linux-kernel - Re: [PATCH][next] netfilter: nf_tables: Fix dereference of null pointer flow

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Date:   Fri, 25 Jun 2021 12:20:21 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Colin King <colin.king@...onical.com>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] netfilter: nf_tables: Fix dereference of null
 pointer flow

Hi,

On Fri, Jun 25, 2021 at 12:59:01PM +0300, Dan Carpenter wrote:
> Btw, why is there no clean up if nft_table_validate() fails?

See below.

> net/netfilter/nf_tables_api.c
>   3432                                  list_add_tail_rcu(&rule->list, &old_rule->list);
>   3433                          else
>   3434                                  list_add_rcu(&rule->list, &chain->rules);
>   3435                  }
>   3436          }
>   3437          kvfree(expr_info);
>   3438          chain->use++;
>   3439  
>   3440          if (flow)
>   3441                  nft_trans_flow_rule(trans) = flow;
>   3442  
>   3443          if (nft_net->validate_state == NFT_VALIDATE_DO)
>   3444                  return nft_table_validate(net, table);
>                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> The cleanup for this would be quite involved unfortunately...  Not
> necessarily something to attempt without being able to test the code.

At this stage, the transaction has been already registered in the
list, and the nf_tables_abort() path takes care of undoing what has
been updated in the preparation phase.

Having said this, Colin patch is correct, it's fixing up the error
path.