Re: [PATCH nf] netfilter: ipset: fix refcount race between list:set GC and swap
From: Jozsef Kadlecsik <hidden>
Date: 2026-07-23 07:33:03
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lkml, netfilter-devel
On Wed, 22 Jul 2026, Xiang Mei (Microsoft) wrote:
__ip_set_put_byindex() resolved the index to a set pointer under RCU,
then took ip_set_ref_lock in __ip_set_put() to decrement set->ref.
ip_set_swap() holds that same lock while swapping both the ip_set_list
slots and the two sets' ref counters, so it can interleave between the
dereference and the lock acquisition, leaving the caller to decrement a
set whose reference already moved to the other index and hit
BUG_ON(set->ref == 0). list_set_gc() reaches this from timer softirq,
which the nfnl mutex does not serialize against swap: an expiring
list:set member calls list_set_del() -> ip_set_put_byindex() while
IPSET_CMD_SWAP runs on the referenced sets.
Resolve the index and decrement under ip_set_ref_lock, as ip_set_swap()
already does, keeping the refcount tied to the index rather than to a
stale set pointer.
kernel BUG at net/netfilter/ipset/ip_set_core.c:685!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
RIP: 0010:ip_set_put_byindex (net/netfilter/ipset/ip_set_core.c:870)
Call Trace:
<IRQ>
list_set_del (net/netfilter/ipset/ip_set_list_set.c:159)
set_cleanup_entries (net/netfilter/ipset/ip_set_list_set.c:181)
list_set_gc (net/netfilter/ipset/ip_set_list_set.c:578)
call_timer_fn (kernel/time/timer.c:1748)
__run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2374)
run_timer_softirq (kernel/time/timer.c:2405)
</IRQ>
Kernel panic - not syncing: Fatal exception in interrupt
Fixes: 9076aea76538 ("netfilter: ipset: Increase the number of maximal sets automatically")
Reported-by: AutonomousCodeSecurity@microsoft.com
Signed-off-by: Xiang Mei (Microsoft) <redacted>Acked-by: Jozsef Kadlecsik <redacted> Best regards, Jozsef
quoted hunk ↗ jump to hunk
--- net/netfilter/ipset/ip_set_core.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-)diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c index 6cfad152d7d1..16d33c3e28cf 100644 --- a/net/netfilter/ipset/ip_set_core.c +++ b/net/netfilter/ipset/ip_set_core.c@@ -679,11 +679,18 @@ __ip_set_get(struct ip_set *set)} static void -__ip_set_put(struct ip_set *set) +__ip_set_put_locked(struct ip_set *set) { - write_lock_bh(&ip_set_ref_lock); + lockdep_assert_held(&ip_set_ref_lock); BUG_ON(set->ref == 0); set->ref--; +} + +static void +__ip_set_put(struct ip_set *set) +{ + write_lock_bh(&ip_set_ref_lock); + __ip_set_put_locked(set); write_unlock_bh(&ip_set_ref_lock); }@@ -854,11 +861,11 @@ __ip_set_put_byindex(struct ip_set_net *inst, ip_set_id_t index){ struct ip_set *set; - rcu_read_lock(); - set = rcu_dereference(inst->ip_set_list)[index]; + write_lock_bh(&ip_set_ref_lock); + set = ip_set(inst, index); if (set) - __ip_set_put(set); - rcu_read_unlock(); + __ip_set_put_locked(set); + write_unlock_bh(&ip_set_ref_lock); } void -- 2.43.0