On Sun, May 24, 2020 at 11:00 AM Eric Dumazet <eduma...@google.com> wrote:
>
> Unpriv users can use traceroute over plain UDP sockets, but not TCP ones.
>
> $ traceroute -Mtcp 8.8.8.8
> You do not have enough privileges to use this traceroute method.
>
> $ traceroute -n -Mudp 8.8.8.8
> traceroute to 8.8.8.8 (8.8.8.8), 30 hops max, 60 byte packets
> 1 192.168.86.1 3.631 ms 3.512 ms 3.405 ms
> 2 10.1.10.1 4.183 ms 4.125 ms 4.072 ms
> 3 96.120.88.125 20.621 ms 19.462 ms 20.553 ms
> 4 96.110.177.65 24.271 ms 25.351 ms 25.250 ms
> 5 69.139.199.197 44.492 ms 43.075 ms 44.346 ms
> 6 68.86.143.93 27.969 ms 25.184 ms 25.092 ms
> 7 96.112.146.18 25.323 ms 96.112.146.22 25.583 ms 96.112.146.26 24.502 ms
> 8 72.14.239.204 24.405 ms 74.125.37.224 16.326 ms 17.194 ms
> 9 209.85.251.9 18.154 ms 209.85.247.55 14.449 ms 209.85.251.9 26.296 ms^C
>
> We can easily support traceroute over TCP, by queueing an error message
> into socket error queue.
>
> Note that applications need to set IP_RECVERR/IPV6_RECVERR option to
> enable this feature, and that the error message is only queued
> while in SYN_SNT state.
>
> socket(AF_INET6, SOCK_STREAM, IPPROTO_IP) = 3
> setsockopt(3, SOL_IPV6, IPV6_RECVERR, [1], 4) = 0
> setsockopt(3, SOL_SOCKET, SO_TIMESTAMP_OLD, [1], 4) = 0
> setsockopt(3, SOL_IPV6, IPV6_UNICAST_HOPS, [5], 4) = 0
> connect(3, {sa_family=AF_INET6, sin6_port=htons(8787), sin6_flowinfo=htonl(0),
> inet_pton(AF_INET6, "2002:a05:6608:297::", &sin6_addr),
> sin6_scope_id=0}, 28) = -1 EHOSTUNREACH (No route to host)
> recvmsg(3, {msg_name={sa_family=AF_INET6, sin6_port=htons(8787),
> sin6_flowinfo=htonl(0),
> inet_pton(AF_INET6, "2002:a05:6608:297::", &sin6_addr),
> sin6_scope_id=0},
> msg_namelen=1024->28,
> msg_iov=[{iov_base="`\r\337\320\0004\6\1&\7\370\260\200\231\16\27\0\0\0\0\0\0\0\0
> \2\n\5f\10\2\227"..., iov_len=1024}],
> msg_iovlen=1, msg_control=[{cmsg_len=32, cmsg_level=SOL_SOCKET,
> cmsg_type=SO_TIMESTAMP_OLD, cmsg_data={tv_sec=1590340680, tv_usec=272424}},
> {cmsg_len=60, cmsg_level=SOL_IPV6,
> cmsg_type=IPV6_RECVERR}],
> msg_controllen=96, msg_flags=MSG_ERRQUEUE}, MSG_ERRQUEUE) = 144
>
> Suggested-by: Maciej Żenczykowski <m...@google.com
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Cc: Willem de Bruijn <will...@google.com>
> ---
> net/ipv4/tcp_ipv4.c | 2 ++
> net/ipv6/tcp_ipv6.c | 2 ++
> 2 files changed, 4 insertions(+)
>
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index
> 6c05f1ceb538cbb9981835440163485de2ccf716..900c6d154cbcf04fb09d71f1445d0723bcf3c409
> 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -573,6 +573,8 @@ int tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
> if (fastopen && !fastopen->sk)
> break;
>
> + ip_icmp_error(sk, skb, err, th->dest, info, (u8 *)th);
> +
> if (!sock_owned_by_user(sk)) {
> sk->sk_err = err;
>
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index
> 413b3425ac66bd758bb83562efa955f277da90a5..01a6f5111a77b4397038bf4d40cc09a94e57408c
> 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -463,6 +463,8 @@ static int tcp_v6_err(struct sk_buff *skb, struct
> inet6_skb_parm *opt,
> if (fastopen && !fastopen->sk)
> break;
>
> + ipv6_icmp_error(sk, skb, err, th->dest, ntohl(info), (u8
> *)th);
> +
> if (!sock_owned_by_user(sk)) {
> sk->sk_err = err;
> sk->sk_error_report(sk); /* Wake
> people up to see the error (see connect in sock.c) */
> --
> 2.27.0.rc0.183.gde8f92d652-goog
Thanks! I was not expecting it to be this easy...
Reviewed-by: Maciej Żenczykowski <m...@google.com>
