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Message-ID: <eac33351-4aba-4eea-8485-a4507a748cd3@lucifer.local>
Date: Tue, 22 Oct 2024 21:58:05 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>, 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 Tue, Oct 22, 2024 at 09:40:51PM +0100, 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.
>
> 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
To clarify - this applies against Andrew's tree [0] in the
mm-hotfixes-unstable branch in order to be applicable against outstanding
hotfix patches for 6.12.
[0]:https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/
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