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@gondor.apana.org.au>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index cc9bcf008b0337a7082eefe6f6278cf5d59a6804..ef5f77b44ec72131e45b86456c83be7462da224e 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -3129,7 +3129,7 @@ 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,