Re: [PATCH nf-next 1/3] netfilter: nf_tables: add generation mask to table objects

[Patrick McHardy <kaber@trash.net>]

On 04.08, Pablo Neira Ayuso wrote:
> The dumping of table objects can be inconsistent when interfering with the
> preparation phase of our 2-phase commit protocol because:
> 
> 1) We remove objects from the lists during the preparation phase, that can be
>    added re-added from the abort step. Thus, we may miss objects that are still
>    active.
> 
> 2) We add new objects to the lists during the preparation phase, so we may get
>    objects that are not yet active with an internal flag set.
> 
> We can resolve this problem with generation masks, as we already do for rules
> when we expose them to the packet path.
> 
> After this change, we always obtain a consistent list as long as we stay in the
> same generation. The userspace side can detect interferences through the
> generation counter. If so, it needs to restart.
> 
> As a result, we can get rid of the internal NFT_TABLE_INACTIVE flag.

I have a similar patch queued up, however there seems to be something missing
in this patch. The lookup functions need to take the genmask into account.
Otherwise you can not delete and add a new table in the same batch. The same
holds for all other object types.

> +static struct nft_table *nf_tables_table_lookup(struct net *net,
> +						const struct nft_af_info *afi,
> +						const struct nlattr *nla,
> +						bool trans)
>  {
>  	struct nft_table *table;
>  
> @@ -382,10 +411,10 @@ static struct nft_table *nf_tables_table_lookup(const struct nft_af_info *afi,
>  		return ERR_PTR(-EINVAL);
>  
>  	table = nft_table_lookup(afi, nla);
> -	if (table != NULL)
> -		return table;
> +	if (table == NULL || (trans && !nft_table_is_active_next(net, table)))
> +		return ERR_PTR(-ENOENT);

We really need to check the genid itself, in some cases we *only* want
currently active tables, f.i. gettable and dumps.