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>

8 files changed, 12 insertions, 46 deletions

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 2bfb2ad2fab1..877f682989b8 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -133,27 +133,18 @@ void rt6_clean_tohost(struct net *net, struct in6_addr *gateway);
 /*
  *      Store a destination cache entry in a socket
  */
-static inline void __ip6_dst_store(struct sock *sk, struct dst_entry *dst,
-                                   const struct in6_addr *daddr,
-                                   const struct in6_addr *saddr)
+static inline void ip6_dst_store(struct sock *sk, struct dst_entry *dst,
+                                 const struct in6_addr *daddr,
+                                 const struct in6_addr *saddr)
 {
         struct ipv6_pinfo *np = inet6_sk(sk);
-        struct rt6_info *rt = (struct rt6_info *) dst;
 
+        np->dst_cookie = rt6_get_cookie((struct rt6_info *)dst);
         sk_setup_caps(sk, dst);
         np->daddr_cache = daddr;
 #ifdef CONFIG_IPV6_SUBTREES
         np->saddr_cache = saddr;
 #endif
-        np->dst_cookie = rt6_get_cookie(rt);
-}
-
-static inline void ip6_dst_store(struct sock *sk, struct dst_entry *dst,
-                                 struct in6_addr *daddr, struct in6_addr *saddr)
-{
-        spin_lock(&sk->sk_dst_lock);
-        __ip6_dst_store(sk, dst, daddr, saddr);
-        spin_unlock(&sk->sk_dst_lock);
 }
 
 static inline bool ipv6_unicast_destination(const struct sk_buff *skb)
diff --git a/include/net/sock.h b/include/net/sock.h
index 0434138c5f95..52d27ee924f4 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -254,7 +254,6 @@ struct cg_proto;
   *     @sk_wq: sock wait queue and async head
   *     @sk_rx_dst: receive input route used by early demux
   *     @sk_dst_cache: destination cache
-  *     @sk_dst_lock: destination cache lock
   *     @sk_policy: flow policy
   *     @sk_receive_queue: incoming packets
   *     @sk_wmem_alloc: transmit queue bytes committed
@@ -393,7 +392,7 @@ struct sock {
 #endif
         struct dst_entry        *sk_rx_dst;
         struct dst_entry __rcu  *sk_dst_cache;
-        spinlock_t              sk_dst_lock;
+        /* Note: 32bit hole on 64bit arches */
         atomic_t                sk_wmem_alloc;
         atomic_t                sk_omem_alloc;
         int                     sk_sndbuf;
diff --git a/net/core/sock.c b/net/core/sock.c
index 9d79569935a3..e31dfcee1729 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1530,7 +1530,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
                 skb_queue_head_init(&newsk->sk_receive_queue);
                 skb_queue_head_init(&newsk->sk_write_queue);
 
-                spin_lock_init(&newsk->sk_dst_lock);
                 rwlock_init(&newsk->sk_callback_lock);
                 lockdep_set_class_and_name(&newsk->sk_callback_lock,
                                 af_callback_keys + newsk->sk_family,
@@ -1607,7 +1606,7 @@ void sk_setup_caps(struct sock *sk, struct dst_entry *dst)
 {
         u32 max_segs = 1;
 
-        __sk_dst_set(sk, dst);
+        sk_dst_set(sk, dst);
         sk->sk_route_caps = dst->dev->features;
         if (sk->sk_route_caps & NETIF_F_GSO)
                 sk->sk_route_caps |= NETIF_F_GSO_SOFTWARE;
@@ -2388,7 +2387,6 @@ void sock_init_data(struct socket *sock, struct sock *sk)
         } else
                 sk->sk_wq       =       NULL;
 
-        spin_lock_init(&sk->sk_dst_lock);
         rwlock_init(&sk->sk_callback_lock);
         lockdep_set_class_and_name(&sk->sk_callback_lock,
                         af_callback_keys + sk->sk_family,
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index e7e0b9bc2a43..9c6d0508e63a 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -459,7 +459,7 @@ static struct sock *dccp_v6_request_recv_sock(const struct sock *sk,
          * comment in that function for the gory details. -acme
          */
 
-        __ip6_dst_store(newsk, dst, NULL, NULL);
+        ip6_dst_store(newsk, dst, NULL, NULL);
         newsk->sk_route_caps = dst->dev->features & ~(NETIF_F_IP_CSUM |
                                                       NETIF_F_TSO);
         newdp6 = (struct dccp6_sock *)newsk;
@@ -883,7 +883,7 @@ static int dccp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
         np->saddr = *saddr;
         inet->inet_rcv_saddr = LOOPBACK4_IPV6;
 
-        __ip6_dst_store(sk, dst, NULL, NULL);
+        ip6_dst_store(sk, dst, NULL, NULL);
 
         icsk->icsk_ext_hdr_len = 0;
         if (opt)
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 38d66ddfb937..8ec0df75f1c4 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 36c5a98b0472..0a37ddc7af51 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 3ff5208772bb..a7ca2cde2ecb 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 6a50bb4a0dae..e7aab561b7b4 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;