netdev - RE: [PATCH net-next] genetlink: fix policy dump for dumps

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Date:   Tue, 8 Nov 2022 23:49:10 +0000
From:   "Keller, Jacob E" <jacob.e.keller@...el.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        Jonathan Lemon <bsd@...a.com>
Subject: RE: [PATCH net-next] genetlink: fix policy dump for dumps



> -----Original Message-----
> From: Jakub Kicinski <kuba@...nel.org>
> Sent: Tuesday, November 8, 2022 3:44 PM
> To: Keller, Jacob E <jacob.e.keller@...el.com>
> Cc: davem@...emloft.net; netdev@...r.kernel.org; edumazet@...gle.com;
> pabeni@...hat.com; Jonathan Lemon <bsd@...a.com>
> Subject: Re: [PATCH net-next] genetlink: fix policy dump for dumps
> 
> On Tue, 8 Nov 2022 20:47:57 +0000 Keller, Jacob E wrote:
> > A little bit tricky code here, but it makes sense. We could rewrite this to be a bit
> more verbose like:
> >
> > doit_err = genl_get_cmd(.. GENL_CMD_CAP_DO ..);
> > dumpit_err = genl_get_cmd(.. GENL_CMD_CAP_DUMPIT ..);
> > if (doit_err && dumpit_err) {
> >   ...
> > }
> >
> > That might be a bit easier to read than the !! ( ) + ( ) < 1 notation.
> 
> True, I should not give into the bit math temptations.
> 
> How about a helper:
> 

Much better, the little explanation about the zero init helps too.

Thanks,
Jake

> diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
> index 9b7dfc45dd67..600993c80050 100644
> --- a/net/netlink/genetlink.c
> +++ b/net/netlink/genetlink.c
> @@ -282,6 +282,7 @@ genl_cmd_full_to_split(struct genl_split_ops *op,
>  	return 0;
>  }
> 
> +/* Must make sure that op is initialized to 0 on failure */
>  static int
>  genl_get_cmd(u32 cmd, u8 flags, const struct genl_family *family,
>  	     struct genl_split_ops *op)
> @@ -302,6 +303,21 @@ genl_get_cmd(u32 cmd, u8 flags, const struct
> genl_family *family,
>  	return err;
>  }
> 
> +/* For policy dumping only, get ops of both do and dump.
> + * Fail if both are missing, genl_get_cmd() will zero-init in case of failure.
> + */
> +static int
> +genl_get_cmd_both(u32 cmd, const struct genl_family *family,
> +		  struct genl_split_ops *doit, struct genl_split_ops *dumpit)
> +{
> +	int err1, err2;
> +
> +	err1 = genl_get_cmd(cmd, GENL_CMD_CAP_DO, family, doit);
> +	err2 = genl_get_cmd(cmd, GENL_CMD_CAP_DUMP, family, dumpit);
> +
> +	return err1 && err2 ? -ENOENT : 0;
> +}
> +
>  static bool
>  genl_op_iter_init(const struct genl_family *family, struct genl_op_iter *iter)
>  {
> @@ -1406,10 +1422,10 @@ static int ctrl_dumppolicy_start(struct
> netlink_callback *cb)
>  		ctx->single_op = true;
>  		ctx->op = nla_get_u32(tb[CTRL_ATTR_OP]);
> 
> -		if (genl_get_cmd(ctx->op, GENL_CMD_CAP_DO, rt, &doit) &&
> -		    genl_get_cmd(ctx->op, GENL_CMD_CAP_DUMP, rt, &dump)) {
> +		err = genl_get_cmd_both(ctx->op, rt, &doit, &dump);
> +		if (err) {
>  			NL_SET_BAD_ATTR(cb->extack, tb[CTRL_ATTR_OP]);
> -			return -ENOENT;
> +			return err;
>  		}
> 
>  		if (doit.policy) {
> @@ -1551,13 +1567,9 @@ static int ctrl_dumppolicy(struct sk_buff *skb, struct
> netlink_callback *cb)
>  		if (ctx->single_op) {
>  			struct genl_split_ops doit, dumpit;
> 
> -			if (genl_get_cmd(ctx->op, GENL_CMD_CAP_DO,
> -					 ctx->rt, &doit) &&
> -			    genl_get_cmd(ctx->op, GENL_CMD_CAP_DUMP,
> -					 ctx->rt, &dumpit)) {
> -				WARN_ON(1);
> +			if (WARN_ON(genl_get_cmd_both(ctx->op, ctx->rt,
> +						      &doit, &dumpit)))
>  				return -ENOENT;
> -			}
> 
>  			if (ctrl_dumppolicy_put_op(skb, cb, &doit, &dumpit))
>  				return skb->len;
> --
> 2.38.1