packet: fix races in fanout_add()

Multiple threads can call fanout_add() at the same time.

We need to grab fanout_mutex earlier to avoid races that could
lead to one thread freeing po->rollover that was set by another thread.

Do the same in fanout_release(), for peace of mind, and to help us
finding lockdep issues earlier.

Fixes: dc99f600698d ("packet: Add fanout support.")
Fixes: 0648ab70afe6 ("packet: rollover prepare: per-socket state")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index d56ee46b11fc9524e457e5fe8adf10c105a66ab6..0f03f6a53b4ddb8093a2122914200c0738af8fb3 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1619,6 +1619,7 @@ static void fanout_release_data(struct packet_fanout *f)
 
 static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
 {
+       struct packet_rollover *rollover = NULL;
        struct packet_sock *po = pkt_sk(sk);
        struct packet_fanout *f, *match;
        u8 type = type_flags & 0xff;
@@ -1641,23 +1642,28 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
                return -EINVAL;
        }
 
+       mutex_lock(&fanout_mutex);
+
+       err = -EINVAL;
        if (!po->running)
-               return -EINVAL;
+               goto out;
 
+       err = -EALREADY;
        if (po->fanout)
-               return -EALREADY;
+               goto out;
 
        if (type == PACKET_FANOUT_ROLLOVER ||
            (type_flags & PACKET_FANOUT_FLAG_ROLLOVER)) {
-               po->rollover = kzalloc(sizeof(*po->rollover), GFP_KERNEL);
-               if (!po->rollover)
-                       return -ENOMEM;
-               atomic_long_set(&po->rollover->num, 0);
-               atomic_long_set(&po->rollover->num_huge, 0);
-               atomic_long_set(&po->rollover->num_failed, 0);
+               err = -ENOMEM;
+               rollover = kzalloc(sizeof(*rollover), GFP_KERNEL);
+               if (!rollover)
+                       goto out;
+               atomic_long_set(&rollover->num, 0);
+               atomic_long_set(&rollover->num_huge, 0);
+               atomic_long_set(&rollover->num_failed, 0);
+               po->rollover = rollover;
        }
 
-       mutex_lock(&fanout_mutex);
        match = NULL;
        list_for_each_entry(f, &fanout_list, list) {
                if (f->id == id &&
@@ -1704,11 +1710,11 @@ static int fanout_add(struct sock *sk, u16 id, u16 type_flags)
                }
        }
 out:
-       mutex_unlock(&fanout_mutex);
-       if (err) {
-               kfree(po->rollover);
+       if (err && rollover) {
+               kfree(rollover);
                po->rollover = NULL;
        }
+       mutex_unlock(&fanout_mutex);
        return err;
 }
 
@@ -1717,23 +1723,22 @@ static void fanout_release(struct sock *sk)
        struct packet_sock *po = pkt_sk(sk);
        struct packet_fanout *f;
 
-       f = po->fanout;
-       if (!f)
-               return;
-
        mutex_lock(&fanout_mutex);
-       po->fanout = NULL;
+       f = po->fanout;
+       if (f) {
+               po->fanout = NULL;
+
+               if (atomic_dec_and_test(&f->sk_ref)) {
+                       list_del(&f->list);
+                       dev_remove_pack(&f->prot_hook);
+                       fanout_release_data(f);
+                       kfree(f);
+               }
 
-       if (atomic_dec_and_test(&f->sk_ref)) {
-               list_del(&f->list);
-               dev_remove_pack(&f->prot_hook);
-               fanout_release_data(f);
-               kfree(f);
+               if (po->rollover)
+                       kfree_rcu(po->rollover, rcu);
        }
        mutex_unlock(&fanout_mutex);
-
-       if (po->rollover)
-               kfree_rcu(po->rollover, rcu);
 }
 
 static bool packet_extra_vlan_len_allowed(const struct net_device *dev,