netfilter: nf_ct_sane: remove pseudo skb linearization

For historical reason this code performs pseudo linearization of skbs
via skb_header_pointer and a global 64k buffer.

With arrival of BIG TCP, packets generated by TCP stack can exceed 64kb.

Rewrite this to only extract the needed header data. This also allows
to get rid of the locking.

Fixes: 7c4e983c4f3c ("net: allow gso_max_size to exceed 65536")
Fixes: 0fe79f28bfaf ("net: allow gro_max_size to exceed 65536")
Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nf_conntrack_sane.c

···
 MODULE_DESCRIPTION("SANE connection tracking helper");
 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
 
-static char *sane_buffer;
-
-static DEFINE_SPINLOCK(nf_sane_lock);
-
 #define MAX_PORTS 8
 static u_int16_t ports[MAX_PORTS];
 static unsigned int ports_c;
···
 	unsigned int dataoff, datalen;
 	const struct tcphdr *th;
 	struct tcphdr _tcph;
-	void *sb_ptr;
 	int ret = NF_ACCEPT;
 	int dir = CTINFO2DIR(ctinfo);
 	struct nf_ct_sane_master *ct_sane_info = nfct_help_data(ct);
 	struct nf_conntrack_expect *exp;
 	struct nf_conntrack_tuple *tuple;
-	struct sane_request *req;
 	struct sane_reply_net_start *reply;
+	union {
+		struct sane_request req;
+		struct sane_reply_net_start repl;
+	} buf;
 
 	/* Until there's been traffic both ways, don't look in packets. */
 	if (ctinfo != IP_CT_ESTABLISHED &&
···
 		return NF_ACCEPT;
 
 	datalen = skb->len - dataoff;
-
-	spin_lock_bh(&nf_sane_lock);
-	sb_ptr = skb_header_pointer(skb, dataoff, datalen, sane_buffer);
-	if (!sb_ptr) {
-		spin_unlock_bh(&nf_sane_lock);
-		return NF_ACCEPT;
-	}
-
 	if (dir == IP_CT_DIR_ORIGINAL) {
-		if (datalen != sizeof(struct sane_request))
-			goto out;
+		const struct sane_request *req;
 
-		req = sb_ptr;
+		if (datalen != sizeof(struct sane_request))
+			return NF_ACCEPT;
+
+		req = skb_header_pointer(skb, dataoff, datalen, &buf.req);
+		if (!req)
+			return NF_ACCEPT;
+
 		if (req->RPC_code != htonl(SANE_NET_START)) {
 			/* Not an interesting command */
-			ct_sane_info->state = SANE_STATE_NORMAL;
-			goto out;
+			WRITE_ONCE(ct_sane_info->state, SANE_STATE_NORMAL);
+			return NF_ACCEPT;
 		}
 
 		/* We're interested in the next reply */
-		ct_sane_info->state = SANE_STATE_START_REQUESTED;
-		goto out;
+		WRITE_ONCE(ct_sane_info->state, SANE_STATE_START_REQUESTED);
+		return NF_ACCEPT;
 	}
 
+	/* IP_CT_DIR_REPLY */
+
 	/* Is it a reply to an uninteresting command? */
-	if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
-		goto out;
+	if (READ_ONCE(ct_sane_info->state) != SANE_STATE_START_REQUESTED)
+		return NF_ACCEPT;
 
 	/* It's a reply to SANE_NET_START. */
-	ct_sane_info->state = SANE_STATE_NORMAL;
+	WRITE_ONCE(ct_sane_info->state, SANE_STATE_NORMAL);
 
 	if (datalen < sizeof(struct sane_reply_net_start)) {
 		pr_debug("NET_START reply too short\n");
-		goto out;
+		return NF_ACCEPT;
 	}
 
-	reply = sb_ptr;
+	datalen = sizeof(struct sane_reply_net_start);
+
+	reply = skb_header_pointer(skb, dataoff, datalen, &buf.repl);
+	if (!reply)
+		return NF_ACCEPT;
+
 	if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
 		/* saned refused the command */
 		pr_debug("unsuccessful SANE_STATUS = %u\n",
 			 ntohl(reply->status));
-		goto out;
+		return NF_ACCEPT;
 	}
 
 	/* Invalid saned reply? Ignore it. */
 	if (reply->zero != 0)
-		goto out;
+		return NF_ACCEPT;
 
 	exp = nf_ct_expect_alloc(ct);
 	if (exp == NULL) {
 		nf_ct_helper_log(skb, ct, "cannot alloc expectation");
-		ret = NF_DROP;
-		goto out;
+		return NF_DROP;
 	}
 
 	tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
···
 	}
 
 	nf_ct_expect_put(exp);
-
-out:
-	spin_unlock_bh(&nf_sane_lock);
 	return ret;
 }
 
···
 static void __exit nf_conntrack_sane_fini(void)
 {
 	nf_conntrack_helpers_unregister(sane, ports_c * 2);
-	kfree(sane_buffer);
 }
 
 static int __init nf_conntrack_sane_init(void)
···
 	int i, ret = 0;
 
 	NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_sane_master));
-
-	sane_buffer = kmalloc(65536, GFP_KERNEL);
-	if (!sane_buffer)
-		return -ENOMEM;
 
 	if (ports_c == 0)
 		ports[ports_c++] = SANE_PORT;
···
 	ret = nf_conntrack_helpers_register(sane, ports_c * 2);
 	if (ret < 0) {
 		pr_err("failed to register helpers\n");
-		kfree(sane_buffer);
 		return ret;
 	}