linux-kernel - Re: [PATCH nf] netfilter: ensure rcu_read_lock() in ipv4_find

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Message-ID: <CAGnkfhzA6j2B43DFgQedeGE6H5XvHKWd7KPg3ocGVr0K_u2NJA@mail.gmail.com>
Date:   Mon, 24 Feb 2020 20:47:13 +0100
From:   Matteo Croce <mcroce@...hat.com>
To:     Florian Westphal <fw@...len.de>
Cc:     netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Stephen Suryaputra <ssuryaextr@...il.com>
Subject: Re: [PATCH nf] netfilter: ensure rcu_read_lock() in ipv4_find_option()

On Mon, Feb 24, 2020 at 8:42 PM Matteo Croce <mcroce@...hat.com> wrote:
>
> On Mon, Feb 24, 2020 at 8:12 PM Florian Westphal <fw@...len.de> wrote:
> >
> > Matteo Croce <mcroce@...hat.com> wrote:
> > > As in commit c543cb4a5f07 ("ipv4: ensure rcu_read_lock() in ipv4_link_failure()")
> > > and commit 3e72dfdf8227 ("ipv4: ensure rcu_read_lock() in cipso_v4_error()"),
> > > __ip_options_compile() must be called under rcu protection.
> >
> > This is not needed, all netfilter hooks run with rcu_read_lock held.
> >
>
> Ok, so let's drop it, thanks.

What about adding a RCU_LOCKDEP_WARN() in __ip_options_compile() to
protect against future errors? Something like:

----------------------------------%<-------------------------------------
@@ -262,6 +262,9 @@ int __ip_options_compile(struct net *net,
  unsigned char *iph;
  int optlen, l;

+ RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
+ __FUNC__ " needs rcu_read_lock() protection");
+
  if (skb) {
  rt = skb_rtable(skb);
  optptr = (unsigned char *)&(ip_hdr(skb)[1]);
---------------------------------->%-------------------------------------

Bye,
-- 
Matteo Croce
per aspera ad upstream