From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Su Yanjun <suyanjun218@163.com>
Cc: kadlec@blackhole.kfki.hu, fw@strlen.de, davem@davemloft.net,
netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
suyj.fnst@cn.fujitsu.com
Subject: Re: [PATCH] netfilter: nf_ct_helper: Fix possible panic when nf_conntrack_helper_unregister is used in an unloadable module
Date: Fri, 8 Mar 2019 16:59:34 +0100 [thread overview]
Message-ID: <20190308155934.vfx2ah4k4guqvhyu@salvia> (raw)
In-Reply-To: <1551419766-1039-1-git-send-email-suyanjun218@163.com>
On Fri, Mar 01, 2019 at 01:56:06PM +0800, Su Yanjun wrote:
> From: Su Yanjun <suyj.fnst@cn.fujitsu.com>
>
> Because nf_conntrack_helper_unregister maybe used in an unloadable module,
> it uses 'synchronize_rcu' which may cause kernel panic.
>
> According to the artical:
> RCU and Unloadable Modules
> https://lwn.net/Articles/217484/
>
> When we have a heavy rcu callback load, then some of the callbacks might be
> deferred in order to allow other processing to proceed. sychnorize_rcu does
> not wait rcu callback complete and module may be unloaded before callback
> done.
>
> This patch uses rcu_barrier instead of synchronize_rcu will prevent this
> situation.
>
> Signed-off-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
> ---
> net/netfilter/nf_conntrack_helper.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
> index 274baf1..0ee9378 100644
> --- a/net/netfilter/nf_conntrack_helper.c
> +++ b/net/netfilter/nf_conntrack_helper.c
> @@ -397,8 +397,15 @@ void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
>
> /* Make sure every nothing is still using the helper unless its a
> * connection in the hash.
> + *
> + * 'synchronize_rcu' may have problem when rcu callback function
> + * is used in unloadable modules. Use rcu_barrier instead, so that
> + * it will wait until rcu callback completes before modules are
> + * unloaded.
> + * More detail about rcu_barrier please see:
> + * https://lwn.net/Articles/217484/
> */
> - synchronize_rcu();
> + rcu_barrier();
Are you sure this is correct?
IIRC rcu_barrier() makes sure no pending callback is still waiting in
the queue to run. We have don't use call_rcu() in this code, which is
what rcu_barrier() is meant for.
Please correct me if I'm mistaken.
Thanks!
>
> nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
> nf_ct_iterate_destroy(unhelp, me);
> @@ -406,7 +413,7 @@ void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
> /* Maybe someone has gotten the helper already when unhelp above.
> * So need to wait it.
> */
> - synchronize_rcu();
> + rcu_barrier();
> }
> EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
>
> --
> 2.7.4
>
>
next prev parent reply other threads:[~2019-03-08 15:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-01 5:56 [PATCH] netfilter: nf_ct_helper: Fix possible panic when nf_conntrack_helper_unregister is used in an unloadable module Su Yanjun
2019-03-01 8:43 ` Sergei Shtylyov
2019-03-01 9:08 ` Su Yanjun <suyj.fnst@cn.fujitsu.com>
2019-03-08 15:59 ` Pablo Neira Ayuso [this message]
2019-03-14 3:20 ` Su Yanjun <suyj.fnst@cn.fujitsu.com>
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