Re: [PATCH bpf] xdp: use trusted arguments in XDP hints kfuncs

[Stanislav Fomichev]

On Tue, Jul 11, 2023 at 7:21 AM Jesper Dangaard Brouer
<jbrouer@xxxxxxxxxx> wrote:
>
>
> On 11/07/2023 12.59, Larysa Zaremba wrote:
> > Currently, verifier does not reject XDP programs that pass NULL pointer to
> > hints functions. At the same time, this case is not handled in any driver
> > implementation (including veth). For example, changing
> >
> > bpf_xdp_metadata_rx_timestamp(ctx, &timestamp);
> >
> > to
> >
> > bpf_xdp_metadata_rx_timestamp(ctx, NULL);
> >
> > in xdp_metadata test successfully crashes the system.
> >
> > Add KF_TRUSTED_ARGS flag to hints kfunc definitions, so driver code
> > does not have to worry about getting invalid pointers.
> >
>
> Looks good to me, assuming this means verifier will reject BPF-prog's
> supplying NULL.
>
> Acked-by: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
>
> > Fixes: 3d76a4d3d4e5 ("bpf: XDP metadata RX kfuncs")
> > Reported-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> > Closes: https://lore.kernel.org/bpf/ZKWo0BbpLfkZHbyE@xxxxxxxxxx/
> > Signed-off-by: Larysa Zaremba <larysa.zaremba@xxxxxxxxx>

Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxx>

Thank you for the fix!

> > ---
> >   net/core/xdp.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/core/xdp.c b/net/core/xdp.c
> > index 41e5ca8643ec..8362130bf085 100644
> > --- a/net/core/xdp.c
> > +++ b/net/core/xdp.c
> > @@ -741,7 +741,7 @@ __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash,
> >   __diag_pop();
> >
> >   BTF_SET8_START(xdp_metadata_kfunc_ids)
> > -#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, 0)
> > +#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, KF_TRUSTED_ARGS)
> >   XDP_METADATA_KFUNC_xxx
> >   #undef XDP_METADATA_KFUNC
> >   BTF_SET8_END(xdp_metadata_kfunc_ids)
>