[PATCH 4.4 05/25] packet: fix races in fanout_add()

Greg Kroah-Hartman
2017-02-24T08:30:34Z

From: Eric Dumazet <edumazet@google.com>

[ 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.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/packet/af_packet.c | 53 ++++++++++++++++++++++++++-----------------------
1 file changed, 29 insertions(+), 24 deletions(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1623,6 +1623,7 @@ static void fanout_release_data(struct p

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;
@@ -1645,23 +1646,28 @@ 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;

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 &&
@@ -1708,11 +1714,11 @@ static int fanout_add(struct sock *sk, u
}
}
out:
- mutex_unlock(&fanout_mutex);
- if (err) {
- kfree(po->rollover);
+ if (err && rollover) {
+ kfree(rollover);
po->rollover = NULL;
}
+ mutex_unlock(&fanout_mutex);
return err;
}

@@ -1721,23 +1727,22 @@ static void fanout_release(struct sock *
struct packet_sock *po = pkt_sk(sk);
struct packet_fanout *f;

+ mutex_lock(&fanout_mutex);
f = po->fanout;
- if (!f)
- return;
+ if (f) {
+ po->fanout = NULL;

- mutex_lock(&fanout_mutex);
- 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,