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, 15 insertions, 4 deletions

diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index abf14db..a8659e0 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -460,6 +460,7 @@ static int raw_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	__be32 saddr;
 	u8  tos;
 	int err;
+	struct ip_options_data opt_copy;
 
 	err = -EMSGSIZE;
 	if (len > 0xFFFF)
@@ -520,8 +521,18 @@ static int raw_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	saddr = ipc.addr;
 	ipc.addr = daddr;
 
-	if (!ipc.opt)
-		ipc.opt = inet->opt;
+	if (!ipc.opt) {
+		struct ip_options_rcu *inet_opt;
+
+		rcu_read_lock();
+		inet_opt = rcu_dereference(inet->inet_opt);
+		if (inet_opt) {
+			memcpy(&opt_copy, inet_opt,
+			       sizeof(*inet_opt) + inet_opt->opt.optlen);
+			ipc.opt = &opt_copy.opt;
+		}
+		rcu_read_unlock();
+	}
 
 	if (ipc.opt) {
 		err = -EINVAL;
@@ -530,10 +541,10 @@ static int raw_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 		 */
 		if (inet->hdrincl)
 			goto done;
-		if (ipc.opt->srr) {
+		if (ipc.opt->opt.srr) {
 			if (!daddr)
 				goto done;
-			daddr = ipc.opt->faddr;
+			daddr = ipc.opt->opt.faddr;
 		}
 	}
 	tos = RT_CONN_FLAGS(sk);