Máté Eckl <ecklm94@xxxxxxxxx> wrote: > > This looks like its subtly broken, inherited from xt_TPROXY. > > Above skb_header_pointer uses sizeof(udphdr) only, but nf_tproxy_get_sock_v4 > > assumes it gets tcphdr (it checks th->doff, and that might be garbage). > > I thought about why iptables uses udphdr consequently and I think it does > because we do not nead other than source and destination address and port which > is part of the udp header too at the same position. It does for LISTEN case, see __tcp_hdrlen() usage in nf_tproxy_get_sock_v4. > I think they paid attention to this. nf_tproxy_get_sock_v4 treats that pointer > as a tcphdr indeed, but it only uses tcp-related attributes and functions if ip > protocol is IPPROTO_TCP, so what you described does not happen with an udp > packet. It doesn't happen with an udp packet. But in case tcp header wasn't in linar area (skb->data), but in pagefrags (or split), it will be copied by skb_header_pointer to __udphdr (on stack), so in that case we then get out-of-bounds read access. Hence my suggestion to remove 'hp' arg and repeat skb_header_pointer() call with struct tcphdr. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
