netfilter: nf_tables: fix crash when nf_trace is enabled

do not access info->pkt when info->trace is not 1.
nft_traceinfo is not initialized, except when tracing is enabled.

The 'nft_trace_enabled' static key cannot be used for this, we must
always check info->trace first.

Pass nft_pktinfo directly to avoid this.

Fixes: e34b9ed9 ("netfilter: nf_tables: avoid skb access on nf_stolen")
Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/netfilter/nf_tables_core.c

@@ -34,25 +34,23 @@ static noinline void __nft_trace_packet(struct nft_traceinfo *info,
 	nft_trace_notify(info);
 }
 
-static inline void nft_trace_packet(struct nft_traceinfo *info,
+static inline void nft_trace_packet(const struct nft_pktinfo *pkt,
+				    struct nft_traceinfo *info,
 				    const struct nft_chain *chain,
 				    const struct nft_rule_dp *rule,
 				    enum nft_trace_types type)
 {
 	if (static_branch_unlikely(&nft_trace_enabled)) {
-		const struct nft_pktinfo *pkt = info->pkt;
-
 		info->nf_trace = pkt->skb->nf_trace;
 		info->rule = rule;
 		__nft_trace_packet(info, chain, type);
 	}
 }
 
-static inline void nft_trace_copy_nftrace(struct nft_traceinfo *info)
+static inline void nft_trace_copy_nftrace(const struct nft_pktinfo *pkt,
+					  struct nft_traceinfo *info)
 {
 	if (static_branch_unlikely(&nft_trace_enabled)) {
-		const struct nft_pktinfo *pkt = info->pkt;
-
 		if (info->trace)
 			info->nf_trace = pkt->skb->nf_trace;
 	}
@@ -96,7 +94,6 @@ static noinline void __nft_trace_verdict(struct nft_traceinfo *info,
 					 const struct nft_chain *chain,
 					 const struct nft_regs *regs)
 {
-	const struct nft_pktinfo *pkt = info->pkt;
 	enum nft_trace_types type;
 
 	switch (regs->verdict.code) {
@@ -110,7 +107,9 @@ static noinline void __nft_trace_verdict(struct nft_traceinfo *info,
 		break;
 	default:
 		type = NFT_TRACETYPE_RULE;
-		info->nf_trace = pkt->skb->nf_trace;
+
+		if (info->trace)
+			info->nf_trace = info->pkt->skb->nf_trace;
 		break;
 	}
 
@@ -271,10 +270,10 @@ nft_do_chain(struct nft_pktinfo *pkt, void *priv)
 		switch (regs.verdict.code) {
 		case NFT_BREAK:
 			regs.verdict.code = NFT_CONTINUE;
-			nft_trace_copy_nftrace(&info);
+			nft_trace_copy_nftrace(pkt, &info);
 			continue;
 		case NFT_CONTINUE:
-			nft_trace_packet(&info, chain, rule,
+			nft_trace_packet(pkt, &info, chain, rule,
 					 NFT_TRACETYPE_RULE);
 			continue;
 		}
@@ -318,7 +317,7 @@ nft_do_chain(struct nft_pktinfo *pkt, void *priv)
 		goto next_rule;
 	}
 
-	nft_trace_packet(&info, basechain, NULL, NFT_TRACETYPE_POLICY);
+	nft_trace_packet(pkt, &info, basechain, NULL, NFT_TRACETYPE_POLICY);
 
 	if (static_branch_unlikely(&nft_counters_enabled))
 		nft_update_chain_stats(basechain, pkt);