ipv6: kill sk_dst_lock

While testing the np->opt RCU conversion, I found that UDP/IPv6 was
using a mixture of xchg() and sk_dst_lock to protect concurrent changes
to sk->sk_dst_cache, leading to possible corruptions and crashes.

ip6_sk_dst_lookup_flow() uses sk_dst_check() anyway, so the simplest
way to fix the mess is to remove sk_dst_lock completely, as we did for
IPv4.

__ip6_dst_store() and ip6_dst_store() share same implementation.

sk_setup_caps() being called with socket lock being held or not,
we have to use sk_dst_set() instead of __sk_dst_set()

Note that I had to move the "np->dst_cookie = rt6_get_cookie(rt);"
in ip6_dst_store() before the sk_setup_caps(sk, dst) call.

This is because ip6_dst_store() can be called from process context,
without any lock held.

As soon as the dst is installed in sk->sk_dst_cache, dst can be freed
from another cpu doing a concurrent ip6_dst_store()

Doing the dst dereference before doing the install is needed to make
sure no use after free would trigger.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 4 insertions, 26 deletions

diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 38d66dd..8ec0df7 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -673,7 +673,7 @@ int inet6_sk_rebuild_header(struct sock *sk)
 			return PTR_ERR(dst);
 		}
 
-		__ip6_dst_store(sk, dst, NULL, NULL);
+		ip6_dst_store(sk, dst, NULL, NULL);
 	}
 
 	return 0;
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 36c5a98..0a37ddc 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -834,11 +834,6 @@ void icmpv6_flow_init(struct sock *sk, struct flowi6 *fl6,
 	security_sk_classify_flow(sk, flowi6_to_flowi(fl6));
 }
 
-/*
- * Special lock-class for __icmpv6_sk:
- */
-static struct lock_class_key icmpv6_socket_sk_dst_lock_key;
-
 static int __net_init icmpv6_sk_init(struct net *net)
 {
 	struct sock *sk;
@@ -860,15 +855,6 @@ static int __net_init icmpv6_sk_init(struct net *net)
 
 		net->ipv6.icmp_sk[i] = sk;
 
-		/*
-		 * Split off their lock-class, because sk->sk_dst_lock
-		 * gets used from softirqs, which is safe for
-		 * __icmpv6_sk (because those never get directly used
-		 * via userspace syscalls), but unsafe for normal sockets.
-		 */
-		lockdep_set_class(&sk->sk_dst_lock,
-				  &icmpv6_socket_sk_dst_lock_key);
-
 		/* Enough space for 2 64K ICMP packets, including
 		 * sk_buff struct overhead.
 		 */
diff --git a/net/ipv6/inet6_connection_sock.c b/net/ipv6/inet6_connection_sock.c
index 3ff5208..a7ca2cd 100644
--- a/net/ipv6/inet6_connection_sock.c
+++ b/net/ipv6/inet6_connection_sock.c
@@ -111,14 +111,6 @@ void inet6_csk_addr2sockaddr(struct sock *sk, struct sockaddr *uaddr)
 EXPORT_SYMBOL_GPL(inet6_csk_addr2sockaddr);
 
 static inline
-void __inet6_csk_dst_store(struct sock *sk, struct dst_entry *dst,
-			   const struct in6_addr *daddr,
-			   const struct in6_addr *saddr)
-{
-	__ip6_dst_store(sk, dst, daddr, saddr);
-}
-
-static inline
 struct dst_entry *__inet6_csk_dst_check(struct sock *sk, u32 cookie)
 {
 	return __sk_dst_check(sk, cookie);
@@ -153,7 +145,7 @@ static struct dst_entry *inet6_csk_route_socket(struct sock *sk,
 		dst = ip6_dst_lookup_flow(sk, fl6, final_p);
 
 		if (!IS_ERR(dst))
-			__inet6_csk_dst_store(sk, dst, NULL, NULL);
+			ip6_dst_store(sk, dst, NULL, NULL);
 	}
 	return dst;
 }
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 6a50bb4..e7aab56 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -257,7 +257,7 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 	inet->inet_rcv_saddr = LOOPBACK4_IPV6;
 
 	sk->sk_gso_type = SKB_GSO_TCPV6;
-	__ip6_dst_store(sk, dst, NULL, NULL);
+	ip6_dst_store(sk, dst, NULL, NULL);
 
 	if (tcp_death_row.sysctl_tw_recycle &&
 	    !tp->rx_opt.ts_recent_stamp &&
@@ -1060,7 +1060,7 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
 	 */
 
 	newsk->sk_gso_type = SKB_GSO_TCPV6;
-	__ip6_dst_store(newsk, dst, NULL, NULL);
+	ip6_dst_store(newsk, dst, NULL, NULL);
 	inet6_sk_rx_dst_set(newsk, skb);
 
 	newtcp6sk = (struct tcp6_sock *)newsk;