[PATCH net, 2/2] hv_netvsc: Fix panic during namespace deletion with VF

[Haiyang Zhang <haiyangz@linux.microsoft.com>]

From: Haiyang Zhang <haiyangz@microsoft.com>

The existing code move the VF NIC to new namespace when NETDEV_REGISTER is
received on netvsc NIC. During deletion of the namespace,
default_device_exit_batch() >> default_device_exit_net() is called. When
netvsc NIC is moved back and registered to the default namespace, it
automatically brings VF NIC back to the default namespace. This will cause
the default_device_exit_net() >> for_each_netdev_safe loop unable to detect
the list end, and hit NULL ptr:

[  231.449420] mana 7870:00:00.0 enP30832s1: Moved VF to namespace with: eth0
[  231.449656] BUG: kernel NULL pointer dereference, address: 0000000000000010
[  231.450246] #PF: supervisor read access in kernel mode
[  231.450579] #PF: error_code(0x0000) - not-present page
[  231.450916] PGD 17b8a8067 P4D 0
[  231.451163] Oops: Oops: 0000 [#1] SMP NOPTI
[  231.451450] CPU: 82 UID: 0 PID: 1394 Comm: kworker/u768:1 Not tainted 6.16.0-rc4+ #3 VOLUNTARY
[  231.452042] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 11/21/2024
[  231.452692] Workqueue: netns cleanup_net
[  231.452947] RIP: 0010:default_device_exit_batch+0x16c/0x3f0
[  231.453326] Code: c0 0c f5 b3 e8 d5 db fe ff 48 85 c0 74 15 48 c7 c2 f8 fd ca b2 be 10 00 00 00 48 8d 7d c0 e8 7b 77 25 00 49 8b 86 28 01 00 00 <48> 8b 50 10 4c 8b 2a 4c 8d 62 f0 49 83 ed 10 4c 39 e0 0f 84 d6 00
[  231.454294] RSP: 0018:ff75fc7c9bf9fd00 EFLAGS: 00010246
[  231.454610] RAX: 0000000000000000 RBX: 0000000000000002 RCX: 61c8864680b583eb
[  231.455094] RDX: ff1fa9f71462d800 RSI: ff75fc7c9bf9fd38 RDI: 0000000030766564
[  231.455686] RBP: ff75fc7c9bf9fd78 R08: 0000000000000000 R09: 0000000000000000
[  231.456126] R10: 0000000000000001 R11: 0000000000000004 R12: ff1fa9f70088e340
[  231.456621] R13: ff1fa9f70088e340 R14: ffffffffb3f50c20 R15: ff1fa9f7103e6340
[  231.457161] FS:  0000000000000000(0000) GS:ff1faa6783a08000(0000) knlGS:0000000000000000
[  231.457707] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  231.458031] CR2: 0000000000000010 CR3: 0000000179ab2006 CR4: 0000000000b73ef0
[  231.458434] Call Trace:
[  231.458600]  <TASK>
[  231.458777]  ops_undo_list+0x100/0x220
[  231.459015]  cleanup_net+0x1b8/0x300
[  231.459285]  process_one_work+0x184/0x340

To fix it, skip the VF NIC's namespace change with netvsc when the VF
namespace is being cleaned up, because the default_device_exit_net() will
do it later.

Cc: stable@vger.kernel.org
Fixes: 4c262801ea60 ("hv_netvsc: Fix VF namespace also in synthetic NIC NETDEV_REGISTER event")
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
---
 drivers/net/hyperv/netvsc_drv.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 8be9bce66a4e..8fc05a8c0018 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -2788,13 +2788,21 @@ static void netvsc_event_set_vf_ns(struct net_device *ndev)
 {
 	struct net_device_context *ndev_ctx = netdev_priv(ndev);
 	struct net_device *vf_netdev;
+	struct net *vfnet;
 	int ret;
 
 	vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
 	if (!vf_netdev)
 		return;
 
-	if (!net_eq(dev_net(ndev), dev_net(vf_netdev))) {
+	vfnet = dev_net(vf_netdev);
+	/* Do not move it now if its net is being cleaned up,
+	 * net_cleanup_work will move it.
+	 */
+	if (llist_on_list(&vfnet->cleanup_list))
+		return;
+
+	if (!net_eq(dev_net(ndev), vfnet)) {
 		ret = dev_change_net_namespace(vf_netdev, dev_net(ndev),
 					       "eth%d");
 		if (ret)
-- 
2.34.1