linux-kernel - Re: [PATCH fix 6.12] mm: mark mas allocation in vms_abort_munmap_vmas as __GFP

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Message-ID: <c911243f-2c60-44cc-8acd-2eafb3ef4315@suse.cz>
Date: Thu, 17 Oct 2024 11:15:08 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Jann Horn <jannh@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH fix 6.12] mm: mark mas allocation in vms_abort_munmap_vmas
 as __GFP_NOFAIL

On 10/16/24 17:07, Jann Horn wrote:
> vms_abort_munmap_vmas() is a recovery path where, on entry, some VMAs
> have already been torn down halfway (in a way we can't undo) but are
> still present in the maple tree.
> 
> At this point, we *must* remove the VMAs from the VMA tree, otherwise
> we get UAF.
> 
> Because removing VMA tree nodes can require memory allocation, the
> existing code has an error path which tries to handle this by
> reattaching the VMAs; but that can't be done safely.
> 
> A nicer way to fix it would probably be to preallocate enough maple
> tree nodes for the removal before the point of no return, or something
> like that; but for now, fix it the easy and kinda ugly way, by marking
> this allocation __GFP_NOFAIL.

Yes that should be acceptable.

> Fixes: 4f87153e82c4 ("mm: change failure of MAP_FIXED to restoring the gap on failure")
> Signed-off-by: Jann Horn <jannh@...gle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>