Re: [PATCH bpf-next v4 2/6] netfilter: bpf: Support BPF_F_NETFILTER_IP_DEFRAG in netfilter link

[Daniel Xu]

Hi Alexei,

On Wed, Jul 12, 2023 at 05:43:49PM -0700, Alexei Starovoitov wrote:
> On Wed, Jul 12, 2023 at 4:44 PM Daniel Xu <dxu@xxxxxxxxx> wrote:
> > +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
> > +       case NFPROTO_IPV6:
> > +               rcu_read_lock();
> > +               v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > +               if (!v6_hook) {
> > +                       rcu_read_unlock();
> > +                       err = request_module("nf_defrag_ipv6");
> > +                       if (err)
> > +                               return err < 0 ? err : -EINVAL;
> > +
> > +                       rcu_read_lock();
> > +                       v6_hook = rcu_dereference(nf_defrag_v6_hook);
> > +                       if (!v6_hook) {
> > +                               WARN_ONCE(1, "nf_defrag_ipv6_hooks bad registration");
> > +                               err = -ENOENT;
> > +                               goto out_v6;
> > +                       }
> > +               }
> > +
> > +               err = v6_hook->enable(link->net);
> 
> I was about to apply, but luckily caught this issue in my local test:
> 
> [   18.462448] BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:283
> [   18.463238] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid:
> 2042, name: test_progs
> [   18.463927] preempt_count: 0, expected: 0
> [   18.464249] RCU nest depth: 1, expected: 0
> [   18.464631] CPU: 15 PID: 2042 Comm: test_progs Tainted: G
> O       6.4.0-04319-g6f6ec4fa00dc #4896
> [   18.465480] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
> [   18.466531] Call Trace:
> [   18.466767]  <TASK>
> [   18.466975]  dump_stack_lvl+0x32/0x40
> [   18.467325]  __might_resched+0x129/0x180
> [   18.467691]  mutex_lock+0x1a/0x40
> [   18.468057]  nf_defrag_ipv4_enable+0x16/0x70
> [   18.468467]  bpf_nf_link_attach+0x141/0x300
> [   18.468856]  __sys_bpf+0x133e/0x26d0
> 
> You cannot call mutex under rcu_read_lock.

Whoops, my bad. I think this patch should fix it:

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