On Mon, 25 Aug 2025 12:39:14 -0700 Amery Hung wrote:
> +__bpf_kfunc int bpf_xdp_pull_data(struct xdp_md *x, u32 len, u64 flags)
> +{
> + struct xdp_buff *xdp = (struct xdp_buff *)x;
> + struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
> + void *data_end, *data_hard_end = xdp_data_hard_end(xdp);
> + int i, delta, buff_len, n_frags_free = 0, len_free = 0;
> +
> + buff_len = xdp_get_buff_len(xdp);
> +
> + if (unlikely(len > buff_len))
> + return -EINVAL;
> +
> + if (!len)
> + len = xdp_get_buff_len(xdp);
> +
> + data_end = xdp->data + len;
> + delta = data_end - xdp->data_end;
> +
> + if (delta <= 0)
> + return 0;
> +
> + if (unlikely(data_end > data_hard_end))
> + return -EINVAL;
Is this safe against pointers wrapping on 32b systems?
Maybe it's better to do:
if (unlikely(data_hard_end - xdp->data_end < delta))
?
> + for (i = 0; i < sinfo->nr_frags && delta; i++) {
> + skb_frag_t *frag = &sinfo->frags[i];
> + u32 shrink = min_t(u32, delta, skb_frag_size(frag));
> +
> + memcpy(xdp->data_end + len_free, skb_frag_address(frag), shrink);
> +
> + len_free += shrink;
> + delta -= shrink;
> + if (bpf_xdp_shrink_data(xdp, frag, shrink, false))
> + n_frags_free++;
possibly
else
break;
and then you don't have to check delta in the for loop condition?
> + }
> +
> + for (i = 0; i < sinfo->nr_frags - n_frags_free; i++) {
> + memcpy(&sinfo->frags[i], &sinfo->frags[i + n_frags_free],
> + sizeof(skb_frag_t));
This feels like it'd really want to be a memmove(), no?
> + }
> +
> + sinfo->nr_frags -= n_frags_free;
> + sinfo->xdp_frags_size -= len_free;
> + xdp->data_end = data_end;
> +
> + if (unlikely(!sinfo->nr_frags))
> + xdp_buff_clear_frags_flag(xdp);
> +
> + return 0;
> +}
