6.6-stable review patch. If anyone has any objections, please let me know.
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From: Ido Schimmel idosch@nvidia.com
[ 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 willemdebruijn.kernel@gmail.com Closes: https://lore.kernel.org/netdev/67efef607bc41_1ddca82948c@willemb.c.googlers.... Signed-off-by: Ido Schimmel idosch@nvidia.com Reviewed-by: Willem de Bruijn willemb@google.com Reviewed-by: David Ahern dsahern@kernel.org Link: https://patch.msgid.link/20250408084316.243559-1-idosch@nvidia.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 2e98531fa51a3..53197087353a7 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -472,10 +472,10 @@ 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; }