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Groups > linux.kernel > #1503662

[PATCH net-next] hv_netvsc: fix a race between netvsc_send() and netvsc_init_buf()

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Fix in commit 880988348270 ("hv_netvsc: set nvdev link after populating
chn_table") turns out to be incomplete. A crash in
netvsc_get_next_send_section() is observed on mtu change when the device
is under load. The race I identified is: if we get to netvsc_send() after
we set net_device_ctx->nvdev link in netvsc_device_add() but before we
finish netvsc_connect_vsp()->netvsc_init_buf() send_section_map is not
allocated and we crash. Unfortunately we can't set net_device_ctx->nvdev
link after the netvsc_init_buf() call as during the negotiation we need
to receive packets and on the receive path we check for it. It would
probably be possible to split nvdev into a pair of nvdev_in and nvdev_out
links and check them accordingly in get_outbound_net_device()/
get_inbound_net_device() but this looks like an overkill.

Check that send_section_map is allocated in netvsc_send().

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 drivers/net/hyperv/netvsc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index 720b5fa..e2bfaac 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -888,6 +888,13 @@ int netvsc_send(struct hv_device *device,
 	if (!net_device)
 		return -ENODEV;
 
+	/* We may race with netvsc_connect_vsp()/netvsc_init_buf() and get
+	 * here before the negotiation with the host is finished and
+	 * send_section_map may not be allocated yet.
+	 */
+	if (!net_device->send_section_map)
+		return -EAGAIN;
+
 	out_channel = net_device->chn_table[q_idx];
 
 	packet->send_buf_index = NETVSC_INVALID_INDEX;
-- 
2.7.4

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[PATCH net-next] hv_netvsc: fix a race between netvsc_send() and netvsc_init_buf() Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-10-19 16:30 +0200
  Re: [PATCH net-next] hv_netvsc: fix a race between netvsc_send() and netvsc_init_buf() Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-10-20 11:00 +0200
    Re: [PATCH net-next] hv_netvsc: fix a race between netvsc_send()  and netvsc_init_buf() David Miller <davem@davemloft.net> - 2016-10-20 20:10 +0200
      Re: [PATCH net-next] hv_netvsc: fix a race between netvsc_send() and netvsc_init_buf() Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-10-21 13:20 +0200
        Re: [PATCH net-next] hv_netvsc: fix a race between netvsc_send()  and netvsc_init_buf() David Miller <davem@davemloft.net> - 2016-10-21 17:00 +0200
          Re: [PATCH net-next] hv_netvsc: fix a race between netvsc_send() and netvsc_init_buf() Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-10-21 17:20 +0200
            Re: [PATCH net-next] hv_netvsc: fix a race between netvsc_send()  and netvsc_init_buf() David Miller <davem@davemloft.net> - 2016-10-21 17:30 +0200
  RE: [PATCH net-next] hv_netvsc: fix a race between netvsc_send() and  netvsc_init_buf() Stephen Hemminger <sthemmin@microsoft.com> - 2016-10-20 11:20 +0200
  Re: [PATCH net-next] hv_netvsc: fix a race between netvsc_send()  and netvsc_init_buf() David Miller <davem@davemloft.net> - 2016-10-21 17:30 +0200

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