linux-kernel - Re: [PATCH hotfix 6.12 0/8] fix error handling in mmap

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Message-ID: <2ae61141-9d88-4493-9fc1-245e29dac445@suse.cz>
Date: Wed, 23 Oct 2024 10:37:04 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>, Jann Horn
 <jannh@...gle.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Linus Torvalds <torvalds@...ux-foundation.org>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH hotfix 6.12 0/8] fix error handling in mmap_region() and
 refactor

On 10/22/24 22:40, Lorenzo Stoakes wrote:
> The mmap_region() function is somewhat terrifying, with spaghetti-like
> control flow and numerous means by which issues can arise and incomplete
> state, memory leaks and other unpleasantness can occur.
> 
> A large amount of the complexity arises from trying to handle errors late
> in the process of mapping a VMA, which forms the basis of recently observed
> issues with resource leaks and observable inconsistent state.
> 
> This series goes to great lengths to simplify how mmap_region() works and
> to avoid unwinding errors late on in the process of setting up the VMA for
> the new mapping, and equally avoids such operations occurring while the VMA
> is in an inconsistent state.
> 
> The first four patches are intended for backporting to correct the
> possibility of people encountering corrupted state while invoking mmap()
> which is otherwise at risk of happening.
> 
> After this we go further, refactoring the code, placing it in mm/vma.c in
> order to make it eventually userland testable, and significantly
> simplifying the logic to avoid this issue arising in future.

Are the latter 4 patches thus also intended as hotfix for 6.12, or was it
just due to git applying the same PATCH prefix to the whole series, and the
real intention is 6.13?

> Lorenzo Stoakes (8):
>   mm: avoid unsafe VMA hook invocation when error arises on mmap hook
>   mm: unconditionally close VMAs on error
>   mm: refactor map_deny_write_exec()
>   mm: resolve faulty mmap_region() error path behaviour
>   tools: testing: add additional vma_internal.h stubs
>   mm: insolate mmap internal logic to mm/vma.c
>   mm: refactor __mmap_region()
>   mm: do not attempt second merge for file-backed VMAs
> 
>  include/linux/mman.h             |  21 +-
>  mm/internal.h                    |  44 ++++
>  mm/mmap.c                        | 262 ++------------------
>  mm/mprotect.c                    |   2 +-
>  mm/nommu.c                       |   7 +-
>  mm/vma.c                         | 403 ++++++++++++++++++++++++++++++-
>  mm/vma.h                         | 101 +-------
>  mm/vma_internal.h                |   5 +
>  tools/testing/vma/vma_internal.h | 106 +++++++-
>  9 files changed, 591 insertions(+), 360 deletions(-)
> 
> --
> 2.47.0