[PATCH 3.2 084/147] packet: hold bind lock when rebinding to fanout hook

From: Ben Hutchings
Date: Mon Nov 06 2017 - 18:39:04 EST


3.2.95-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: Willem de Bruijn <willemb@xxxxxxxxxx>

commit 008ba2a13f2d04c947adc536d19debb8fe66f110 upstream.

Packet socket bind operations must hold the po->bind_lock. This keeps
po->running consistent with whether the socket is actually on a ptype
list to receive packets.

fanout_add unbinds a socket and its packet_rcv/tpacket_rcv call, then
binds the fanout object to receive through packet_rcv_fanout.

Make it hold the po->bind_lock when testing po->running and rebinding.
Else, it can race with other rebind operations, such as that in
packet_set_ring from packet_rcv to tpacket_rcv. Concurrent updates
can result in a socket being added to a fanout group twice, causing
use-after-free KASAN bug reports, among others.

Reported independently by both trinity and syzkaller.
Verified that the syzkaller reproducer passes after this patch.

Fixes: dc99f600698d ("packet: Add fanout support.")
Reported-by: nixioaming <nixiaoming@xxxxxxxxxx>
Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.2: use atomic_read() not refcount_read()]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
net/packet/af_packet.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1294,10 +1294,6 @@ static int fanout_add(struct sock *sk, u

mutex_lock(&fanout_mutex);

- err = -EINVAL;
- if (!po->running)
- goto out;
-
err = -EALREADY;
if (po->fanout)
goto out;
@@ -1334,7 +1330,10 @@ static int fanout_add(struct sock *sk, u
list_add(&match->list, &fanout_list);
}
err = -EINVAL;
- if (match->type == type &&
+
+ spin_lock(&po->bind_lock);
+ if (po->running &&
+ match->type == type &&
match->prot_hook.type == po->prot_hook.type &&
match->prot_hook.dev == po->prot_hook.dev) {
err = -ENOSPC;
@@ -1346,6 +1345,13 @@ static int fanout_add(struct sock *sk, u
err = 0;
}
}
+ spin_unlock(&po->bind_lock);
+
+ if (err && !atomic_read(&match->sk_ref)) {
+ list_del(&match->list);
+ kfree(match);
+ }
+
out:
mutex_unlock(&fanout_mutex);
return err;