net/packet: fix a race in packet_set_ring() and packet_notifier()

When packet_set_ring() releases po->bind_lock, another thread can
run packet_notifier() and process an NETDEV_UP event.

This race and the fix are both similar to that of commit 15fe076edea7
("net/packet: fix a race in packet_bind() and packet_notifier()").

There too the packet_notifier NETDEV_UP event managed to run while a
po->bind_lock critical section had to be temporarily released. And
the fix was similarly to temporarily set po->num to zero to keep
the socket unhooked until the lock is retaken.

The po->bind_lock in packet_set_ring and packet_notifier precede the
introduction of git history.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Quang Le <quanglex97@gmail.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250801175423.2970334-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index bc438d0d96a7230df1d91734a91760ca291c52fa..a7017d7f09272058106181e95367080dc821da69 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -4573,10 +4573,10 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
        spin_lock(&po->bind_lock);
        was_running = packet_sock_flag(po, PACKET_SOCK_RUNNING);
        num = po->num;
-       if (was_running) {
-               WRITE_ONCE(po->num, 0);
+       WRITE_ONCE(po->num, 0);
+       if (was_running)
                __unregister_prot_hook(sk, false);
-       }
+
        spin_unlock(&po->bind_lock);
 
        synchronize_net();
@@ -4608,10 +4608,10 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
        mutex_unlock(&po->pg_vec_lock);
 
        spin_lock(&po->bind_lock);
-       if (was_running) {
-               WRITE_ONCE(po->num, num);
+       WRITE_ONCE(po->num, num);
+       if (was_running)
                register_prot_hook(sk);
-       }
+
        spin_unlock(&po->bind_lock);
        if (pg_vec && (po->tp_version > TPACKET_V2)) {
                /* Because we don't support block-based V3 on tx-ring */