tcp: Fix a connect() race with timewait sockets

First patch changes __inet_hash_nolisten() and __inet6_hash()
to get a timewait parameter to be able to unhash it from ehash
at same time the new socket is inserted in hash.

This makes sure timewait socket wont be found by a concurrent
writer in __inet_check_established()

Reported-by: kapil dakhane <kdakhane@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 17 insertions, 7 deletions

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 21e5e32d8c60..c4201b7ece38 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -351,12 +351,13 @@ static inline u32 inet_sk_port_offset(const struct sock *sk)
                                           inet->inet_dport);
 }
 
-void __inet_hash_nolisten(struct sock *sk)
+int __inet_hash_nolisten(struct sock *sk, struct inet_timewait_sock *tw)
 {
         struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
         struct hlist_nulls_head *list;
         spinlock_t *lock;
         struct inet_ehash_bucket *head;
+        int twrefcnt = 0;
 
         WARN_ON(!sk_unhashed(sk));
 
@@ -367,8 +368,13 @@ void __inet_hash_nolisten(struct sock *sk)
 
         spin_lock(lock);
         __sk_nulls_add_node_rcu(sk, list);
+        if (tw) {
+                WARN_ON(sk->sk_hash != tw->tw_hash);
+                twrefcnt = inet_twsk_unhash(tw);
+        }
         spin_unlock(lock);
         sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
+        return twrefcnt;
 }
 EXPORT_SYMBOL_GPL(__inet_hash_nolisten);
 
@@ -378,7 +384,7 @@ static void __inet_hash(struct sock *sk)
         struct inet_listen_hashbucket *ilb;
 
         if (sk->sk_state != TCP_LISTEN) {
-                __inet_hash_nolisten(sk);
+                __inet_hash_nolisten(sk, NULL);
                 return;
         }
 
@@ -427,7 +433,7 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
                 struct sock *sk, u32 port_offset,
                 int (*check_established)(struct inet_timewait_death_row *,
                         struct sock *, __u16, struct inet_timewait_sock **),
-                void (*hash)(struct sock *sk))
+                int (*hash)(struct sock *sk, struct inet_timewait_sock *twp))
 {
         struct inet_hashinfo *hinfo = death_row->hashinfo;
         const unsigned short snum = inet_sk(sk)->inet_num;
@@ -435,6 +441,7 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
         struct inet_bind_bucket *tb;
         int ret;
         struct net *net = sock_net(sk);
+        int twrefcnt = 1;
 
         if (!snum) {
                 int i, remaining, low, high, port;
@@ -493,13 +500,16 @@ ok:
                 inet_bind_hash(sk, tb, port);
                 if (sk_unhashed(sk)) {
                         inet_sk(sk)->inet_sport = htons(port);
-                        hash(sk);
+                        twrefcnt += hash(sk, tw);
                 }
                 spin_unlock(&head->lock);
 
                 if (tw) {
                         inet_twsk_deschedule(tw, death_row);
-                        inet_twsk_put(tw);
+                        while (twrefcnt) {
+                                twrefcnt--;
+                                inet_twsk_put(tw);
+                        }
                 }
 
                 ret = 0;
@@ -510,7 +520,7 @@ ok:
         tb  = inet_csk(sk)->icsk_bind_hash;
         spin_lock_bh(&head->lock);
         if (sk_head(&tb->owners) == sk && !sk->sk_bind_node.next) {
-                hash(sk);
+                hash(sk, NULL);
                 spin_unlock_bh(&head->lock);
                 return 0;
         } else {
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 29002ab26e0d..15e96030ce47 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1464,7 +1464,7 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
         }
 #endif
 
-        __inet_hash_nolisten(newsk);
+        __inet_hash_nolisten(newsk, NULL);
         __inet_inherit_port(sk, newsk);
 
         return newsk;