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>
---
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 291ed2026367e..16f40b503d379 100644
--- a/net/netfilter/nft_counter.c
+++ b/net/netfilter/nft_counter.c
@@ -265,7 +265,7 @@ 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);
@@ -273,7 +273,7 @@ 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();
}
void nft_counter_init_seqcount(void)
--
2.45.2
