netfilter: ipset: fix region locking in hash types

JIRA: https://issues.redhat.com/browse/RHEL-115637

commit 8478a72
Author: Jozsef Kadlecsik <kadlec@netfilter.org>
Date:   Wed May 7 17:01:59 2025 +0200

    netfilter: ipset: fix region locking in hash types

    Region locking introduced in v5.6-rc4 contained three macros to handle
    the region locks: ahash_bucket_start(), ahash_bucket_end() which gave
    back the start and end hash bucket values belonging to a given region
    lock and ahash_region() which should give back the region lock belonging
    to a given hash bucket. The latter was incorrect which can lead to a
    race condition between the garbage collector and adding new elements
    when a hash type of set is defined with timeouts.

    Fixes: f66ee04 ("netfilter: ipset: Fix "INFO: rcu detected stall in hash_xxx" reports")
    Reported-by: Kota Toda <kota.toda@gmo-cybersecurity.com>
    Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>
    Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

net/netfilter/ipset/ip_set_hash_gen.h

@@ -63,7 +63,7 @@ struct hbucket {
 #define ahash_sizeof_regions(htable_bits)		\
 	(ahash_numof_locks(htable_bits) * sizeof(struct ip_set_region))
 #define ahash_region(n, htable_bits)		\
-	((n) % ahash_numof_locks(htable_bits))
+	((n) / jhash_size(HTABLE_REGION_BITS))
 #define ahash_bucket_start(h,  htable_bits)	\
 	((htable_bits) < HTABLE_REGION_BITS ? 0	\
 		: (h) * jhash_size(HTABLE_REGION_BITS))