linux-kernel - Re: [PATCH resent] drbd: Fix exception handling in nla_put_drbd_cfg

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Date:   Mon, 27 Mar 2023 14:28:37 +0200
From:   Christoph Böhmwalder 
        <christoph.boehmwalder@...bit.com>
To:     Markus Elfring <Markus.Elfring@....de>
Cc:     cocci@...ia.fr, LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org, drbd-dev@...ts.linbit.com,
        linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Philipp Reisner <philipp.reisner@...bit.com>
Subject: Re: [PATCH resent] drbd: Fix exception handling in
 nla_put_drbd_cfg_context()

Am 25.03.23 um 15:07 schrieb Markus Elfring:
> Date: Fri, 17 Mar 2023 18:32:05 +0100
> 
> The label “nla_put_failure” was used to jump to another pointer check
> despite of the detail in the implementation of the function
> “nla_put_drbd_cfg_context” that it was determined already that
> the corresponding variable contained a null pointer.
> 
> * Thus return directly after a call of the function
>   “nla_nest_start_noflag” failed.
> 
> * Delete an extra pointer check which became unnecessary
>   with this refactoring.
> 
> 
> This issue was detected by using the Coccinelle software.
> 
> Fixes: 543cc10b4cc5c60aa9fcc62705ccfb9998bf4697 ("drbd: drbd_adm_get_status needs to show some more detail")
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  drivers/block/drbd/drbd_nl.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
> index f49f2a5282e1..9cb947127472 100644
> --- a/drivers/block/drbd/drbd_nl.c
> +++ b/drivers/block/drbd/drbd_nl.c
> @@ -3187,7 +3187,7 @@ static int nla_put_drbd_cfg_context(struct sk_buff *skb,
>  	struct nlattr *nla;
>  	nla = nla_nest_start_noflag(skb, DRBD_NLA_CFG_CONTEXT);
>  	if (!nla)
> -		goto nla_put_failure;
> +		return -EMSGSIZE;
>  	if (device &&
>  	    nla_put_u32(skb, T_ctx_volume, device->vnr))
>  		goto nla_put_failure;
> @@ -3205,8 +3205,7 @@ static int nla_put_drbd_cfg_context(struct sk_buff *skb,
>  	return 0;
> 
>  nla_put_failure:
> -	if (nla)
> -		nla_nest_cancel(skb, nla);
> +	nla_nest_cancel(skb, nla);
>  	return -EMSGSIZE;
>  }
> 
> --
> 2.40.0
> 

Sorry, I fail to see how this is an improvement over the status quo,
much less a "fix".

Can you identify the issue with the current code and can you explain how
your patch makes it better?

-- 
Christoph Böhmwalder
LINBIT | Keeping the Digital World Running
DRBD HA —  Disaster Recovery — Software defined Storage