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Date:   Sun, 24 May 2020 11:00:02 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "Maciej ┼╗enczykowski" <maze@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net-next] tcp: allow traceroute -Mtcp for unpriv users

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 ┼╗enczykowski <maze@...gle.com
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Willem de Bruijn <willemb@...gle.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

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