[PATCH net 03/10] netfilter: nft_quota: use atomic64_xchg for reset

[Florian Westphal <fw@strlen.de>]

From: Brian Witte <brianwitte@mailfence.com>

Use atomic64_xchg() to atomically read and zero the consumed value
on reset, which is simpler than the previous read+sub pattern and
doesn't require lock serialization.

Fixes: bd662c4218f9 ("netfilter: nf_tables: Add locking for NFT_MSG_GETOBJ_RESET requests")
Fixes: 3d483faa6663 ("netfilter: nf_tables: Add locking for NFT_MSG_GETSETELEM_RESET requests")
Fixes: 3cb03edb4de3 ("netfilter: nf_tables: Add locking for NFT_MSG_GETRULE_RESET requests")
Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Brian Witte <brianwitte@mailfence.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nft_quota.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nft_quota.c b/net/netfilter/nft_quota.c
index df0798da2329..cb6c0e04ff67 100644
--- a/net/netfilter/nft_quota.c
+++ b/net/netfilter/nft_quota.c
@@ -140,11 +140,16 @@ static int nft_quota_do_dump(struct sk_buff *skb, struct nft_quota *priv,
 	u64 consumed, consumed_cap, quota;
 	u32 flags = priv->flags;
 
-	/* Since we inconditionally increment consumed quota for each packet
+	/* Since we unconditionally increment consumed quota for each packet
 	 * that we see, don't go over the quota boundary in what we send to
 	 * userspace.
 	 */
-	consumed = atomic64_read(priv->consumed);
+	if (reset) {
+		consumed = atomic64_xchg(priv->consumed, 0);
+		clear_bit(NFT_QUOTA_DEPLETED_BIT, &priv->flags);
+	} else {
+		consumed = atomic64_read(priv->consumed);
+	}
 	quota = atomic64_read(&priv->quota);
 	if (consumed >= quota) {
 		consumed_cap = quota;
@@ -160,10 +165,6 @@ static int nft_quota_do_dump(struct sk_buff *skb, struct nft_quota *priv,
 	    nla_put_be32(skb, NFTA_QUOTA_FLAGS, htonl(flags)))
 		goto nla_put_failure;
 
-	if (reset) {
-		atomic64_sub(consumed, priv->consumed);
-		clear_bit(NFT_QUOTA_DEPLETED_BIT, &priv->flags);
-	}
 	return 0;
 
 nla_put_failure:
-- 
2.52.0