[PATCH][next] netfilter: nf_tables: Fix dereference of null pointer flow

[PATCH][next] netfilter: nf_tables: Fix dereference of null pointer flow

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

In the case where chain->flags & NFT_CHAIN_HW_OFFLOAD is false then
nft_flow_rule_create is not called and flow is NULL. The subsequent
error handling execution via label err_destroy_flow_rule will lead
to a null pointer dereference on flow when calling nft_flow_rule_destroy.
Since the error path to err_destroy_flow_rule has to cater for null
and non-null flows, only call nft_flow_rule_destroy if flow is non-null
to fix this issue.

Addresses-Coverity: ("Explicity null dereference")
Fixes: 3c5e44622011 ("netfilter: nf_tables: memleak in hw offload abort path")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 net/netfilter/nf_tables_api.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 390d4466567f..de182d1f7c4e 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3446,7 +3446,8 @@ static int nf_tables_newrule(struct sk_buff *skb, const struct nfnl_info *info,
 	return 0;
 
 err_destroy_flow_rule:
-	nft_flow_rule_destroy(flow);
+	if (flow)
+		nft_flow_rule_destroy(flow);
 err_release_rule:
 	nf_tables_rule_release(&ctx, rule);
 err_release_expr:
-- 
2.31.1

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

[Dan Carpenter]

Btw, why is there no clean up if nft_table_validate() fails?

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.

  3445  
  3446          return 0;
  3447  
  3448  err_destroy_flow_rule:
  3449          nft_flow_rule_destroy(flow);
  3450  err_release_rule:
  3451          nf_tables_rule_release(&ctx, rule);
  3452  err_release_expr:
  3453          for (i = 0; i < n; i++) {
  3454                  if (expr_info[i].ops) {
  3455                          module_put(expr_info[i].ops->type->owner);
  3456                          if (expr_info[i].ops->type->release_ops)
  3457                                  expr_info[i].ops->type->release_ops(expr_info[i].ops);
  3458                  }
  3459          }
  3460          kvfree(expr_info);
  3461  
  3462          return err;
  3463  }

regards,
dan carpenter

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

[Pablo Neira Ayuso]

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.

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

[Dan Carpenter]

On Fri, Jun 25, 2021 at 12:20:21PM +0200, Pablo Neira Ayuso wrote:
> 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.
> 

Ah...  Thanks.

regards,
dan carpenter

AW: [PATCH][next] netfilter: nf_tables: Fix dereference of null pointer flow

[Walter Harms]

hi Colin,
most free_something_functions accept NULL
these days, perhaps it would be more efficient
to add a check in nft_flow_rule_destroy().
There is a chance that this will catch the same
mistake in future  also.

jm2c,
re,
 wh
________________________________________
Von: Colin King <colin.king@canonical.com>
Gesendet: Donnerstag, 24. Juni 2021 21:57:18
An: Pablo Neira Ayuso; Jozsef Kadlecsik; Florian Westphal; David S . Miller; Jakub Kicinski; netfilter-devel@vger.kernel.org; coreteam@netfilter.org; netdev@vger.kernel.org
Cc: kernel-janitors@vger.kernel.org; linux-kernel@vger.kernel.org
Betreff: [PATCH][next] netfilter: nf_tables: Fix dereference of null pointer flow

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From: Colin Ian King <colin.king@canonical.com>

In the case where chain->flags & NFT_CHAIN_HW_OFFLOAD is false then
nft_flow_rule_create is not called and flow is NULL. The subsequent
error handling execution via label err_destroy_flow_rule will lead
to a null pointer dereference on flow when calling nft_flow_rule_destroy.
Since the error path to err_destroy_flow_rule has to cater for null
and non-null flows, only call nft_flow_rule_destroy if flow is non-null
to fix this issue.

Addresses-Coverity: ("Explicity null dereference")
Fixes: 3c5e44622011 ("netfilter: nf_tables: memleak in hw offload abort path")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 net/netfilter/nf_tables_api.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 390d4466567f..de182d1f7c4e 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3446,7 +3446,8 @@ static int nf_tables_newrule(struct sk_buff *skb, const struct nfnl_info *info,
        return 0;

 err_destroy_flow_rule:
-       nft_flow_rule_destroy(flow);
+       if (flow)
+               nft_flow_rule_destroy(flow);
 err_release_rule:
        nf_tables_rule_release(&ctx, rule);
 err_release_expr:
--
2.31.1

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

[Pablo Neira Ayuso]

On Fri, Jun 25, 2021 at 10:06:26AM +0000, Walter Harms wrote:
> hi Colin,
> most free_something_functions accept NULL
> these days, perhaps it would be more efficient
> to add a check in nft_flow_rule_destroy().
> There is a chance that this will catch the same
> mistake in future  also.

I'm fine with Colin patch.

Thanks.

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

[Pablo Neira Ayuso]

On Thu, Jun 24, 2021 at 08:57:18PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> In the case where chain->flags & NFT_CHAIN_HW_OFFLOAD is false then
> nft_flow_rule_create is not called and flow is NULL. The subsequent
> error handling execution via label err_destroy_flow_rule will lead
> to a null pointer dereference on flow when calling nft_flow_rule_destroy.
> Since the error path to err_destroy_flow_rule has to cater for null
> and non-null flows, only call nft_flow_rule_destroy if flow is non-null
> to fix this issue.

Applied, thanks.