netdev - Re: [PATCH net] net/flow_dissector: switch to siphash

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Date:   Wed, 23 Oct 2019 20:13:49 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        jonathann1@...la.com, aksecurity@...il.com, benny@...kas.net,
        tom@...bertland.com
Subject: Re: [PATCH net] net/flow_dissector: switch to siphash

From: Eric Dumazet <edumazet@...gle.com>
Date: Tue, 22 Oct 2019 07:57:46 -0700

> 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@...gle.com>
> Reported-by: Jonathan Berger <jonathann1@...la.com>
> Reported-by: Amit Klein <aksecurity@...il.com>
> Reported-by: Benny Pinkas <benny@...kas.net>

Applied and queued up for -stable, thanks Eric.