[PATCH 5.15 136/215] netfilter: nft_counter: Disable BH in nft_counter_offload_stats().

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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

[ Upstream commit 1eacdd71b3436b54d5fc8218c4bb0187d92a6892 ]

The sequence counter nft_counter_seq is a per-CPU counter. There is no
lock associated with it. nft_counter_do_eval() is using the same counter
and disables BH which suggest that it can be invoked from a softirq.
This in turn means that nft_counter_offload_stats(), which disables only
preemption, can be interrupted by nft_counter_do_eval() leading to two
writer for one seqcount_t.
This can lead to loosing stats or reading statistics while they are
updated.

Disable BH during stats update in nft_counter_offload_stats() to ensure
one writer at a time.

Fixes: b72920f6e4a9d ("netfilter: nftables: counter hardware offload support")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Reviewed-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/netfilter/nft_counter.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nft_counter.c b/net/netfilter/nft_counter.c
index 1b468a16b5237..f10d36c693b13 100644
--- a/net/netfilter/nft_counter.c
+++ b/net/netfilter/nft_counter.c
@@ -264,7 +264,7 @@ static void nft_counter_offload_stats(struct nft_expr *expr,
 	struct nft_counter *this_cpu;
 	seqcount_t *myseq;
 
-	preempt_disable();
+	local_bh_disable();
 	this_cpu = this_cpu_ptr(priv->counter);
 	myseq = this_cpu_ptr(&nft_counter_seq);
 
@@ -272,7 +272,7 @@ static void nft_counter_offload_stats(struct nft_expr *expr,
 	this_cpu->packets += stats->pkts;
 	this_cpu->bytes += stats->bytes;
 	write_seqcount_end(myseq);
-	preempt_enable();
+	local_bh_enable();
 }
 
 static struct nft_expr_type nft_counter_type;
-- 
2.43.0







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