Filtering USB storage data in kernel module

Hi All,
I need to filter the data written/read to and from the USB storage disk.

Now the way USB is made known to OS is through SCSI and then respective filesystem ( mostly usbfs).

So is there any way I can intercept this stack and have my kernel module invoked so that I will get the data.

I have been thinking on two approaches:

1. Use VFS and write a proxy filesystem for USB device which will filter the data.
2. checking SCSI and any intercepting point.

Quoted 3 lines · Abhijit Pawar

Hi All,
I need to filter the data written/read to and from the USB storage disk.

Why?

What are you wanting to do at "filter" time?

Why just USB disks? What makes them special?

How are you going to determine if a disk is a USB device or not?

Quoted 2 lines

Now the way USB is made known to OS is through SCSI and then respective filesystem ( mostly usbfs).

Not really, usbfs is only one way, and it has nothing to do with usb disks.

Quoted 2 lines

So is there any way I can intercept this stack and have my kernel module invoked so that I will get the data.

Not easily.

Quoted 5 lines

I have been thinking on two approaches:

1. Use VFS and write a proxy filesystem for USB device which will filter the data.
2. checking SCSI and any intercepting point.

Again, what are you trying to "filter"? That will determine where you make changes.

Quoted 4 lines · Greg KH

Quoted 3 lines · Abhijit Pawar

Hi All,
I need to filter the data written/read to and from the USB storage disk.

Quoted 1 line

Why?

I want to build a secure machine with data protection. I want to have a security around the machine where anyone can attach a usb disk and copy the data. but i want to make the copied data useless unless it has the trust relation with the host to which its connected.
So if one has copied data from one secured machine and get that usb disk to other machine, he should see the encrypted garbage data.

Quoted 1 line

What are you wanting to do at "filter" time?

I want to encrypt the write data packets and decrypt the read data packets.

Quoted 1 line

Why just USB disks? What makes them special?

They are the one which can be attached to the system easily.

Quoted 1 line

How are you going to determine if a disk is a USB device or not?

Quoted 8 lines

Quoted 2 lines

Now the way USB is made known to OS is through SCSI and then respective filesystem ( mostly usbfs).

Not really, usbfs is only one way, and it has nothing to do with usb disks.

Quoted 2 lines

So is there any way I can intercept this stack and have my kernel module invoked so that I will get the data.

Not easily.

Even if its hard, can you please give details of how do I achieve this?

Quoted 2 lines

Quoted 2 lines

I have been thinking on two approaches:

Quoted 5 lines

Quoted 3 lines

1. Use VFS and write a proxy filesystem for USB device which will filter the data.
2. checking SCSI and any intercepting point.

Again, what are you trying to "filter"? That will determine where you make changes.

thanks, greg k-h
So what choice do I have now for this?

Quoted 5 lines · Abhijit Pawar

Quoted 4 lines · Greg KH

Quoted 3 lines · Abhijit Pawar

Hi All,
I need to filter the data written/read to and from the USB storage disk.

Quoted 8 lines

Quoted 1 line

Why?

I want to build a secure machine with data protection. I want to have a security around the machine where anyone can attach a usb disk and copy the data. but i want to make the copied data useless unless it has the trust relation with the host to which its connected.
So if one has copied data from one secured machine and get that usb disk to other machine, he should see the encrypted garbage data.

Interesting idea.

Quoted 5 lines

Quoted 1 line

What are you wanting to do at "filter" time?

I want to encrypt the write data packets and decrypt the read data packets.

Quoted 1 line

Why just USB disks? What makes them special?

They are the one which can be attached to the system easily.

Quoted 1 line

How are you going to determine if a disk is a USB device or not?

You forgot to answer this question :)

Quoted 15 lines

Quoted 9 lines

Quoted 3 lines

Now the way USB is made known to OS is through SCSI and then respective filesystem ( mostly usbfs).

Not really, usbfs is only one way, and it has nothing to do with usb disks.

Quoted 2 lines

So is there any way I can intercept this stack and have my kernel module invoked so that I will get the data.

Not easily.

Even if its hard, can you please give details of how do I achieve this?

Quoted 5 lines

Quoted 5 lines

I have been thinking on two approaches:

1. Use VFS and write a proxy filesystem for USB device which will filter the data.
2. checking SCSI and any intercepting point.

Quoted 4 lines

Quoted 2 lines

Again, what are you trying to "filter"? That will determine where you make changes.

thanks, greg k-h
So what choice do I have now for this?

Lots of work, best of luck with this task, it will not be simple or easy.

greg k-h

Quoted 16 lines · Greg KH

Quoted 5 lines · Abhijit Pawar

Quoted 4 lines · Greg KH

Quoted 3 lines · Abhijit Pawar

Hi All,
I need to filter the data written/read to and from the USB storage disk.

Quoted 8 lines

Quoted 1 line

Why?

I want to build a secure machine with data protection. I want to have a security around the machine where anyone can attach a usb disk and copy the data. but i want to make the copied data useless unless it has the trust relation with the host to which its connected.
So if one has copied data from one secured machine and get that usb disk to other machine, he should see the encrypted garbage data.

Interesting idea.

Quoted 7 lines

Quoted 6 lines

Quoted 1 line

What are you wanting to do at "filter" time?

I want to encrypt the write data packets and decrypt the read data packets.

Quoted 1 line

Why just USB disks? What makes them special?

They are the one which can be attached to the system easily.

Quoted 1 line

How are you going to determine if a disk is a USB device or not?

You forgot to answer this question :)

Yeah, I forgot that one. I am not very sure but if I can patch the USB core before it attaches the speficied class driver to the USB device. May be I can try and send some control request and get the class of the device. I think its not required as USB core itself will understand the class of the device and try to attach the proper driver. At this point of time, I will have some patch which will pass on the information to my module.
I am not sure if there are any intercepting points or any functions / structures exported in the USB core stack.

Quoted 25 lines

Quoted 14 lines

Quoted 10 lines

Quoted 3 lines

Now the way USB is made known to OS is through SCSI and then respective filesystem ( mostly usbfs).

Not really, usbfs is only one way, and it has nothing to do with usb disks.

Quoted 3 lines

So is there any way I can intercept this stack and have my kernel module
invoked so that I will get the data.

Not easily.

Even if its hard, can you please give details of how do I achieve this?

Quoted 2 lines

Quoted 2 lines

I have been thinking on two approaches:

Quoted 8 lines

Quoted 6 lines

Quoted 4 lines

1. Use VFS and write a proxy filesystem for USB device which will filter
the data.
2. checking SCSI and any intercepting point.

Again, what are you trying to "filter"? That will determine where you make changes.

thanks, greg k-h
So what choice do I have now for this?

Lots of work, best of luck with this task, it will not be simple or easy.

Quoted 1 line

greg k-h

Thanks. Its not that simple. I need to check the sCSI family code as well as USB core. Also VFS may be involved. :( :)

Regards,
Abhijit Pawar

Quoted 24 lines · Abhijit Pawar

Quoted 16 lines · Greg KH

Quoted 5 lines · Abhijit Pawar

Quoted 4 lines · Greg KH

Quoted 3 lines · Abhijit Pawar

Hi All,
I need to filter the data written/read to and from the USB storage disk.

Quoted 8 lines

Quoted 1 line

Why?

I want to build a secure machine with data protection. I want to have a security around the machine where anyone can attach a usb disk and copy the data. but i want to make the copied data useless unless it has the trust relation with the host to which its connected.
So if one has copied data from one secured machine and get that usb disk to other machine, he should see the encrypted garbage data.

Interesting idea.

Quoted 7 lines

Quoted 6 lines

Quoted 1 line

What are you wanting to do at "filter" time?

I want to encrypt the write data packets and decrypt the read data packets.

Quoted 1 line

Why just USB disks? What makes them special?

They are the one which can be attached to the system easily.

Quoted 1 line

How are you going to determine if a disk is a USB device or not?

You forgot to answer this question :)

Quoted 9 lines

Yeah, I forgot that one. I am not very sure but if I can patch the USB core before it attaches the speficied class driver to the USB device. May be I can try and send some control request and get the class of the device. I think its not required as USB core itself will understand the class of the device and try to attach the proper driver. At this point of time, I will have some patch which will pass on the information to my module.
I am not sure if there are any intercepting points or any functions / structures exported in the USB core stack.

It seems that the Linux notification chain should give me information whenever a USB device is added. I need to register for a notification callback in my module.

I have written a small module for this which uses the usb_register_notify()

Here is the debug trace from kernel when I add my logitech mouse to the system. I get the device added notification.

[30540.541134] usb 2-1.3: New USB device found, idVendor=046d, 
idProduct=c018
[30540.541143] usb 2-1.3: New USB device strings: Mfr=1, Product=2, 
SerialNumber=0
[30540.541150] usb 2-1.3: Product: USB Optical Mouse
[30540.541155] usb 2-1.3: Manufacturer: Logitech
[30540.541162] device: '2-1.3': device_add
[30540.541172] kobject: '2-1.3' (ffff8800252b0898): 
kobject_add_internal: parent: '2-1', set: 'devices'
[30540.549243] bus: 'usb': add device 2-1.3
[30540.549324] PM: Adding info for usb:2-1.3
[30540.549372] kobject: '2-1.3' (ffff8800252b0898): kobject_uevent_env
[30540.549384] kobject: '2-1.3' (ffff8800252b0898): fill_kobj_path: 
path = '/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3'
[30540.549473] bus: 'usb': driver_probe_device: matched device 2-1.3 
with driver usb
[30540.549482] bus: 'usb': really_probe: probing driver usb with 
device 2-1.3
[30540.549512] usb 2-1.3: rpm_resume flags 0x4
[30540.549518] usb 2-1.3: rpm_resume returns 1
[30540.550214] device: '2-1.3:1.0': device_add
[30540.550232] kobject: '2-1.3:1.0' (ffff880100648040): 
kobject_add_internal: parent: '2-1.3', set: 'devices'
[30540.550553] bus: 'usb': add device 2-1.3:1.0
[30540.550643] PM: Adding info for usb:2-1.3:1.0
[30540.550661] kobject: '2-1.3:1.0' (ffff880100648040): kobject_uevent_env
[30540.550678] kobject: '2-1.3:1.0' (ffff880100648040): 
fill_kobj_path: path = 
'/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0'
[30540.550905] bus: 'usb': driver_probe_device: matched device 
2-1.3:1.0 with driver usbserial_generic
[30540.550923] bus: 'usb': really_probe: probing driver 
usbserial_generic with device 2-1.3:1.0
[30540.551178] usb 2-1.3: rpm_resume flags 0x4
[30540.551189] usb 2-1.3: rpm_resume returns 1
[30540.551458] bus: 'usb': driver_probe_device: matched device 
2-1.3:1.0 with driver usbhid
[30540.551473] bus: 'usb': really_probe: probing driver usbhid with 
device 2-1.3:1.0
[30540.551513] usb 2-1.3: rpm_resume flags 0x4
[30540.551523] usb 2-1.3: rpm_resume returns 1
[30540.552922] device: '0003:046D:C018.0002': device_add
[30540.552939] kobject: '0003:046D:C018.0002' (ffff88012b5b9898): 
kobject_add_internal: parent: '2-1.3:1.0', set: 'devices'
[30540.552981] bus: 'hid': add device 0003:046D:C018.0002
[30540.553143] PM: Adding info for hid:0003:046D:C018.0002
[30540.553159] kobject: '0003:046D:C018.0002' (ffff88012b5b9898): 
kobject_uevent_env
[30540.553176] kobject: '0003:046D:C018.0002' (ffff88012b5b9898): 
fill_kobj_path: path = 
'/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/0003:046D:C018.0002'
[30540.553352] bus: 'hid': driver_probe_device: matched device 
0003:046D:C018.0002 with driver generic-usb
[30540.553369] bus: 'hid': really_probe: probing driver generic-usb 
with device 0003:046D:C018.0002
[30540.555608] device: 'input17': device_add
[30540.555628] kobject: 'input' (ffff8800619af5a0): 
kobject_add_internal: parent: '2-1.3:1.0', set: '(null)'
[30540.555677] kobject: 'input17' (ffff8800252b5b58): 
kobject_add_internal: parent: 'input', set: 'devices'
[30540.555879] PM: Adding info for No Bus:input17
[30540.555888] kobject: 'input17' (ffff8800252b5b58): kobject_uevent_env
[30540.555899] kobject: 'input17' (ffff8800252b5b58): fill_kobj_path: 
path = 
'/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/input/input17'
[30540.556072] kobject: 'input17' (ffff8800252b5b58): fill_kobj_path: 
path = 
'/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/input/input17'
[30540.556087] input: Logitech USB Optical Mouse as 
/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/input/input17
[30540.556140] device: 'mouse0': device_add
[30540.556153] kobject: 'mouse0' (ffff8800252b41b8): 
kobject_add_internal: parent: 'input17', set: 'devices'
[30540.556907] PM: Adding info for No Bus:mouse0
[30540.556924] kobject: 'mouse0' (ffff8800252b41b8): kobject_uevent_env
[30540.556940] kobject: 'mouse0' (ffff8800252b41b8): fill_kobj_path: 
path = 
'/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/input/input17/mouse0'
[30540.557125] device: 'event6': device_add
[30540.557139] kobject: 'event6' (ffff8800252b21c0): 
kobject_add_internal: parent: 'input17', set: 'devices'
[30540.558939] PM: Adding info for No Bus:event6
[30540.558953] kobject: 'event6' (ffff8800252b21c0): kobject_uevent_env
[30540.558969] kobject: 'event6' (ffff8800252b21c0): fill_kobj_path: 
path = 
'/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/input/input17/event6'
[30540.559198] device: 'hidraw0': device_add
[30540.559221] kobject: 'hidraw' (ffff8800619afa20): 
kobject_add_internal: parent: '0003:046D:C018.0002', set: '(null)'
[30540.559252] kobject: 'hidraw0' (ffff88012bfbc810): 
kobject_add_internal: parent: 'hidraw', set: 'devices'
[30540.559281] usbhid 2-1.3:1.0: rpm_resume flags 0x4
[30540.559293] usbhid 2-1.3:1.0: rpm_resume returns 1
[30540.559655] PM: Adding info for No Bus:hidraw0
[30540.559670] kobject: 'hidraw0' (ffff88012bfbc810): kobject_uevent_env
[30540.559687] kobject: 'hidraw0' (ffff88012bfbc810): fill_kobj_path: 
path = 
'/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.3/2-1.3:1.0/0003:046D:C018.0002/hidraw/hidraw0'
[30540.559805] generic-usb 0003:046D:C018.0002: input,hidraw0: USB HID 
v1.11 Mouse [Logitech USB Optical Mouse] on usb-0000:00:1d.0-1.3/input0
[30540.559820] driver: '0003:046D:C018.0002': driver_bound: bound to 
device 'generic-usb'
[30540.559833] bus: 'hid': really_probe: bound device 
0003:046D:C018.0002 to driver generic-usb
[30540.559859] driver: '2-1.3:1.0': driver_bound: bound to device 'usbhid'
[30540.559874] bus: 'usb': really_probe: bound device 2-1.3:1.0 to 
driver usbhid
[30540.559892] usbhid 2-1.3:1.0: rpm_suspend flags 0x4
[30540.559908] usbhid 2-1.3:1.0: rpm_suspend returns 0
[30540.559939] device: 'ep_81': device_add
[30540.559950] kobject: 'ep_81' (ffff88009613f820): 
kobject_add_internal: parent: '2-1.3:1.0', set: 'devices'
[30540.560175] PM: Adding info for No Bus:ep_81
[30540.560189] kobject: 'ep_81' (ffff88009613f820): kobject_uevent_env
[30540.560198] kobject: 'ep_81' (ffff88009613f820): 
kobject_uevent_env: filter function caused the event to drop!
[30540.561372] usb_notify_subscriber
[30540.561378] usb_notify_subscriber:USB device added

So this notification is raised when everything is done by the USB core and it has already attached the driver to the device. In that case I think this is not that important and will not solve the purpose which I am looking for.

Quoted 32 lines

Quoted 21 lines

Quoted 21 lines

Quoted 10 lines

Quoted 3 lines

Now the way USB is made known to OS is through SCSI and then respective filesystem ( mostly usbfs).

Not really, usbfs is only one way, and it has nothing to do with usb disks.

Quoted 3 lines

So is there any way I can intercept this stack and have my kernel module
invoked so that I will get the data.

Not easily.

Even if its hard, can you please give details of how do I achieve this?

Quoted 9 lines

Quoted 6 lines

I have been thinking on two approaches:

1. Use VFS and write a proxy filesystem for USB device which will filter
the data.
2. checking SCSI and any intercepting point.

Again, what are you trying to "filter"? That will determine where you
make changes.

Quoted 6 lines

Quoted 2 lines

thanks, greg k-h
So what choice do I have now for this?

Lots of work, best of luck with this task, it will not be simple or easy.

greg k-h

Thanks. Its not that simple. I need to check the sCSI family code as well as USB core. Also VFS may be involved. :( :)

Regards,
Abhijit Pawar