* Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > 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. So this kind of instrumentation data is not an ABI in a similar fashion as tracing information is not an ABI either. I.e. tracepoints can (and sometimes do) change 'semantics' - in that the interpretation of the implementational details behind that data changes as the implementation changes. That's not something that can ever be an ABI, just like the contents of /proc/kcore or /proc/slabinfo can not be an ABI. Thanks, Ingo -- 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
