From 07505f0dddd926f898e96e3f1aad710f43430bca Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 26 Oct 2022 18:10:52 +0800 Subject: [PATCH] tcp: add some entropy in __inet_hash_connect() stable inclusion from stable-v5.10.125 commit 743acb520799bd8987edb7d1282b7eeddeb8f986 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6EY Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=743acb520799bd8987edb7d1282b7eeddeb8f986 -------------------------------- commit c579bd1b4021c42ae247108f1e6f73dd3f08600c upstream. Even when implementing RFC 6056 3.3.4 (Algorithm 4: Double-Hash Port Selection Algorithm), a patient attacker could still be able to collect enough state from an otherwise idle host. Idea of this patch is to inject some noise, in the cases __inet_hash_connect() found a candidate in the first attempt. This noise should not significantly reduce the collision avoidance, and should be zero if connection table is already well used. Note that this is not implementing RFC 6056 3.3.5 because we think Algorithm 5 could hurt typical workloads. Signed-off-by: Eric Dumazet Cc: David Dworken Cc: Willem de Bruijn Signed-off-by: David S. Miller Cc: Ben Hutchings Signed-off-by: Greg Kroah-Hartman Signed-off-by: Zheng Zengkai Reviewed-by: Wei Li --- net/ipv4/inet_hashtables.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index 2bb9ded807ee..aadafcf7358b 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -833,6 +833,11 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row, return -EADDRNOTAVAIL; ok: + /* If our first attempt found a candidate, skip next candidate + * in 1/16 of cases to add some noise. + */ + if (!i && !(prandom_u32() % 16)) + i = 2; WRITE_ONCE(table_perturb[index], READ_ONCE(table_perturb[index]) + i + 2); /* Head lock still held and bh's disabled */ -- GitLab