Re: [PATCH v2 3/5] bpf: add helper masks for ADJ_ROOM flags and encap validation

[Martin KaFai Lau]

On 3/26/26 10:02 AM, Hudson, Nick wrote:
> > >     static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> > >        u64 flags)
> > > @@ -3502,6 +3513,11 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> > >    unsigned int gso_type = SKB_GSO_DODGY;
> > >    int ret;
> > >   + if (unlikely(flags & ~(BPF_F_ADJ_ROOM_ENCAP_MASK |
> > > +        BPF_F_ADJ_ROOM_NO_CSUM_RESET |
> > > +        BPF_F_ADJ_ROOM_FIXED_GSO)))
> > Under which case this new check will be hit?
> If a user supplies +ve len_diff and attempts to pass a DECAP flag.
>
> The commit message had
>
>      Add flag validation to bpf_skb_net_grow() to reject invalid encap
>      flags early.

There is DECAP_MASK check in bpf_skb_adjust_room() and then !shrink is 
rejected. What am I missing?