5.10-stable review patch. If anyone has any objections, please let me know.
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From: Sebastian Andrzej Siewior bigeasy@linutronix.de
[ 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 bigeasy@linutronix.de Reviewed-by: Florian Westphal fw@strlen.de Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 4b75c7113de4d..f95f1dbc48dea 100644 --- a/net/netfilter/nft_ct.c +++ b/net/netfilter/nft_ct.c @@ -239,6 +239,7 @@ 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 */ @@ -259,10 +260,11 @@ 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. */