Re: [PATCH] mm/hugetlb: Fix use after free when subpool max_hpages accounting is not enabled

[Andrew Morton]

On Wed, 27 Jan 2021 10:08:22 +0800 Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:

> 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.

I made that change, thanks.