[PATCH net] netfilter: nf_tables: serialize offload stats with callback unbind

[Chengfeng Ye <nicoyip.dev@gmail.com>]

Rule GET and dump requests collect hardware statistics under RCU without
holding commit_mutex. Callback unbind removes entries from the base
chain's flow_block.cb_list and frees them immediately while holding
commit_mutex, so RCU does not protect the statistics iterator.

For example, a rule dump can load a block_cb in nft_setup_cb_call(),
then a concurrent transaction can unbind the chain and free that callback
in nft_flow_offload_unbind(). When the dump resumes, it dereferences the
freed block_cb to invoke its callback.

KASAN reported:

  BUG: KASAN: slab-use-after-free in nft_setup_cb_call.constprop.0+0x19d/0x200
  Read of size 8 at addr ffff88810a64d420 by task poc/87
  Call Trace:
   nft_setup_cb_call.constprop.0+0x19d/0x200
   nft_flow_offload_cmd+0x23b/0x480
   nft_flow_rule_stats+0x89/0x1d0
   nf_tables_fill_rule_info+0x689/0x8e0
   __nf_tables_dump_rules+0x256/0x940
   nf_tables_dump_rules+0x762/0x9f0
   netlink_dump+0x489/0x1140
  Allocated by task 86:
   flow_block_cb_setup_simple+0x443/0x820
   nft_block_offload_cmd+0x154/0x1e0
   nft_flow_block_chain+0xf9/0x420
   nft_flow_rule_offload_commit+0x448/0x5b0
  Freed by task 88:
   kfree+0x131/0x3c0
   nft_flow_offload_unbind+0x29c/0x400
   nft_block_offload_cmd+0x166/0x1e0
   nft_flow_block_chain+0xf9/0x420
   nft_flow_rule_offload_commit+0x18d/0x5b0

Use mutex_trylock() to serialize read-side hardware statistics refresh
with callback unbind. A blocking acquisition would sleep under RCU and
reintroduce the commit_mutex -> nfnl_subsys_ipset -> nlk_cb_mutex ->
commit_mutex lock dependency previously removed from reset dumps.

On contention, skip the hardware refresh and retain the cached counters,
as when the existing best-effort statistics request fails. Pass the
caller's lock state so transaction notifications continue to refresh
statistics under the mutex they already hold. Release an acquired mutex
before dumping expressions, leaving rule lookup and callback order intact.

Fixes: b72920f6e4a9 ("netfilter: nftables: counter hardware offload support")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
 net/netfilter/nf_tables_api.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index b59628e6240c..f234dc3f8d1e 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3780,7 +3780,7 @@ static int nf_tables_fill_rule_info(struct sk_buff *skb, struct net *net,
 				    const struct nft_table *table,
 				    const struct nft_chain *chain,
 				    const struct nft_rule *rule, u64 handle,
-				    bool reset)
+				    bool reset, bool commit_locked)
 {
 	struct nlmsghdr *nlh;
 	const struct nft_expr *expr, *next;
@@ -3806,8 +3806,15 @@ static int nf_tables_fill_rule_info(struct sk_buff *skb, struct net *net,
 			goto nla_put_failure;
 	}
 
-	if (chain->flags & NFT_CHAIN_HW_OFFLOAD)
-		nft_flow_rule_stats(chain, rule);
+	if (chain->flags & NFT_CHAIN_HW_OFFLOAD) {
+		struct nftables_pernet *nft_net = nft_pernet(net);
+
+		if (commit_locked || mutex_trylock(&nft_net->commit_mutex)) {
+			nft_flow_rule_stats(chain, rule);
+			if (!commit_locked)
+				mutex_unlock(&nft_net->commit_mutex);
+		}
+	}
 
 	list = nla_nest_start_noflag(skb, NFTA_RULE_EXPRESSIONS);
 	if (list == NULL)
@@ -3864,7 +3871,7 @@ static void nf_tables_rule_notify(const struct nft_ctx *ctx,
 
 	err = nf_tables_fill_rule_info(skb, ctx->net, ctx->portid, ctx->seq,
 				       event, flags, ctx->family, ctx->table,
-				       ctx->chain, rule, handle, false);
+				       ctx->chain, rule, handle, false, true);
 	if (err < 0) {
 		kfree_skb(skb);
 		goto err;
@@ -3924,7 +3931,8 @@ static int __nf_tables_dump_rules(struct sk_buff *skb,
 					NFT_MSG_NEWRULE,
 					NLM_F_MULTI | NLM_F_APPEND,
 					table->family,
-					table, chain, rule, handle, ctx->reset) < 0) {
+					table, chain, rule, handle,
+					ctx->reset, false) < 0) {
 			ret = 1;
 			break;
 		}
@@ -4072,7 +4080,7 @@ nf_tables_getrule_single(u32 portid, const struct nfnl_info *info,
 
 	err = nf_tables_fill_rule_info(skb2, net, portid,
 				       info->nlh->nlmsg_seq, NFT_MSG_NEWRULE, 0,
-				       family, table, chain, rule, 0, reset);
+				       family, table, chain, rule, 0, reset, false);
 	if (err < 0) {
 		kfree_skb(skb2);
 		return ERR_PTR(err);
-- 
2.43.0