netdev - [PATCH net] netlink: use jhash as hashfn for rhashtable

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Message-Id: <1418056230-8700-1-git-send-email-dborkman@redhat.com>
Date:	Mon,  8 Dec 2014 17:30:30 +0100
From:	Daniel Borkmann <dborkman@...hat.com>
To:	davem@...emloft.net
Cc:	netdev@...r.kernel.org, Herbert Xu <herbert@...dor.apana.org.au>,
	Thomas Graf <tgraf@...g.ch>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: [PATCH net] netlink: use jhash as hashfn for rhashtable

For netlink, we shouldn't be using arch_fast_hash() as a hashing
discipline, but rather jhash() instead.

Since netlink sockets can be opened by any user, a local attacker
would be able to easily create collisions with the DPDK-derived
arch_fast_hash(), which trades off performance for security by
using crc32 CPU instructions on x86_64.

While it might have a legimite use case in other places, it should
be avoided in netlink context, though. As rhashtable's API is very
flexible, we could later on still decide on other hashing disciplines,
if legitimate.

Reference: http://thread.gmane.org/gmane.linux.kernel/1844123
Fixes: e341694e3eb5 ("netlink: Convert netlink_lookup() to use RCU protected hash table")
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Thomas Graf <tgraf@...g.ch>
Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
---
 net/netlink/af_netlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0007b81..b6bf8e8 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -3130,7 +3130,7 @@ static int __init netlink_proto_init(void)
 		.head_offset = offsetof(struct netlink_sock, node),
 		.key_offset = offsetof(struct netlink_sock, portid),
 		.key_len = sizeof(u32), /* portid */
-		.hashfn = arch_fast_hash,
+		.hashfn = jhash,
 		.max_shift = 16, /* 64K */
 		.grow_decision = rht_grow_above_75,
 		.shrink_decision = rht_shrink_below_30,
-- 
1.7.11.7

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