[PATCH 3.16 298/370] packet: fix races in fanout_add()

Ben Hutchings
2017-03-10T13:25:12Z

From: Eric Dumazet <edumazet@google.com>

commit d199fab63c11998a602205f7ee7ff7c05c97164b upstream.

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>
[bwh: Backported to 3.16:
- No rollover queue stats
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1451,13 +1451,16 @@ static int fanout_add(struct sock *sk, u
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 &&
@@ -1513,17 +1516,16 @@ static void fanout_release(struct sock *
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);
}