.1
> 
>