tcp: connect() race with timewait reuse

Its currently possible that several threads issuing a connect() find
the same timewait socket and try to reuse it, leading to list
corruptions.

Condition for bug is that these threads bound their socket on same
address/port of to-be-find timewait socket, and connected to same
target. (SO_REUSEADDR needed)

To fix this problem, we could unhash timewait socket while holding
ehash lock, to make sure lookups/changes will be serialized. Only
first thread finds the timewait socket, other ones find the
established socket and return an EADDRNOTAVAIL error.

This second version takes into account Evgeniy's review and makes sure
inet_twsk_put() is called outside of locked sections.

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

diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h
index 4fd007f34dd50908b70af3a6f8b4ad2e7ba953d0..b801ade2295ef8af242b97a07393b63c35ab8195 100644 (file)
--- a/include/net/inet_timewait_sock.h
+++ b/include/net/inet_timewait_sock.h
@@ -199,6 +199,8 @@ static inline __be32 inet_rcv_saddr(const struct sock *sk)
 
 extern void inet_twsk_put(struct inet_timewait_sock *tw);
 
+extern int inet_twsk_unhash(struct inet_timewait_sock *tw);
+
 extern struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
                                                  const int state);
 

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 94ef51aa5bc9199fae46a0371e3b633d731322fd..21e5e32d8c600c192f53d8acec5f7bfeea5cfed5 100644 (file)
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -286,6 +286,7 @@ static int __inet_check_established(struct inet_timewait_death_row *death_row,
        struct sock *sk2;
        const struct hlist_nulls_node *node;
        struct inet_timewait_sock *tw;
+       int twrefcnt = 0;
 
        spin_lock(lock);
 
@@ -318,20 +319,23 @@ unique:
        sk->sk_hash = hash;
        WARN_ON(!sk_unhashed(sk));
        __sk_nulls_add_node_rcu(sk, &head->chain);
+       if (tw) {
+               twrefcnt = inet_twsk_unhash(tw);
+               NET_INC_STATS_BH(net, LINUX_MIB_TIMEWAITRECYCLED);
+       }
        spin_unlock(lock);
+       if (twrefcnt)
+               inet_twsk_put(tw);
        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 
        if (twp) {
                *twp = tw;
-               NET_INC_STATS_BH(net, LINUX_MIB_TIMEWAITRECYCLED);
        } else if (tw) {
                /* Silly. Should hash-dance instead... */
                inet_twsk_deschedule(tw, death_row);
-               NET_INC_STATS_BH(net, LINUX_MIB_TIMEWAITRECYCLED);
 
                inet_twsk_put(tw);
        }
-
        return 0;
 
 not_unique:

diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 31f931ef3daf1438f01d3f9bf3fd78aa6e085881..11a107a5af4f64d7a0e7159079941dc80359b2d4 100644 (file)
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -14,22 +14,33 @@
 #include <net/inet_timewait_sock.h>
 #include <net/ip.h>
 
+
+/*
+ * unhash a timewait socket from established hash
+ * lock must be hold by caller
+ */
+int inet_twsk_unhash(struct inet_timewait_sock *tw)
+{
+       if (hlist_nulls_unhashed(&tw->tw_node))
+               return 0;
+
+       hlist_nulls_del_rcu(&tw->tw_node);
+       sk_nulls_node_init(&tw->tw_node);
+       return 1;
+}
+
 /* Must be called with locally disabled BHs. */
 static void __inet_twsk_kill(struct inet_timewait_sock *tw,
                             struct inet_hashinfo *hashinfo)
 {
        struct inet_bind_hashbucket *bhead;
        struct inet_bind_bucket *tb;
+       int refcnt;
        /* Unlink from established hashes. */
        spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
 
        spin_lock(lock);
-       if (hlist_nulls_unhashed(&tw->tw_node)) {
-               spin_unlock(lock);
-               return;
-       }
-       hlist_nulls_del_rcu(&tw->tw_node);
-       sk_nulls_node_init(&tw->tw_node);
+       refcnt = inet_twsk_unhash(tw);
        spin_unlock(lock);
 
        /* Disassociate with bind bucket. */
@@ -37,9 +48,12 @@ static void __inet_twsk_kill(struct inet_timewait_sock *tw,
                        hashinfo->bhash_size)];
        spin_lock(&bhead->lock);
        tb = tw->tw_tb;
-       __hlist_del(&tw->tw_bind_node);
-       tw->tw_tb = NULL;
-       inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
+       if (tb) {
+               __hlist_del(&tw->tw_bind_node);
+               tw->tw_tb = NULL;
+               inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
+               refcnt++;
+       }
        spin_unlock(&bhead->lock);
 #ifdef SOCK_REFCNT_DEBUG
        if (atomic_read(&tw->tw_refcnt) != 1) {
@@ -47,7 +61,10 @@ static void __inet_twsk_kill(struct inet_timewait_sock *tw,
                       tw->tw_prot->name, tw, atomic_read(&tw->tw_refcnt));
        }
 #endif
-       inet_twsk_put(tw);
+       while (refcnt) {
+               inet_twsk_put(tw);
+               refcnt--;
+       }
 }
 
 static noinline void inet_twsk_free(struct inet_timewait_sock *tw)
@@ -92,6 +109,7 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
        tw->tw_tb = icsk->icsk_bind_hash;
        WARN_ON(!icsk->icsk_bind_hash);
        inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
+       atomic_inc(&tw->tw_refcnt);
        spin_unlock(&bhead->lock);
 
        spin_lock(lock);

diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index 00c6a3e6cddf51cb92a20bb42a3fe0b5985694f7..c813e294ec0c94d2aac13149f528683a85987d91 100644 (file)
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -223,6 +223,7 @@ static int __inet6_check_established(struct inet_timewait_death_row *death_row,
        struct sock *sk2;
        const struct hlist_nulls_node *node;
        struct inet_timewait_sock *tw;
+       int twrefcnt = 0;
 
        spin_lock(lock);
 
@@ -250,19 +251,23 @@ unique:
         * in hash table socket with a funny identity. */
        inet->inet_num = lport;
        inet->inet_sport = htons(lport);
+       sk->sk_hash = hash;
        WARN_ON(!sk_unhashed(sk));
        __sk_nulls_add_node_rcu(sk, &head->chain);
-       sk->sk_hash = hash;
+       if (tw) {
+               twrefcnt = inet_twsk_unhash(tw);
+               NET_INC_STATS_BH(net, LINUX_MIB_TIMEWAITRECYCLED);
+       }
        spin_unlock(lock);
+       if (twrefcnt)
+               inet_twsk_put(tw);
        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
 
-       if (twp != NULL) {
+       if (twp) {
                *twp = tw;
-               NET_INC_STATS_BH(net, LINUX_MIB_TIMEWAITRECYCLED);
-       } else if (tw != NULL) {
+       } else if (tw) {
                /* Silly. Should hash-dance instead... */
                inet_twsk_deschedule(tw, death_row);
-               NET_INC_STATS_BH(net, LINUX_MIB_TIMEWAITRECYCLED);
 
                inet_twsk_put(tw);
        }