From a98d0ba2f66570a95dea534ca085a2559efa6ac5 Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Tue, 8 Apr 2025 11:43:16 +0300 Subject: [PATCH] ipv6: Align behavior across nexthops during path selection [ Upstream commit 6933cd4714861eea6848f18396a119d741f25fc3 ] A nexthop is only chosen when the calculated multipath hash falls in the nexthop's hash region (i.e., the hash is smaller than the nexthop's hash threshold) and when the nexthop is assigned a non-negative score by rt6_score_route(). Commit 4d0ab3a6885e ("ipv6: Start path selection from the first nexthop") introduced an unintentional difference between the first nexthop and the rest when the score is negative. When the first nexthop matches, but has a negative score, the code will currently evaluate subsequent nexthops until one is found with a non-negative score. On the other hand, when a different nexthop matches, but has a negative score, the code will fallback to the nexthop with which the selection started ('match'). Align the behavior across all nexthops and fallback to 'match' when the first nexthop matches, but has a negative score. Fixes: 3d709f69a3e7 ("ipv6: Use hash-threshold instead of modulo-N") Fixes: 4d0ab3a6885e ("ipv6: Start path selection from the first nexthop") Reported-by: Willem de Bruijn Closes: https://lore.kernel.org/netdev/67efef607bc41_1ddca82948c@willemb.c.googlers.com.notmuch/ Signed-off-by: Ido Schimmel Reviewed-by: Willem de Bruijn Reviewed-by: David Ahern Link: https://patch.msgid.link/20250408084316.243559-1-idosch@nvidia.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv6/route.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/ipv6/route.c b/net/ipv6/route.c index d6de164720a05..4e6b833dc40bb 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -474,10 +474,10 @@ void fib6_select_path(const struct net *net, struct fib6_result *res, goto out; hash = fl6->mp_hash; - if (hash <= atomic_read(&first->fib6_nh->fib_nh_upper_bound) && - rt6_score_route(first->fib6_nh, first->fib6_flags, oif, - strict) >= 0) { - match = first; + if (hash <= atomic_read(&first->fib6_nh->fib_nh_upper_bound)) { + if (rt6_score_route(first->fib6_nh, first->fib6_flags, oif, + strict) >= 0) + match = first; goto out; } -- 2.47.3