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

[Joao Moreira]

On 2023-09-28 06:40, Pablo Neira Ayuso wrote:
> On Wed, Sep 27, 2023 at 09:47:14AM -0700, joao@xxxxxxxxxxxxxxxxxx 
> wrote:
> > From: Joao Moreira <joao.moreira@xxxxxxxxx>
> >
> > 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@xxxxxxxxx>
> > ---
> >  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?

> >  	rule = kzalloc(struct_size(rule, action.entries, num_actions),
> >  		       GFP_KERNEL);
> > @@ -31,7 +31,7 @@ EXPORT_SYMBOL(flow_rule_alloc);
> >  struct flow_offload_action *offload_action_alloc(unsigned int 
> > num_actions)
> >  {
> >  	struct flow_offload_action *fl_action;
> > -	int i;
> > +	unsigned int i;
> >
> >  	fl_action = kzalloc(struct_size(fl_action, action.entries, 
> > num_actions),
> >  			    GFP_KERNEL);
> > --
> > 2.42.0