[PATCH] ax25: Fix potential deadlock on &ax25_list_lock

[PATCH] ax25: Fix potential deadlock on &ax25_list_lock

[Chengfeng Ye]

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@gmail.com>
---
 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

Re: [PATCH] ax25: Fix potential deadlock on &ax25_list_lock

[Simon Horman]

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@gmail.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@kernel.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
> 
> 

Re: [PATCH] ax25: Fix potential deadlock on &ax25_list_lock

[Jakub Kicinski]

On Sat, 30 Sep 2023 18:14:34 +0200 Simon Horman wrote:
> 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")

You must have mis-pasted this Fixes tag :)

Chengfend, please find the right Fixes tag and repost.
-- 
pw-bot: cr

Re: [PATCH] ax25: Fix potential deadlock on &ax25_list_lock

[Chengfeng Ye]

No problem, I just sent a v2 patch.

Thanks,
Chengfeng

Re: [PATCH] ax25: Fix potential deadlock on &ax25_list_lock

[Simon Horman]

On Wed, Oct 04, 2023 at 10:53:17AM -0700, Jakub Kicinski wrote:
> On Sat, 30 Sep 2023 18:14:34 +0200 Simon Horman wrote:
> > 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")
> 
> You must have mis-pasted this Fixes tag :)

Yes, sorry about that.

> Chengfend, please find the right Fixes tag and repost.