On Tue, Oct 6, 2015 at 10:56 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote: > On Tue, 2015-10-06 at 10:50 -0700, Alexei Starovoitov wrote: > >> was also thinking that we can do it only in paths that actually >> have multiple protocol layers, since today bpf is mainly used with >> tcpdump(raw_socket) and new af_packet fanout both have cb cleared >> on RX, because it just came out of alloc_skb and no layers were called, >> and on TX we can clear 20 bytes in dev_queue_xmit_nit(). >> af_unix/netlink also have clean skb. Need to analyze tun and sctp... >> but it feels overly fragile to save a branch in sk_filter, >> so planning to go with >> if(unlikely(prog->cb_access)) memset in sk_filter(). >> > > This will break TCP use of sk_filter(). > skb->cb[] contains useful data in TCP layer. > > Since I don't know too much about the networking details: 1. Does "skb->cb" *ever* contain anything useful for an unprivileged user? 2. Does sbk->cb form a stable ABI? Unless both answers are solid yesses, then maybe the right solution is to just deny access entirely to unprivileged users. --Andy -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
