From mboxrd@z Thu Jan 1 00:00:00 1970 From: Flavio Leitner Subject: Re: [PATCH] netfilter: check if the socket netns is correct. Date: Thu, 27 Sep 2018 19:58:24 -0300 Message-ID: <20180927225824.GT2702@plex.lan> References: <20180927204629.GA4680@roeck-us.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Pablo Neira Ayuso , Jozsef Kadlecsik , Florian Westphal , "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Guenter Roeck Return-path: Content-Disposition: inline In-Reply-To: <20180927204629.GA4680@roeck-us.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org On Thu, Sep 27, 2018 at 01:46:29PM -0700, Guenter Roeck wrote: > Hi Flavio, > > On Wed, Jun 27, 2018 at 10:34:25AM -0300, Flavio Leitner wrote: > > Netfilter assumes that if the socket is present in the skb, then > > it can be used because that reference is cleaned up while the skb > > is crossing netns. > > > > We want to change that to preserve the socket reference in a future > > patch, so this is a preparation updating netfilter to check if the > > socket netns matches before use it. > > > > Signed-off-by: Flavio Leitner > > Acked-by: Florian Westphal > > Signed-off-by: David S. Miller > > --- > ... > > --- a/net/netfilter/xt_socket.c > > +++ b/net/netfilter/xt_socket.c > > @@ -56,8 +56,12 @@ socket_match(const struct sk_buff *skb, struct xt_action_param *par, > > struct sk_buff *pskb = (struct sk_buff *)skb; > > struct sock *sk = skb->sk; > > > > + if (!net_eq(xt_net(par), sock_net(sk))) > > + sk = NULL; > > + > > I am having trouble with this code. With CONFIG_NET_NS enabled, it crashes > for me in read_pnet() because sk is NULL. > > > if (!sk) > > sk = nf_sk_lookup_slow_v4(xt_net(par), skb, xt_in(par)); > > The old code seems to suggest that sk == NULL was possible. > > I see the problem with the Chrome OS kernel rebased to v4.19-rc5, so I > can not guarantee that this really an upstream problem. The change seems > odd, though. Are you sure that it is not (or, rather, no longer) necessary > to check if sk == NULL before dereferencing it in sock_net() ? Oops, it is necessary but if it's not and the netns doesn't match, we need do the lookup. So, could you check if this fixes the problem for you? >>From a5f927e7f1368d753f87cb978d630d786d5adb62 Mon Sep 17 00:00:00 2001 From: Flavio Leitner Date: Thu, 27 Sep 2018 19:36:28 -0300 Subject: [PATCH] xt_socket: check sk before checking for netns. Only check for the network namespace if the socket is available. Fixes: f564650106a6 ("netfilter: check if the socket netns is correct.") Reported-by: Guenter Roeck Signed-off-by: Flavio Leitner --- net/netfilter/xt_socket.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/netfilter/xt_socket.c b/net/netfilter/xt_socket.c index 0472f3472842..ada144e5645b 100644 --- a/net/netfilter/xt_socket.c +++ b/net/netfilter/xt_socket.c @@ -56,7 +56,7 @@ socket_match(const struct sk_buff *skb, struct xt_action_param *par, struct sk_buff *pskb = (struct sk_buff *)skb; struct sock *sk = skb->sk; - if (!net_eq(xt_net(par), sock_net(sk))) + if (sk && !net_eq(xt_net(par), sock_net(sk))) sk = NULL; if (!sk) @@ -117,7 +117,7 @@ socket_mt6_v1_v2_v3(const struct sk_buff *skb, struct xt_action_param *par) struct sk_buff *pskb = (struct sk_buff *)skb; struct sock *sk = skb->sk; - if (!net_eq(xt_net(par), sock_net(sk))) + if (sk && !net_eq(xt_net(par), sock_net(sk))) sk = NULL; if (!sk) -- 2.14.4