Re: [PATCH] [PATCH net v2]vexy: Fix a use-after-free bug in vxge-main.c

[Jakub Kicinski]

On Thu, 16 Jun 2022 21:25:39 +0800 (CST) 梁文韬 wrote:
> >The driver is not called "vexy" as far as I can tell.
> >  
> >> The pointer vdev points to a memory region adjacent to a net_device
> >> structure ndev, which is a field of hldev. At line 4740, the invocation
> >> to vxge_device_unregister unregisters device hldev, and it also releases
> >> the memory region pointed by vdev->bar0. At line 4743, the freed memory
> >> region is referenced (i.e., iounmap(vdev->bar0)), resulting in a
> >> use-after-free vulnerability. We can fix the bug by calling iounmap
> >> before vxge_device_unregister.  
> >
> >Are you sure the bar0 is not needed by the netdev? You're freeing  
> >memory that the netdev may need until it's unregistered.  

> We try unregister the device in a patched kernel. The device is successfully
>  removed and there is not any warning or exception. See the following 
> snapshot. I use lspci to list pci devices, we can see that the device 
> (00:03.0 Unclassified ...Gigabit ethernet PCIe (rev 10)) is removed safely. 
> Thus, I believe that the bar0 is not needed when freeing the device.

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No errors happening during a test is not a sufficient proof of
correctness. You need to analyze the driver and figure out what bar0 
is used for.

Alternatively just save the address of bar0 to a local variable, let
the netdev unregister happen, and then call *unmap() on the local
variable. That won't move the unmap and avoid the UAF.

But please LMK how you use these cards first.

> /********************************************************************************/
> root@kernel:~# lspci
> 00:00.0 Host bridge: Intel Corporation 82G33/G31/P35/P31 Express DRAM 
> Controller
> 00:01.0 VGA compatible controller: Device 1234:1111 (rev 02)
> 00:02.0 Ethernet controller: Intel Corporation 82574L Gigabit Network 
> Connection
> 00:03.0 Unclassified device [00ff]: Exar Corp. X3100 Series 10 Gigabit 
> Ethernet PCIe (rev 10)

Is this a real NIC card, or just a emulated / virtualized one? 
Do you use it day to day? 

> 00:1d.0 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI 
> Controller #1 (rev 03)
> 00:1d.1 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI 
> Controller #2 (rev 03)
> 00:1d.2 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI 
> Controller #3 (rev 03)
> 00:1d.7 USB controller: Intel Corporation 82801I (ICH9 Family) USB2 EHCI 
> Controller #1 (rev 03)
> 00:1f.0 ISA bridge: Intel Corporation 82801IB (ICH9) LPC Interface 
> Controller (rev 02)
> 00:1f.2 SATA controller: Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6
>  port SATA Controller [AHCI mode] (rev 02)
> 00:1f.3 SMBus: Intel Corporation 82801I (ICH9 Family) SMBus Controller 
> (rev 02)
> root@kernel:~# echo 1 > /sys/bus/pci/devices/0000:00:03.0/remove
> root@kernel:~# lspci
> 00:00.0 Host bridge: Intel Corporation 82G33/G31/P35/P31 Express DRAM
>  Controller
> 00:01.0 VGA compatible controller: Device 1234:1111 (rev 02)
> 00:02.0 Ethernet controller: Intel Corporation 82574L Gigabit Network
>  Connection
> 00:1d.0 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI
>  Controller #1 (rev 03)
> 00:1d.1 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI
>  Controller #2 (rev 03)
> 00:1d.2 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI
>  Controller #3 (rev 03)
> 00:1d.7 USB controller: Intel Corporation 82801I (ICH9 Family) USB2 EHCI
>  Controller #1 (rev 03)
> 00:1f.0 ISA bridge: Intel Corporation 82801IB (ICH9) LPC Interface 
> Controller (rev 02)
> 00:1f.2 SATA controller: Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6 
> port SATA Controller [AHCI mode] (rev 02)
> 00:1f.3 SMBus: Intel Corporation 82801I (ICH9 Family) SMBus 
> Controller (rev 02)