[PATCH 3.16 112/136] inet: stop leaking jiffies on the wire

Ben Hutchings
2019-12-17T00:54:07Z

From: Eric Dumazet <edumazet@google.com>

commit a904a0693c189691eeee64f6c6b188bd7dc244e9 upstream.

Historically linux tried to stick to RFC 791, 1122, 2003
for IPv4 ID field generation.

RFC 6864 made clear that no matter how hard we try,
we can not ensure unicity of IP ID within maximum
lifetime for all datagrams with a given source
address/destination address/protocol tuple.

Linux uses a per socket inet generator (inet_id), initialized
at connection startup with a XOR of 'jiffies' and other
fields that appear clear on the wire.

Thiemo Nagel pointed that this strategy is a privacy
concern as this provides 16 bits of entropy to fingerprint
devices.

Let's switch to a random starting point, this is just as
good as far as RFC 6864 is concerned and does not leak
anything critical.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Thiemo Nagel <tnagel@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: drop changes in chelsio]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -122,7 +122,7 @@ int dccp_v4_connect(struct sock *sk, str
inet->inet_daddr,
inet->inet_sport,
inet->inet_dport);
- inet->inet_id = dp->dccps_iss ^ jiffies;
+ inet->inet_id = prandom_u32();

err = dccp_connect(sk);
rt = NULL;
--- a/net/ipv4/datagram.c
+++ b/net/ipv4/datagram.c
@@ -74,7 +74,7 @@ int __ip4_datagram_connect(struct sock *
inet->inet_daddr = fl4->daddr;
inet->inet_dport = usin->sin_port;
sk->sk_state = TCP_ESTABLISHED;
- inet->inet_id = jiffies;
+ inet->inet_id = prandom_u32();

sk_dst_set(sk, &rt->dst);
err = 0;
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -241,7 +241,7 @@ int tcp_v4_connect(struct sock *sk, stru
inet->inet_sport,
usin->sin_port);

- inet->inet_id = tp->write_seq ^ jiffies;
+ inet->inet_id = prandom_u32();

err = tcp_connect(sk);

@@ -1449,7 +1449,7 @@ struct sock *tcp_v4_syn_recv_sock(struct
inet_csk(newsk)->icsk_ext_hdr_len = 0;
if (inet_opt)
inet_csk(newsk)->icsk_ext_hdr_len = inet_opt->opt.optlen;
- newinet->inet_id = newtp->write_seq ^ jiffies;
+ newinet->inet_id = prandom_u32();

if (!dst) {
dst = inet_csk_route_child_sock(sk, newsk, req);
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -7006,7 +7006,7 @@ void sctp_copy_sock(struct sock *newsk,
newinet->inet_rcv_saddr = inet->inet_rcv_saddr;
newinet->inet_dport = htons(asoc->peer.port);
newinet->pmtudisc = inet->pmtudisc;
- newinet->inet_id = asoc->next_tsn ^ jiffies;
+ newinet->inet_id = prandom_u32();

newinet->uc_ttl = inet->uc_ttl;
newinet->mc_loop = 1;