Re: Why is /run/vm/by-id/${VM} writable by the VMM?

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 7/21/26 12:05, Alyssa Ross wrote:
> Demi Marie Obenour <demiobenour@gmail.com> writes:
> 
>> On 7/15/26 14:54, Alyssa Ross wrote:
>>> Demi Marie Obenour <demiobenour@gmail.com> writes:
>>>
>>>> On 7/13/26 05:04, Alyssa Ross wrote:
>>>>> Demi Marie Obenour <demiobenour@gmail.com> writes:
>>>>>
>>>>>> This seems to be a fairly significant hole in the VMM's sandbox.
>>>>>> Various code operates in that directory and isn't secure against
>>>>>> symlink attacks.
>>>>>>
>>>>>> Does the VMM really need write access to that directory?  Could it
>>>>>> be given access to a subdirectory that is mounted "nosymfollow"?
>>>>>
>>>>> I think it's just so it can create e.g. the serial file.  That could
>>>>> indeed be moved to a subdirectory.  The ideal solution is of course for
>>>>> Cloud Hypervisor to be able to accept every file it would otherwise
>>>>> create as an open file descriptor, which I expect will happen
>>>>> eventually.
>>>>
>>>> Should it be moved to a subdirectory for now?  That would make the
>>>> sandbox meaningful in practice.
>>>
>>> I suppose it could be.  Might make more sense to dedicate efforts
>>> towards fixing Cloud Hypervisor to accept file descriptors for the ~2
>>> paths it currently needs to create, though.  (That's obviously more
>>> work, but also more useful.)  If we were to work around this in
>>> Spectrum, we could keep symlinks outside the directory pointing into it,
>>> to keep paths nice and avoid churn once we can put them back in the
>>> parent directory.
>>
>> Do you happen to know which paths these are?
> 
> I think it might just be "serial"?  Not sure.

How difficult would it be to modify Cloud Hypervisor so this is passed
as a file descriptor?
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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