netdev - Re: [PATCH v3 1/2] Make loop indexes unsigned

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Date: Fri, 29 Sep 2023 10:05:59 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: Joao Moreira <joao@...rdrivepizza.com>
Cc: netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kadlec@...filter.org, fw@...len.de, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	rkannoth@...vell.com, wojciech.drewek@...el.com,
	steen.hegenlund@...rohip.com, keescook@...omium.org,
	Joao Moreira <joao.moreira@...el.com>
Subject: Re: [PATCH v3 1/2] Make loop indexes unsigned

On Thu, Sep 28, 2023 at 07:53:14PM -0700, Joao Moreira wrote:
> On 2023-09-28 06:40, Pablo Neira Ayuso wrote:
> > On Wed, Sep 27, 2023 at 09:47:14AM -0700, joao@...rdrivepizza.com wrote:
> > > From: Joao Moreira <joao.moreira@...el.com>
> > > 
> > > Both flow_rule_alloc and offload_action_alloc functions received an
> > > unsigned num_actions parameters which are then operated within a loop.
> > > The index of this loop is declared as a signed int. If it was possible
> > > to pass a large enough num_actions to these functions, it would lead
> > > to
> > > an out of bounds write.
> > > 
> > > After checking with maintainers, it was mentioned that front-end will
> > > cap the num_actions value and that it is not possible to reach this
> > > function with such a large number. Yet, for correctness, it is still
> > > better to fix this.
> > > 
> > > This issue was observed by the commit author while reviewing a
> > > write-up
> > > regarding a CVE within the same subsystem [1].
> > > 
> > > 1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/
> > > 
> > > Signed-off-by: Joao Moreira <joao.moreira@...el.com>
> > > ---
> > >  net/core/flow_offload.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/net/core/flow_offload.c b/net/core/flow_offload.c
> > > index bc5169482710..bc3f53a09d8f 100644
> > > --- a/net/core/flow_offload.c
> > > +++ b/net/core/flow_offload.c
> > > @@ -10,7 +10,7 @@
> > >  struct flow_rule *flow_rule_alloc(unsigned int num_actions)
> > >  {
> > >  	struct flow_rule *rule;
> > > -	int i;
> > > +	unsigned int i;
> > 
> > With the 2^8 cap, I don't think this patch is required anymore.
> 
> Hm. While I understand that there is not a significant menace haunting
> this... would it be good for (1) type correctness and (2) prevent that
> things blow up if something changes and someone misses this spot?

Nothing is going to change, please remove unnecesary updates. Capping
to 2^8 for all hardware offload subsystems is sufficient by now. If
someone needs more than that, it will have to justify it.