[PATCH] NETWORKING: avoid use IPCB in cipso_v4_error

[Nazarov Sergey <s-nazarov@yandex.ru>]

Since cipso_v4_error might be called from different network stack layers, we can't safely use icmp_send there.
icmp_send copies IP options with ip_option_echo, which uses IPCB to take access to IP header compiled data.
But after commit 971f10ec ("tcp: better TCP_SKB_CB layout to reduce cache line misses"), IPCB can't be used
above IP layer.
This patch fixes the problem by creating in cipso_v4_error a local copy of compiled IP options and using it with
introduced __icmp_send function. This looks some overloaded, but in quite rare error conditions only.

The original discussion is here:
https://lore.kernel.org/linux-security-module/16659801547571984@sas1-890ba5c2334a.qloud-c.yandex.net/

Signed-off-by: Sergey Nazarov <s-nazarov@yandex.ru>
---
 include/net/icmp.h    |    9 ++++++++-
 net/ipv4/cipso_ipv4.c |   18 ++++++++++++++++--
 net/ipv4/icmp.c       |    7 ++++---
 3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/include/net/icmp.h b/include/net/icmp.h
index 6ac3a5b..e0f709d 100644
--- a/include/net/icmp.h
+++ b/include/net/icmp.h
@@ -22,6 +22,7 @@
 
 #include <net/inet_sock.h>
 #include <net/snmp.h>
+#include <net/ip.h>
 
 struct icmp_err {
   int		errno;
@@ -39,7 +40,13 @@ struct icmp_err {
 struct sk_buff;
 struct net;
 
-void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info);
+void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
+		 const struct ip_options *opt);
+static inline void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
+{
+	__icmp_send(skb_in, type, code, info, &IPCB(skb_in)->opt);
+}
+
 int icmp_rcv(struct sk_buff *skb);
 int icmp_err(struct sk_buff *skb, u32 info);
 int icmp_init(void);
diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index 777fa3b..234d12e 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -1735,13 +1735,27 @@ int cipso_v4_validate(const struct sk_buff *skb, unsigned char **option)
  */
 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;
+
 	if (ip_hdr(skb)->protocol == IPPROTO_ICMP || error != -EACCES)
 		return;
 
+	/*
+	 * We might be called above the IP layer,
+	 * so we can not use icmp_send and IPCB here.
+	 */
+
+	memset(opt, 0, sizeof(struct ip_options));
+	opt->optlen = ip_hdr(skb)->ihl*4 - sizeof(struct iphdr);
+	memcpy(opt->__data, (unsigned char *)&(ip_hdr(skb)[1]), opt->optlen);
+	if (ip_options_compile(dev_net(skb->dev), opt, NULL))
+		return;
+
 	if (gateway)
-		icmp_send(skb, ICMP_DEST_UNREACH, ICMP_NET_ANO, 0);
+		__icmp_send(skb, ICMP_DEST_UNREACH, ICMP_NET_ANO, 0, opt);
 	else
-		icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_ANO, 0);
+		__icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_ANO, 0, opt);
 }
 
 /**
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 065997f..3f24414 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -570,7 +570,8 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb)
  *			MUST reply to only the first fragment.
  */
 
-void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
+void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
+		 const struct ip_options *opt)
 {
 	struct iphdr *iph;
 	int room;
@@ -691,7 +692,7 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
 					  iph->tos;
 	mark = IP4_REPLY_MARK(net, skb_in->mark);
 
-	if (ip_options_echo(net, &icmp_param.replyopts.opt.opt, skb_in))
+	if (__ip_options_echo(net, &icmp_param.replyopts.opt.opt, skb_in, opt))
 		goto out_unlock;
 
 
@@ -742,7 +743,7 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
 	local_bh_enable();
 out:;
 }
-EXPORT_SYMBOL(icmp_send);
+EXPORT_SYMBOL(__icmp_send);
 
 
 static void icmp_socket_deliver(struct sk_buff *skb, u32 info)
--