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, 63 insertions, 50 deletions

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index a0af7ea..2b3c23c 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -1857,6 +1857,11 @@ static int cipso_v4_genopt(unsigned char *buf, u32 buf_len,
 	return CIPSO_V4_HDR_LEN + ret_val;
 }
 
+static void opt_kfree_rcu(struct rcu_head *head)
+{
+	kfree(container_of(head, struct ip_options_rcu, rcu));
+}
+
 /**
  * cipso_v4_sock_setattr - Add a CIPSO option to a socket
  * @sk: the socket
@@ -1879,7 +1884,7 @@ int cipso_v4_sock_setattr(struct sock *sk,
 	unsigned char *buf = NULL;
 	u32 buf_len;
 	u32 opt_len;
-	struct ip_options *opt = NULL;
+	struct ip_options_rcu *old, *opt = NULL;
 	struct inet_sock *sk_inet;
 	struct inet_connection_sock *sk_conn;
 
@@ -1915,22 +1920,25 @@ int cipso_v4_sock_setattr(struct sock *sk,
 		ret_val = -ENOMEM;
 		goto socket_setattr_failure;
 	}
-	memcpy(opt->__data, buf, buf_len);
-	opt->optlen = opt_len;
-	opt->cipso = sizeof(struct iphdr);
+	memcpy(opt->opt.__data, buf, buf_len);
+	opt->opt.optlen = opt_len;
+	opt->opt.cipso = sizeof(struct iphdr);
 	kfree(buf);
 	buf = NULL;
 
 	sk_inet = inet_sk(sk);
+
+	old = rcu_dereference_protected(sk_inet->inet_opt, sock_owned_by_user(sk));
 	if (sk_inet->is_icsk) {
 		sk_conn = inet_csk(sk);
-		if (sk_inet->opt)
-			sk_conn->icsk_ext_hdr_len -= sk_inet->opt->optlen;
-		sk_conn->icsk_ext_hdr_len += opt->optlen;
+		if (old)
+			sk_conn->icsk_ext_hdr_len -= old->opt.optlen;
+		sk_conn->icsk_ext_hdr_len += opt->opt.optlen;
 		sk_conn->icsk_sync_mss(sk, sk_conn->icsk_pmtu_cookie);
 	}
-	opt = xchg(&sk_inet->opt, opt);
-	kfree(opt);
+	rcu_assign_pointer(sk_inet->inet_opt, opt);
+	if (old)
+		call_rcu(&old->rcu, opt_kfree_rcu);
 
 	return 0;
 
@@ -1960,7 +1968,7 @@ int cipso_v4_req_setattr(struct request_sock *req,
 	unsigned char *buf = NULL;
 	u32 buf_len;
 	u32 opt_len;
-	struct ip_options *opt = NULL;
+	struct ip_options_rcu *opt = NULL;
 	struct inet_request_sock *req_inet;
 
 	/* We allocate the maximum CIPSO option size here so we are probably
@@ -1988,15 +1996,16 @@ int cipso_v4_req_setattr(struct request_sock *req,
 		ret_val = -ENOMEM;
 		goto req_setattr_failure;
 	}
-	memcpy(opt->__data, buf, buf_len);
-	opt->optlen = opt_len;
-	opt->cipso = sizeof(struct iphdr);
+	memcpy(opt->opt.__data, buf, buf_len);
+	opt->opt.optlen = opt_len;
+	opt->opt.cipso = sizeof(struct iphdr);
 	kfree(buf);
 	buf = NULL;
 
 	req_inet = inet_rsk(req);
 	opt = xchg(&req_inet->opt, opt);
-	kfree(opt);
+	if (opt)
+		call_rcu(&opt->rcu, opt_kfree_rcu);
 
 	return 0;
 
@@ -2016,34 +2025,34 @@ req_setattr_failure:
  * values on failure.
  *
  */
-static int cipso_v4_delopt(struct ip_options **opt_ptr)
+static int cipso_v4_delopt(struct ip_options_rcu **opt_ptr)
 {
 	int hdr_delta = 0;
-	struct ip_options *opt = *opt_ptr;
+	struct ip_options_rcu *opt = *opt_ptr;
 
-	if (opt->srr || opt->rr || opt->ts || opt->router_alert) {
+	if (opt->opt.srr || opt->opt.rr || opt->opt.ts || opt->opt.router_alert) {
 		u8 cipso_len;
 		u8 cipso_off;
 		unsigned char *cipso_ptr;
 		int iter;
 		int optlen_new;
 
-		cipso_off = opt->cipso - sizeof(struct iphdr);
-		cipso_ptr = &opt->__data[cipso_off];
+		cipso_off = opt->opt.cipso - sizeof(struct iphdr);
+		cipso_ptr = &opt->opt.__data[cipso_off];
 		cipso_len = cipso_ptr[1];
 
-		if (opt->srr > opt->cipso)
-			opt->srr -= cipso_len;
-		if (opt->rr > opt->cipso)
-			opt->rr -= cipso_len;
-		if (opt->ts > opt->cipso)
-			opt->ts -= cipso_len;
-		if (opt->router_alert > opt->cipso)
-			opt->router_alert -= cipso_len;
-		opt->cipso = 0;
+		if (opt->opt.srr > opt->opt.cipso)
+			opt->opt.srr -= cipso_len;
+		if (opt->opt.rr > opt->opt.cipso)
+			opt->opt.rr -= cipso_len;
+		if (opt->opt.ts > opt->opt.cipso)
+			opt->opt.ts -= cipso_len;
+		if (opt->opt.router_alert > opt->opt.cipso)
+			opt->opt.router_alert -= cipso_len;
+		opt->opt.cipso = 0;
 
 		memmove(cipso_ptr, cipso_ptr + cipso_len,
-			opt->optlen - cipso_off - cipso_len);
+			opt->opt.optlen - cipso_off - cipso_len);
 
 		/* determining the new total option length is tricky because of
 		 * the padding necessary, the only thing i can think to do at
@@ -2052,21 +2061,21 @@ static int cipso_v4_delopt(struct ip_options **opt_ptr)
 		 * from there we can determine the new total option length */
 		iter = 0;
 		optlen_new = 0;
-		while (iter < opt->optlen)
-			if (opt->__data[iter] != IPOPT_NOP) {
-				iter += opt->__data[iter + 1];
+		while (iter < opt->opt.optlen)
+			if (opt->opt.__data[iter] != IPOPT_NOP) {
+				iter += opt->opt.__data[iter + 1];
 				optlen_new = iter;
 			} else
 				iter++;
-		hdr_delta = opt->optlen;
-		opt->optlen = (optlen_new + 3) & ~3;
-		hdr_delta -= opt->optlen;
+		hdr_delta = opt->opt.optlen;
+		opt->opt.optlen = (optlen_new + 3) & ~3;
+		hdr_delta -= opt->opt.optlen;
 	} else {
 		/* only the cipso option was present on the socket so we can
 		 * remove the entire option struct */
 		*opt_ptr = NULL;
-		hdr_delta = opt->optlen;
-		kfree(opt);
+		hdr_delta = opt->opt.optlen;
+		call_rcu(&opt->rcu, opt_kfree_rcu);
 	}
 
 	return hdr_delta;
@@ -2083,15 +2092,15 @@ static int cipso_v4_delopt(struct ip_options **opt_ptr)
 void cipso_v4_sock_delattr(struct sock *sk)
 {
 	int hdr_delta;
-	struct ip_options *opt;
+	struct ip_options_rcu *opt;
 	struct inet_sock *sk_inet;
 
 	sk_inet = inet_sk(sk);
-	opt = sk_inet->opt;
-	if (opt == NULL || opt->cipso == 0)
+	opt = rcu_dereference_protected(sk_inet->inet_opt, 1);
+	if (opt == NULL || opt->opt.cipso == 0)
 		return;
 
-	hdr_delta = cipso_v4_delopt(&sk_inet->opt);
+	hdr_delta = cipso_v4_delopt(&sk_inet->inet_opt);
 	if (sk_inet->is_icsk && hdr_delta > 0) {
 		struct inet_connection_sock *sk_conn = inet_csk(sk);
 		sk_conn->icsk_ext_hdr_len -= hdr_delta;
@@ -2109,12 +2118,12 @@ void cipso_v4_sock_delattr(struct sock *sk)
  */
 void cipso_v4_req_delattr(struct request_sock *req)
 {
-	struct ip_options *opt;
+	struct ip_options_rcu *opt;
 	struct inet_request_sock *req_inet;
 
 	req_inet = inet_rsk(req);
 	opt = req_inet->opt;
-	if (opt == NULL || opt->cipso == 0)
+	if (opt == NULL || opt->opt.cipso == 0)
 		return;
 
 	cipso_v4_delopt(&req_inet->opt);
@@ -2184,14 +2193,18 @@ getattr_return:
  */
 int cipso_v4_sock_getattr(struct sock *sk, struct netlbl_lsm_secattr *secattr)
 {
-	struct ip_options *opt;
+	struct ip_options_rcu *opt;
+	int res = -ENOMSG;
 
-	opt = inet_sk(sk)->opt;
-	if (opt == NULL || opt->cipso == 0)
-		return -ENOMSG;
-
-	return cipso_v4_getattr(opt->__data + opt->cipso - sizeof(struct iphdr),
-				secattr);
+	rcu_read_lock();
+	opt = rcu_dereference(inet_sk(sk)->inet_opt);
+	if (opt && opt->opt.cipso)
+		res = cipso_v4_getattr(opt->opt.__data +
+						opt->opt.cipso -
+						sizeof(struct iphdr),
+				       secattr);
+	rcu_read_unlock();
+	return res;
 }
 
 /**