packet: fix races in fanout_add()

[ Upstream commit d199fab63c11998a602205f7ee7ff7c05c97164b ]

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.

[js] no rollover in 3.12

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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 3c591a424bb6feae90a81a8bfe8c8ffeb014f96f..e5378d89cedc815fd7eb30249c622b796748e50f 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1316,13 +1316,16 @@ 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;
 
-       mutex_lock(&fanout_mutex);
        match = NULL;
        list_for_each_entry(f, &fanout_list, list) {
                if (f->id == id &&
@@ -1378,17 +1381,16 @@ 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);
-               kfree(f);
+               if (atomic_dec_and_test(&f->sk_ref)) {
+                       list_del(&f->list);
+                       dev_remove_pack(&f->prot_hook);
+                       kfree(f);
+               }
        }
        mutex_unlock(&fanout_mutex);
 }