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, 16 insertions, 5 deletions

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index bc0dab2593e..544f435d1af 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -804,6 +804,7 @@ int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	int corkreq = up->corkflag || msg->msg_flags&MSG_MORE;
 	int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);
 	struct sk_buff *skb;
+	struct ip_options_data opt_copy;
 
 	if (len > 0xFFFF)
 		return -EMSGSIZE;
@@ -877,22 +878,32 @@ int udp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 			free = 1;
 		connected = 0;
 	}
-	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();
+	}
 
 	saddr = ipc.addr;
 	ipc.addr = faddr = daddr;
 
-	if (ipc.opt && ipc.opt->srr) {
+	if (ipc.opt && ipc.opt->opt.srr) {
 		if (!daddr)
 			return -EINVAL;
-		faddr = ipc.opt->faddr;
+		faddr = ipc.opt->opt.faddr;
 		connected = 0;
 	}
 	tos = RT_TOS(inet->tos);
 	if (sock_flag(sk, SOCK_LOCALROUTE) ||
 	    (msg->msg_flags & MSG_DONTROUTE) ||
-	    (ipc.opt && ipc.opt->is_strictroute)) {
+	    (ipc.opt && ipc.opt->opt.is_strictroute)) {
 		tos |= RTO_ONLINK;
 		connected = 0;
 	}