inet: add RCU protection to inet->opt

We lack proper synchronization to manipulate inet->opt ip_options

Problem is ip_make_skb() calls ip_setup_cork() and
ip_setup_cork() possibly makes a copy of ipc->opt (struct ip_options),
without any protection against another thread manipulating inet->opt.

Another thread can change inet->opt pointer and free old one under us.

Use RCU to protect inet->opt (changed to inet->inet_opt).

Instead of handling atomic refcounts, just copy ip_options when
necessary, to avoid cache line dirtying.

We cant insert an rcu_head in struct ip_options since its included in
skb->cb[], so this patch is large because I had to introduce a new
ip_options_rcu structure.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 20 deletions

diff --git a/net/ipv4/ip_options.c b/net/ipv4/ip_options.c
index 2391b24..01fc409 100644
--- a/net/ipv4/ip_options.c
+++ b/net/ipv4/ip_options.c
@@ -36,7 +36,7 @@
  * saddr is address of outgoing interface.
  */
 
-void ip_options_build(struct sk_buff * skb, struct ip_options * opt,
+void ip_options_build(struct sk_buff *skb, struct ip_options *opt,
 			    __be32 daddr, struct rtable *rt, int is_frag)
 {
 	unsigned char *iph = skb_network_header(skb);
@@ -83,9 +83,9 @@ void ip_options_build(struct sk_buff * skb, struct ip_options * opt,
  * NOTE: dopt cannot point to skb.
  */
 
-int ip_options_echo(struct ip_options * dopt, struct sk_buff * skb)
+int ip_options_echo(struct ip_options *dopt, struct sk_buff *skb)
 {
-	struct ip_options *sopt;
+	const struct ip_options *sopt;
 	unsigned char *sptr, *dptr;
 	int soffset, doffset;
 	int	optlen;
@@ -95,10 +95,8 @@ int ip_options_echo(struct ip_options * dopt, struct sk_buff * skb)
 
 	sopt = &(IPCB(skb)->opt);
 
-	if (sopt->optlen == 0) {
-		dopt->optlen = 0;
+	if (sopt->optlen == 0)
 		return 0;
-	}
 
 	sptr = skb_network_header(skb);
 	dptr = dopt->__data;
@@ -157,7 +155,7 @@ int ip_options_echo(struct ip_options * dopt, struct sk_buff * skb)
 		dopt->optlen += optlen;
 	}
 	if (sopt->srr) {
-		unsigned char * start = sptr+sopt->srr;
+		unsigned char *start = sptr+sopt->srr;
 		__be32 faddr;
 
 		optlen  = start[1];
@@ -499,19 +497,19 @@ void ip_options_undo(struct ip_options * opt)
 	}
 }
 
-static struct ip_options *ip_options_get_alloc(const int optlen)
+static struct ip_options_rcu *ip_options_get_alloc(const int optlen)
 {
-	return kzalloc(sizeof(struct ip_options) + ((optlen + 3) & ~3),
+	return kzalloc(sizeof(struct ip_options_rcu) + ((optlen + 3) & ~3),
 		       GFP_KERNEL);
 }
 
-static int ip_options_get_finish(struct net *net, struct ip_options **optp,
-				 struct ip_options *opt, int optlen)
+static int ip_options_get_finish(struct net *net, struct ip_options_rcu **optp,
+				 struct ip_options_rcu *opt, int optlen)
 {
 	while (optlen & 3)
-		opt->__data[optlen++] = IPOPT_END;
-	opt->optlen = optlen;
-	if (optlen && ip_options_compile(net, opt, NULL)) {
+		opt->opt.__data[optlen++] = IPOPT_END;
+	opt->opt.optlen = optlen;
+	if (optlen && ip_options_compile(net, &opt->opt, NULL)) {
 		kfree(opt);
 		return -EINVAL;
 	}
@@ -520,29 +518,29 @@ static int ip_options_get_finish(struct net *net, struct ip_options **optp,
 	return 0;
 }
 
-int ip_options_get_from_user(struct net *net, struct ip_options **optp,
+int ip_options_get_from_user(struct net *net, struct ip_options_rcu **optp,
 			     unsigned char __user *data, int optlen)
 {
-	struct ip_options *opt = ip_options_get_alloc(optlen);
+	struct ip_options_rcu *opt = ip_options_get_alloc(optlen);
 
 	if (!opt)
 		return -ENOMEM;
-	if (optlen && copy_from_user(opt->__data, data, optlen)) {
+	if (optlen && copy_from_user(opt->opt.__data, data, optlen)) {
 		kfree(opt);
 		return -EFAULT;
 	}
 	return ip_options_get_finish(net, optp, opt, optlen);
 }
 
-int ip_options_get(struct net *net, struct ip_options **optp,
+int ip_options_get(struct net *net, struct ip_options_rcu **optp,
 		   unsigned char *data, int optlen)
 {
-	struct ip_options *opt = ip_options_get_alloc(optlen);
+	struct ip_options_rcu *opt = ip_options_get_alloc(optlen);
 
 	if (!opt)
 		return -ENOMEM;
 	if (optlen)
-		memcpy(opt->__data, data, optlen);
+		memcpy(opt->opt.__data, data, optlen);
 	return ip_options_get_finish(net, optp, opt, optlen);
 }