From 7a91926c76c05ddfa577b71a086e641adf8b0581 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Mon, 17 Feb 2025 17:02:42 +0100 Subject: [PATCH] netfilter: nft_ct: Use __refcount_inc() for per-CPU nft_ct_pcpu_template. [ Upstream commit 5cfe5612ca9590db69b9be29dc83041dbf001108 ] nft_ct_pcpu_template is a per-CPU variable and relies on disabled BH for its locking. The refcounter is read and if its value is set to one then the refcounter is incremented and variable is used - otherwise it is already in use and left untouched. Without per-CPU locking in local_bh_disable() on PREEMPT_RT the read-then-increment operation is not atomic and therefore racy. This can be avoided by using unconditionally __refcount_inc() which will increment counter and return the old value as an atomic operation. In case the returned counter is not one, the variable is in use and we need to decrement counter. Otherwise we can use it. Use __refcount_inc() instead of read and a conditional increment. Fixes: edee4f1e9245 ("netfilter: nft_ct: add zone id set support") Signed-off-by: Sebastian Andrzej Siewior Reviewed-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso Signed-off-by: Sasha Levin --- net/netfilter/nft_ct.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/net/netfilter/nft_ct.c b/net/netfilter/nft_ct.c index 6157f8b4a3ce..3641043ca8cc 100644 --- a/net/netfilter/nft_ct.c +++ b/net/netfilter/nft_ct.c @@ -240,6 +240,7 @@ static void nft_ct_set_zone_eval(const struct nft_expr *expr, enum ip_conntrack_info ctinfo; u16 value = nft_reg_load16(®s->data[priv->sreg]); struct nf_conn *ct; + int oldcnt; ct = nf_ct_get(skb, &ctinfo); if (ct) /* already tracked */ @@ -260,10 +261,11 @@ static void nft_ct_set_zone_eval(const struct nft_expr *expr, ct = this_cpu_read(nft_ct_pcpu_template); - if (likely(refcount_read(&ct->ct_general.use) == 1)) { - refcount_inc(&ct->ct_general.use); + __refcount_inc(&ct->ct_general.use, &oldcnt); + if (likely(oldcnt == 1)) { nf_ct_zone_add(ct, &zone); } else { + refcount_dec(&ct->ct_general.use); /* previous skb got queued to userspace, allocate temporary * one until percpu template can be reused. */