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?
