linux-kernel - Re: [PATCH v2] io_uring/rsrc: fix RLIMIT_MEMLOCK bypass by removing cross-buffer accounting

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Message-ID: <2919f3c5-2510-4e97-ab7f-c9eef1c76a69@kernel.dk>
Date: Mon, 19 Jan 2026 16:40:13 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Yuhao Jiang <danisjiang@...il.com>
Cc: Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] io_uring/rsrc: fix RLIMIT_MEMLOCK bypass by removing
 cross-buffer accounting

On 1/19/26 4:34 PM, Yuhao Jiang wrote:
> On Mon, Jan 19, 2026 at 11:03 AM Jens Axboe <axboe@...nel.dk> wrote:
>>
>> On 1/19/26 12:10 AM, Yuhao Jiang wrote:
>>> The trade-off is that memory accounting may be overestimated when
>>> multiple buffers share compound pages, but this is safe and prevents
>>> the security issue.
>>
>> I'd be worried that this would break existing setups. We obviously need
>> to get the unmap accounting correct, but in terms of practicality, any
>> user of registered buffers will have had to bump distro limits manually
>> anyway, and in that case it's usually just set very high. Otherwise
>> there's very little you can do with it.
>>
>> How about something else entirely - just track the accounted pages on
>> the side. If we ref those, then we can ensure that if a huge page is
>> accounted, it's only unaccounted when all existing "users" of it have
>> gone away. That means if you drop parts of it, it'll remain accounted.
>>
>> Something totally untested like the below... Yes it's not a trivial
>> amount of code, but it is actually fairly trivial code.
> 
> Thanks, this approach makes sense. I'll send a v3 based on this.

Great, thanks! I think the key is tracking this on the side, and then
a ref to tell when it's safe to unaccount it. The rest is just
implementation details.

-- 
Jens Axboe