ipv4: ensure rcu_read_lock() in cipso_v4_error()

BugLink: https://bugs.launchpad.net/bugs/1868629

commit 3e72dfdf upstream.

Similarly to commit c543cb4a ("ipv4: ensure rcu_read_lock() in
ipv4_link_failure()"), __ip_options_compile() must be called under rcu
protection.

Fixes: 3da1ed7a ("net: avoid use IPCB in cipso_v4_error")
Suggested-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Matteo Croce <mcroce@redhat.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

net/ipv4/cipso_ipv4.c

@@ -1809,6 +1809,7 @@ void cipso_v4_error(struct sk_buff *skb, int error, u32 gateway)
 {
 	unsigned char optbuf[sizeof(struct ip_options) + 40];
 	struct ip_options *opt = (struct ip_options *)optbuf;
+	int res;
 
 	if (ip_hdr(skb)->protocol == IPPROTO_ICMP || error != -EACCES)
 		return;
@@ -1820,7 +1821,11 @@ void cipso_v4_error(struct sk_buff *skb, int error, u32 gateway)
 
 	memset(opt, 0, sizeof(struct ip_options));
 	opt->optlen = ip_hdr(skb)->ihl*4 - sizeof(struct iphdr);
-	if (__ip_options_compile(dev_net(skb->dev), opt, skb, NULL))
+	rcu_read_lock();
+	res = __ip_options_compile(dev_net(skb->dev), opt, skb, NULL);
+	rcu_read_unlock();
+
+	if (res)
 		return;
 
 	if (gateway)