linux-kernel - Re: [PATCH nf v2] netfilter/osf: avoid OOB read

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Message-ID: <CAAq0SU=nesniZCLBa7xoqJ853sk2_+LaBhenVSZeYoe=82Syow@mail.gmail.com>
Date:   Thu, 31 Aug 2023 11:45:23 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Fernando Fernandez Mancera <ffmancera@...eup.net>,
        "open list:NETFILTER" <netfilter-devel@...r.kernel.org>,
        "open list:NETFILTER" <coreteam@...filter.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>, stable@...nel.org
Subject: Re: [PATCH nf v2] netfilter/osf: avoid OOB read

On Thu, Aug 31, 2023 at 10:37 AM Florian Westphal <fw@...len.de> wrote:
>
> Wander Lairson Costa <wander@...hat.com> wrote:
> >
> > diff --git a/net/netfilter/nfnetlink_osf.c b/net/netfilter/nfnetlink_osf.c
> > index 8f1bfa6ccc2d..13fedf2aaa0f 100644
> > --- a/net/netfilter/nfnetlink_osf.c
> > +++ b/net/netfilter/nfnetlink_osf.c
> > @@ -315,6 +315,9 @@ static int nfnl_osf_add_callback(struct sk_buff *skb,
> >
> >       f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
> >
> > +     if (f->opt_num > ARRAY_SIZE(f->opt))
> > +             return -EINVAL;
> > +
>
> Hmm, this isn't enough; as far as I can see there is no validation
> whatsoever.
>

I didn't get it. It guarantees there is no OOB read of the opt array.

> This should also check that all of:
>
>  char    genre[MAXGENRELEN];
>  char    version[MAXGENRELEN];
>  char    subtype[MAXGENRELEN];
>
> ... have a NUL byte. You could use strnlen() == ARRAY_SIZE() -> EINVAL
> for those.
>

I think the correct way would be memchr(genre/version/subtype, 0, MAXGENRELEN).

> Maybe there is more to be validated. I did not followup with all the
> nested structures buried in user_finger struct.
>

I focused on the reported issue mainly because I am unfamiliar with
the Netfilter layer. Let me take a deeper look.