On Wed, Aug 17, 2022 at 02:30:01PM -0700, Alexei Starovoitov wrote:
> On Wed, Aug 17, 2022 at 11:43 AM Daniel Xu <dxu@xxxxxxxxx> wrote:
> >
> > +/* Check writes into `struct nf_conn` */
> > +int nf_conntrack_btf_struct_access(struct bpf_verifier_log *log,
> > + const struct btf *btf,
> > + const struct btf_type *t, int off,
> > + int size, enum bpf_access_type atype,
> > + u32 *next_btf_id,
> > + enum bpf_type_flag *flag)
> > +{
> > + const struct btf_type *nct = READ_ONCE(nf_conn_type);
> > + s32 type_id;
> > + size_t end;
> > +
> > + if (!nct) {
> > + type_id = btf_find_by_name_kind(btf, "nf_conn", BTF_KIND_STRUCT);
> > + if (type_id < 0)
> > + return -EINVAL;
> > +
> > + nct = btf_type_by_id(btf, type_id);
> > + WRITE_ONCE(nf_conn_type, nct);
> > + }
> > +
> > + if (t != nct) {
> > + bpf_log(log, "only read is supported\n");
> > + return -EACCES;
> > + }
> > +
> > + switch (off) {
> > +#if defined(CONFIG_NF_CONNTRACK_MARK)
> > + case offsetof(struct nf_conn, mark):
> > + end = offsetofend(struct nf_conn, mark);
> > + break;
> > +#endif
> > + default:
> > + bpf_log(log, "no write support to nf_conn at off %d\n", off);
> > + return -EACCES;
> > + }
> > +
> > + if (off + size > end) {
> > + bpf_log(log,
> > + "write access at off %d with size %d beyond the member of nf_conn ended at %zu\n",
> > + off, size, end);
> > + return -EACCES;
> > + }
> > +
> > + return NOT_INIT;
>
> Took me a long time to realize that this is a copy-paste
> from net/ipv4/bpf_tcp_ca.c.
> It's not wrong, but misleading.
> When atype == BPF_READ the return value from
> btf_struct_access should only be error<0, SCALAR_VALUE, PTR_TO_BTF_ID.
> For atype == BPF_WRITE we should probably standardize on
> error<0, or 0.
>
> The NOT_INIT happens to be zero, but explicit 0
> is cleaner to avoid confusion that this is somehow enum bpf_reg_type.
>
> Martin,
> since you've added this code in bpf_tcp_ca, wdyt?
Yep, sgtm. This will be less confusing.
