Re: [edk2-devel] [PATCH] ShellPkg: Avoid corrupting installed device path protocols

["Ard Biesheuvel" <ardb@kernel.org>]

On Thu, 8 Dec 2022 at 19:28, Kinney, Michael D
<michael.d.kinney@intel.com> wrote:
>
> Hi Ard,
>
> From this description, it does not look like it should be modifying the
> contents of the device path.  Just point to the device path end node that
> follows the match found.
>
> /**
>   Gets the mapping that most closely matches the device path.
>
>   This function gets the mapping which corresponds to the device path *DevicePath. If
>   there is no exact match, then the mapping which most closely matches *DevicePath
>   is returned, and *DevicePath is updated to point to the remaining portion of the
>   device path. If there is an exact match, the mapping is returned and *DevicePath
>   points to the end-of-device-path node.
>
>   @param DevicePath             On entry, points to a device path pointer. On
>                                 exit, updates the pointer to point to the
>                                 portion of the device path after the mapping.
>
>   @retval NULL                  No mapping was found.
>   @return !=NULL                Pointer to NULL-terminated mapping. The buffer
>                                 is callee allocated and should be freed by the caller.
> **/
> CONST CHAR16 *
> EFIAPI
> EfiShellGetMapFromDevicePath (
>   IN OUT EFI_DEVICE_PATH_PROTOCOL  **DevicePath
>   );
>
> I see this API used in many places, and it looks like it would be
> destructive to any multi-instance device path. Multi-instance
> device paths are typically used for consoles, so we may not have
> noticed this destructive behavior with file system mapping paths.
>
> Did you try removing the call to SetDevicePathEndNode (*DevicePath);  ?
>

No, but that would be a functional change visible to all users of the
current API.

And note that the calling code already has 'DevicePathCopy' variables,
it just doesn't bother using them, so the intent is clearly to pass a
copy, not the actual device path.