Re: [PATCH] efivarfs: Limit the rate for non-root to read files

[Eric W. Biederman]

"Luck, Tony" <tony.luck@xxxxxxxxx> writes:

>>  - add a per-user mutex, and do the usleep inside of it, so that
>> anybody who tries to do a thousand threads will just be serialized by
>> the mutex.
>>
>> Note that the mutex needs to be per-user, because otherwise it will be
>> a DoS for the other users.
>
> I can try that tomorrow (adding the per-user mutex to struct user_struct
> right next to the ratelimit I added.

Another possibility is to cache the files in the page cache.  That will
reduce re-reads of the same data to the maximum extent.

If efi has a chance of changing variables behind our back we might want
something that would have a timeout on how long the data is cached,
and we probably want to make the caching policy write-trough not
write-back.

I just suggest this as it seems like a much more tried and true solution.

Eric