linux-kernel - Re: [PATCH] mm/hugetlb: Fix use after free when subpool max

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Date:   Wed, 27 Jan 2021 10:08:22 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/hugetlb: Fix use after free when subpool max_hpages
 accounting is not enabled

On 2021/1/27 8:06, Mike Kravetz wrote:
> On 1/26/21 3:55 AM, Miaohe Lin wrote:
>> When subpool max_hpages accounting is not enabled, used_hpages is always 0
>> and might lead to release subpool prematurely because it indicates no pages
>> are used now while there might be.
> 
> It might be good to say that you need min_hpages accounting (min_size mount
> option) enabled for this issue to occur.  Or, perhaps say this is possible
> if a hugetlbfs filesystem is created with the min_size option and without
> the size option.
> 
> That might better explain the conditions in which a user could see the issue.

So commit log might looks like this ?
"""
If a hugetlbfs filesystem is created with the min_size option and without
the size option, used_hpages is always 0 and might lead to release subpool
prematurely because it indicates no pages are used now while there might
be.

In order to fix this issue, we should check used_hpages == 0 iff max_hpages
accounting is enabled. As max_hpages accounting should be enabled in most
common case, this is not worth a Cc stable.
"""

If so, should I send a V2 or Andrew would kindly do this?
Many thanks.

> 
>> In order to fix this issue, we should check used_hpages == 0 iff max_hpages
>> accounting is enabled. As max_hpages accounting should be enabled in most
>> common case, this is not worth a Cc stable.
> 
> I agree that such a combination of mount options is very uncommon.
> 
>>
>> Signed-off-by: Hongxiang Lou <louhongxiang@...wei.com>
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>>  mm/hugetlb.c | 16 +++++++++++++---
>>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> Thanks,
> 
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
> 

Many thanks for review.