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From:   Josh Elsasser <jelsasser@appneta.com>
To:     "David S. Miller" <davem@davemloft.net>
Cc:     josh@elsasser.ca, Josh Elsasser <jelsasser@appneta.com>,
        Edward Cree <ecree@solarflare.com>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Jiri Pirko <jiri@mellanox.com>,
        Petr Machata <petrm@mellanox.com>,
        Eric Dumazet <edumazet@google.com>,
        Amritha Nambiar <amritha.nambiar@intel.com>,
        Alexander Duyck <alexander.h.duyck@intel.com>,
        Li RongQing <lirongqing@baidu.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH net] net: set default network namespace in init_dummy_netdev()
Date:   Sat, 26 Jan 2019 14:38:33 -0800
Message-Id: <20190126223835.14613-1-jelsasser@appneta.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Assign a default net namespace to netdevs created by init_dummy_netdev().
Fixes a NULL pointer dereference caused by busy-polling a socket bound to
an iwlwifi wireless device, which bumps the per-net BUSYPOLLRXPACKETS stat
if napi_poll() received packets:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000190
  IP: napi_busy_loop+0xd6/0x200
  Call Trace:
    sock_poll+0x5e/0x80
    do_sys_poll+0x324/0x5a0
    SyS_poll+0x6c/0xf0
    do_syscall_64+0x6b/0x1f0
    entry_SYSCALL_64_after_hwframe+0x3d/0xa2

Fixes: 7db6b048da3b ("net: Commonize busy polling code to focus on napi_id instead of socket")
Signed-off-by: Josh Elsasser <jelsasser@appneta.com>
---
 net/core/dev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 82f20022259d..d1043d49979c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8712,7 +8712,9 @@ int init_dummy_netdev(struct net_device *dev)
 	set_bit(__LINK_STATE_PRESENT, &dev->state);
 	set_bit(__LINK_STATE_START, &dev->state);
 
+	/* napi_busy_loop stats accounting wants this */
+	dev_net_set(dev, &init_net);
+
 	/* Note : We dont allocate pcpu_refcnt for dummy devices,
 	 * because users of this 'device' dont need to change
 	 * its refcount.
-- 
2.19.1