Re: [PATCH bpf-next 1/2] bpf: add bpf_init_inode_xattr kfunc for atomic inode labeling

[David Windsor]

Hi,

> >
> > > Even if we wanted to ensure argument provenance was stuff loaded from
> > > context, the right solution would be some kfunc flag that constraints
> > > the argument to be derived by following the ctx pointer, not whatever
> > > is done in this patch.
> >
> > OK, so it is provenance-like tracking which you were initially kinda
> > alluding to here. Currently, I don't believe that PTR_TO_CTX is
> > preserved upon any subsequent R1 (ctx) dereferences, so we'd need to
> > think about how this type could be preserved such that we can enforce
> > this kinda constraint (__ctx) at the time which the new BPF kfunc is
> > called. Do you have any ideas on how to do this?
>
> I think we'll have to track in the register whether the PTR_TO_BTF_ID
> came from a PTR_TO_CTX load. That said, I still prefer changing the
> prototype to pack the array and its output size parameter together. It
> is even clearer to have a well named type than int *xattr_count in the
> prototype.

Thanks for your feedback, sorry I've been busy this week. I will send
v2 with this change, as well as Matt's suggested change for guarding
the bpf xattr namespace.