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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Mohammed Gamal <mgamal@redhat.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.4 137/222] hv_netvsc: Fix memory leak when removing rndis device
Date:   Wed, 22 Jan 2020 10:28:43 +0100
Message-Id: <20200122092843.549078478@linuxfoundation.org>
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From: Mohammed Gamal <mgamal@redhat.com>

[ Upstream commit 536dc5df2808efbefc5acee334d3c4f701790ec0 ]

kmemleak detects the following memory leak when hot removing
a network device:

unreferenced object 0xffff888083f63600 (size 256):
  comm "kworker/0:1", pid 12, jiffies 4294831717 (age 1113.676s)
  hex dump (first 32 bytes):
    00 40 c7 33 80 88 ff ff 00 00 00 00 10 00 00 00  .@.3............
    00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00  .....N..........
  backtrace:
    [<00000000d4a8f5be>] rndis_filter_device_add+0x117/0x11c0 [hv_netvsc]
    [<000000009c02d75b>] netvsc_probe+0x5e7/0xbf0 [hv_netvsc]
    [<00000000ddafce23>] vmbus_probe+0x74/0x170 [hv_vmbus]
    [<00000000046e64f1>] really_probe+0x22f/0xb50
    [<000000005cc35eb7>] driver_probe_device+0x25e/0x370
    [<0000000043c642b2>] bus_for_each_drv+0x11f/0x1b0
    [<000000005e3d09f0>] __device_attach+0x1c6/0x2f0
    [<00000000a72c362f>] bus_probe_device+0x1a6/0x260
    [<0000000008478399>] device_add+0x10a3/0x18e0
    [<00000000cf07b48c>] vmbus_device_register+0xe7/0x1e0 [hv_vmbus]
    [<00000000d46cf032>] vmbus_add_channel_work+0x8ab/0x1770 [hv_vmbus]
    [<000000002c94bb64>] process_one_work+0x919/0x17d0
    [<0000000096de6781>] worker_thread+0x87/0xb40
    [<00000000fbe7397e>] kthread+0x333/0x3f0
    [<000000004f844269>] ret_from_fork+0x3a/0x50

rndis_filter_device_add() allocates an instance of struct rndis_device
which never gets deallocated as rndis_filter_device_remove() sets
net_device->extension which points to the rndis_device struct to NULL,
leaving the rndis_device dangling.

Since net_device->extension is eventually freed in free_netvsc_device(),
we refrain from setting it to NULL inside rndis_filter_device_remove()

Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/hyperv/rndis_filter.c |    2 --
 1 file changed, 2 deletions(-)

--- a/drivers/net/hyperv/rndis_filter.c
+++ b/drivers/net/hyperv/rndis_filter.c
@@ -1436,8 +1436,6 @@ void rndis_filter_device_remove(struct h
 	/* Halt and release the rndis device */
 	rndis_filter_halt_device(net_dev, rndis_dev);
 
-	net_dev->extension = NULL;
-
 	netvsc_device_remove(dev);
 }