Re: [PATCH] net: sched: fix possible OOB write in fl_set_geneve_opt()

[Hangyu Hua]

On 30/5/2023 22:29, Pieter Jansen van Vuuren wrote:
> On 30/05/2023 12:36, Simon Horman wrote:
> > [Updated Pieter's email address, dropped old email address of mine]
>
> Thank you Simon.
>
> > On Mon, May 29, 2023 at 12:36:15PM +0800, Hangyu Hua wrote:
> > > If we send two TCA_FLOWER_KEY_ENC_OPTS_GENEVE packets and their total
> > > size is 252 bytes(key->enc_opts.len = 252) then
> > > key->enc_opts.len = opt->length = data_len / 4 = 0 when the third
> > > TCA_FLOWER_KEY_ENC_OPTS_GENEVE packet enters fl_set_geneve_opt. This
> > > bypasses the next bounds check and results in an out-of-bounds.
> > >
> > > Fixes: 0a6e77784f49 ("net/sched: allow flower to match tunnel options")
> > > Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx>
> >
> > Hi Hangyu Hua,
> >
> > Thanks. I think I see the problem too.
> > But I do wonder, is this more general than Geneve options?
> > That is, can this occur with any sequence of options, that
> > consume space in enc_opts (configured in fl_set_key()) that
> > in total are more than 256 bytes?
>
> Hi Hangyu Hua,
>
> Thank you for the patch. In addition to Simon's comment; I think the subject
> headline should include net, i.e. [PATCH net]. Also could you please provide

My bad. I forgot this rule. It seems this won't be included in the final 
patch. Do i need to send a v2?

> an example tc filter add dev... command to replicate the issue? (Just to make
> it a bit easier to understand).

I use poc.c instead of commands to trigger this bug. If you want poc You
can check if there is an email named "Re: A possible LPE vulnerability 
in fl_set_geneve_opt" in your e-mail. I should have sent it to you and 
Simon while replying to security@xxxxxxxxxx.

Thanks,
Hangyu

> > > ---
> > >   net/sched/cls_flower.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > >
> > > diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
> > > index e960a46b0520..a326fbfe4339 100644
> > > --- a/net/sched/cls_flower.c
> > > +++ b/net/sched/cls_flower.c
> > > @@ -1153,6 +1153,9 @@ static int fl_set_geneve_opt(const struct nlattr *nla, struct fl_flow_key *key,
> > >   	if (option_len > sizeof(struct geneve_opt))
> > >   		data_len = option_len - sizeof(struct geneve_opt);
> > >   
> > > +	if (key->enc_opts.len > FLOW_DIS_TUN_OPTS_MAX - 4)
> > > +		return -ERANGE;
> > > +
> > >   	opt = (struct geneve_opt *)&key->enc_opts.data[key->enc_opts.len];
> > >   	memset(opt, 0xff, option_len);
> > >   	opt->length = data_len / 4;
> > > --
> > > 2.34.1