netdev - Re: [Patch nf 1/3] xt_hashlimit: avoid OOM for user-controlled vmalloc

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Date:   Fri, 31 Jan 2020 15:17:23 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        NetFilter <netfilter-devel@...r.kernel.org>,
        syzbot <syzbot+adf6c6c2be1c3a718121@...kaller.appspotmail.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>
Subject: Re: [Patch nf 1/3] xt_hashlimit: avoid OOM for user-controlled vmalloc

On Fri, Jan 31, 2020 at 2:08 PM Florian Westphal <fw@...len.de> wrote:
>
> Cong Wang <xiyou.wangcong@...il.com> wrote:
> > The hashtable size could be controlled by user, so use flags
> > GFP_USER | __GFP_NOWARN to avoid OOM warning triggered by user-space.
> >
> > Also add __GFP_NORETRY to avoid retrying, as this is just a
> > best effort and the failure is already handled gracefully.
> >
> > Reported-and-tested-by: syzbot+adf6c6c2be1c3a718121@...kaller.appspotmail.com
> > Cc: Pablo Neira Ayuso <pablo@...filter.org>
> > Cc: Jozsef Kadlecsik <kadlec@...filter.org>
> > Cc: Florian Westphal <fw@...len.de>
> > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> > ---
> >  net/netfilter/xt_hashlimit.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
> > index bccd47cd7190..885a266d8e57 100644
> > --- a/net/netfilter/xt_hashlimit.c
> > +++ b/net/netfilter/xt_hashlimit.c
> > @@ -293,8 +293,9 @@ static int htable_create(struct net *net, struct hashlimit_cfg3 *cfg,
> >               if (size < 16)
> >                       size = 16;
> >       }
> > -     /* FIXME: don't use vmalloc() here or anywhere else -HW */
> > -     hinfo = vmalloc(struct_size(hinfo, hash, size));
> > +     /* FIXME: don't use __vmalloc() here or anywhere else -HW */
> > +     hinfo = __vmalloc(struct_size(hinfo, hash, size),
> > +                       GFP_USER | __GFP_NOWARN | __GFP_NORETRY, PAGE_KERNEL);
>
> Rationale looks sane, wonder if it makes sense to drop Haralds comment
> though, I don't see what other solution other than vmalloc could be used
> here.

I will remove it.

Thanks.