net/flow_dissector: switch to siphash
authorEric Dumazet <edumazet@google.com>
Tue, 22 Oct 2019 14:57:46 +0000 (07:57 -0700)
committerDavid S. Miller <davem@davemloft.net>
Thu, 24 Oct 2019 03:13:22 +0000 (20:13 -0700)
commit55667441c84fa5e0911a0aac44fb059c15ba6da2
tree83d3fb8a5acbfbb3f9766f30a1e2343f0f19a90b
parent6c5d9c2a6bedbb3c3c14253776320c0ee564f064
net/flow_dissector: switch to siphash

UDP IPv6 packets auto flowlabels are using a 32bit secret
(static u32 hashrnd in net/core/flow_dissector.c) and
apply jhash() over fields known by the receivers.

Attackers can easily infer the 32bit secret and use this information
to identify a device and/or user, since this 32bit secret is only
set at boot time.

Really, using jhash() to generate cookies sent on the wire
is a serious security concern.

Trying to change the rol32(hash, 16) in ip6_make_flowlabel() would be
a dead end. Trying to periodically change the secret (like in sch_sfq.c)
could change paths taken in the network for long lived flows.

Let's switch to siphash, as we did in commit df453700e8d8
("inet: switch IP ID generator to siphash")

Using a cryptographically strong pseudo random function will solve this
privacy issue and more generally remove other weak points in the stack.

Packet schedulers using skb_get_hash_perturb() benefit from this change.

Fixes: b56774163f99 ("ipv6: Enable auto flow labels by default")
Fixes: 42240901f7c4 ("ipv6: Implement different admin modes for automatic flow labels")
Fixes: 67800f9b1f4e ("ipv6: Call skb_get_hash_flowi6 to get skb->hash in ip6_make_flowlabel")
Fixes: cb1ce2ef387b ("ipv6: Implement automatic flow label generation on transmit")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Jonathan Berger <jonathann1@walla.com>
Reported-by: Amit Klein <aksecurity@gmail.com>
Reported-by: Benny Pinkas <benny@pinkas.net>
Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
include/linux/skbuff.h
include/net/flow_dissector.h
include/net/fq.h
include/net/fq_impl.h
net/core/flow_dissector.c
net/sched/sch_hhf.c
net/sched/sch_sfb.c
net/sched/sch_sfq.c