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SubjectRE: [PATCH] net/cdc_ncm: fix null pointer panic at usbnet_link_change
Date
> From: Bjørn Mork [mailto:bjorn@mork.no]
> Sent: Tuesday, October 29, 2013 4:41 PM
> To: Du, ChangbinX
> Cc: oliver@neukum.org; linux-usb@vger.kernel.org; netdev@vger.kernel.org;
> linux-kernel@vger.kernel.org
> Subject: Re: [PATCH] net/cdc_ncm: fix null pointer panic at usbnet_link_change
>
> "Du, ChangbinX" <changbinx.du@intel.com> writes:
>
> > From: "Du, Changbin" <changbinx.du@intel.com>
> >
> > In cdc_ncm_bind() function, it call cdc_ncm_bind_common() to setup usb.
> > But cdc_ncm_bind_common() may meet error and cause usbnet_disconnect()
> > be called which calls free_netdev(net).
>
> I am sure you are right, but I really don't see how that can happen.
>
> AFAICS, we ensure that the intfdata is set to NULL before calling
> usb_driver_release_interface() in the error cleanup in
> cdc_ncm_bind_common():
>
>
> error2:
> usb_set_intfdata(ctx->control, NULL);
> usb_set_intfdata(ctx->data, NULL);
> if (ctx->data != ctx->control)
> usb_driver_release_interface(driver, ctx->data);
> error:
> cdc_ncm_free((struct cdc_ncm_ctx *)dev->data[0]);
> dev->data[0] = 0;
> dev_info(&dev->udev->dev, "bind() failure\n");
> return -ENODEV;
>
>
> Thus we hit the test in disconnect, and usbnet_disconnect() is never
> called:
>
> static void cdc_ncm_disconnect(struct usb_interface *intf)
> {
> struct usbnet *dev = usb_get_intfdata(intf);
>
> if (dev == NULL)
> return; /* already disconnected */
>
> usbnet_disconnect(intf);
> }
>
> So we should really be OK, but we are not???? I would appreciate it if
> anyone took the time to feed me why, with a very small spoon...
>

Yes, you are right. It should not happen if cdc_ncm_disconnect is not called. But this really happened.
It produced on kernel 3.10. Here is the full panic message for you to refer. I will get a method try to
reproduce it.

[ 15.635727] BUG: Bad page state in process khubd pfn:31994
[ 15.641989] page:f3ad9280 count:0 mapcount:0 mapping:00000020 index:0x0
[ 15.649384] page flags: 0x40000000()
[ 15.670096] BUG: unable to handle kernel NULL pointer dereference at 00000078
[ 15.678078] IP: [<c24b7f5e>] usbnet_link_change+0x1e/0x80
[ 15.684120] *pde = 00000000
[ 15.687339] Oops: 0000 [#1] SMP
[ 15.690953] Modules linked in: atmel_mxt_ts vxd392 videobuf_vmalloc videobuf_core bcm_bt_lpm bcm432)
[ 15.702658] CPU: 0 PID: 573 Comm: khubd Tainted: G B W O 3.10.1+ #1
[ 15.710241] task: f27e8f30 ti: f2084000 task.ti: f2084000
[ 15.716270] EIP: 0060:[<c24b7f5e>] EFLAGS: 00010246 CPU: 0
[ 15.722396] EIP is at usbnet_link_change+0x1e/0x80
[ 15.727747] EAX: f18524c0 EBX: 00000000 ECX: f18524c0 EDX: 00000000
[ 15.734746] ESI: f18524c0 EDI: 00000000 EBP: f2085b7c ESP: f2085b70
[ 15.741746] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
[ 15.747775] CR0: 8005003b CR2: 00000078 CR3: 02c3b000 CR4: 001007d0
[ 15.754774] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[ 15.761774] DR6: ffff0ff0 DR7: 00000400
[ 15.766054] Stack:
[ 15.768295] 00000000 f18524c0 c2a03818 f2085b8c c24bc69a f1852000 f1f52e00 f2085be0
[ 15.776991] c24b8d32 00000000 00000001 00000000 c2167f2c f2085bb4 c2821253 f2085bec
[ 15.785687] 00000246 00000246 f18d8088 f1f52e1c f1fce464 f1fce400 f18524c0 c28a06e0
[ 15.794376] Call Trace:
[ 15.797109] [<c24bc69a>] cdc_ncm_bind+0x3a/0x50
[ 15.802267] [<c24b8d32>] usbnet_probe+0x282/0x7d0
[ 15.807621] [<c2167f2c>] ? sysfs_new_dirent+0x6c/0x100
[ 15.813460] [<c2821253>] ? mutex_lock+0x13/0x40
[ 15.818618] [<c24bb278>] cdc_ncm_probe+0x8/0x10
[ 15.823777] [<c24e0ef7>] usb_probe_interface+0x187/0x2c0
[ 15.829811] [<c23caa8a>] ? driver_sysfs_add+0x6a/0x90
[ 15.835550] [<c23cb290>] ? __driver_attach+0x90/0x90
[ 15.841192] [<c23caf14>] driver_probe_device+0x74/0x360
[ 15.847127] [<c24e07b1>] ? usb_match_id+0x41/0x60
[ 15.852479] [<c24e081e>] ? usb_device_match+0x4e/0x90
[ 15.858219] [<c23cb290>] ? __driver_attach+0x90/0x90
[ 15.863861] [<c23cb2c9>] __device_attach+0x39/0x50
[ 15.869311] [<c23c93f4>] bus_for_each_drv+0x34/0x70
[ 15.874856] [<c23cae2b>] device_attach+0x7b/0x90
[ 15.880109] [<c23cb290>] ? __driver_attach+0x90/0x90
[ 15.885752] [<c23ca38f>] bus_probe_device+0x6f/0x90
[ 15.891298] [<c23c8a08>] device_add+0x558/0x630
[ 15.896457] [<c24e4821>] ? usb_create_ep_devs+0x71/0xd0
[ 15.902391] [<c24dd0db>] ? create_intf_ep_devs+0x4b/0x70
[ 15.908422] [<c24df2bf>] usb_set_configuration+0x4bf/0x800
[ 15.914648] [<c23cb290>] ? __driver_attach+0x90/0x90
[ 15.920292] [<c24e809b>] generic_probe+0x2b/0x90
[ 15.925546] [<c24e105c>] usb_probe_device+0x2c/0x70
[ 15.931091] [<c23caf14>] driver_probe_device+0x74/0x360
[ 15.943345] [<c2272102>] ? kobject_uevent_env+0x182/0x620
[ 15.949473] [<c2272102>] ? kobject_uevent_env+0x182/0x620
[ 15.955601] [<c23cb290>] ? __driver_attach+0x90/0x90
[ 15.961242] [<c23cb2c9>] __device_attach+0x39/0x50
[ 15.966692] [<c23c93f4>] bus_for_each_drv+0x34/0x70
[ 15.972238] [<c23cae2b>] device_attach+0x7b/0x90
[ 15.977492] [<c23cb290>] ? __driver_attach+0x90/0x90
[ 15.983135] [<c23ca38f>] bus_probe_device+0x6f/0x90
[ 15.988682] [<c23c8a08>] device_add+0x558/0x630
[ 15.993841] [<c2320b10>] ? add_device_randomness+0x60/0x70
[ 16.000069] [<c24d642f>] usb_new_device+0x1df/0x360
[ 16.005616] [<c24e81f6>] ? usb_detect_quirks+0x16/0x70
[ 16.011454] [<c24d7a9f>] hub_thread+0xd2f/0x1540
[ 16.016710] [<c20573a0>] ? finish_wait+0x60/0x60
[ 16.021965] [<c24d6d70>] ? hub_port_debounce+0x130/0x130
[ 16.027996] [<c2056f1f>] kthread+0x8f/0xa0
[ 16.032669] [<c282a237>] ret_from_kernel_thread+0x1b/0x28
[ 16.038798] [<c2056e90>] ? kthread_create_on_node+0xc0/0xc0
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