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netfilter: nf_tables: don't prevent event handler from device cleanup on netns exit

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When a netnsamespace exits, the nf_tables pernet_ops will remove all rules.
However, there is one caveat:

Base chains that register ingress hooks will cause use-after-free:
device is already gone at that point.

The device event handlers prevent this from happening:
netns exit synthesizes unregister events for all devices.

However, an improper fix for a race condition made the notifiers a no-op
in case they get called from netns exit path, so revert that part.

This is safe now as the previous patch fixed nf_tables pernet ops
and device notifier initialisation ordering.

Fixes: 0a2cf5ee43 ("netfilter: nf_tables: close race between netns exit and rmmod")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2018-08-02 21:44:41 +02:00 committed by Pablo Neira Ayuso
parent d209df3e7f
commit 6a48de0144
2 changed files with 9 additions and 10 deletions
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7
net/netfilter/nf_tables_api.c
View file

@ -5925,10 +5925,7 @@ static int nf_tables_flowtable_event(struct notifier_block *this,
if (event != NETDEV_UNREGISTER)
return 0;
net = maybe_get_net(dev_net(dev));
if (!net)
return 0;
net = dev_net(dev);
mutex_lock(&net->nft.commit_mutex);
list_for_each_entry(table, &net->nft.tables, list) {
list_for_each_entry(flowtable, &table->flowtables, list) {
@ -5936,7 +5933,7 @@ static int nf_tables_flowtable_event(struct notifier_block *this,
}
}
mutex_unlock(&net->nft.commit_mutex);
put_net(net);
return NOTIFY_DONE;
}

12
net/netfilter/nft_chain_filter.c
View file

@ -293,6 +293,13 @@ static void nft_netdev_event(unsigned long event, struct net_device *dev,
if (strcmp(basechain->dev_name, dev->name) != 0)
return;
/* UNREGISTER events are also happpening on netns exit.
*
* Altough nf_tables core releases all tables/chains, only
* this event handler provides guarantee that
* basechain.ops->dev is still accessible, so we cannot
* skip exiting net namespaces.
*/
__nft_release_basechain(ctx);
break;
case NETDEV_CHANGENAME:
@ -318,10 +325,6 @@ static int nf_tables_netdev_event(struct notifier_block *this,
event != NETDEV_CHANGENAME)
return NOTIFY_DONE;
ctx.net = maybe_get_net(ctx.net);
if (!ctx.net)
return NOTIFY_DONE;
mutex_lock(&ctx.net->nft.commit_mutex);
list_for_each_entry(table, &ctx.net->nft.tables, list) {
if (table->family != NFPROTO_NETDEV)
@ -338,7 +341,6 @@ static int nf_tables_netdev_event(struct notifier_block *this,
}
}
mutex_unlock(&ctx.net->nft.commit_mutex);
put_net(ctx.net);
return NOTIFY_DONE;
}