linux-kernel - Re: [PATCH 6.1.y 0/4] fix error handling in mmap

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Message-ID: <1fd407b1-c061-4f24-b78a-ab90fa5d78d5@suse.cz>
Date: Fri, 15 Nov 2024 20:11:35 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, stable@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 "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>, Catalin Marinas <catalin.marinas@....com>,
 Will Deacon <will@...nel.org>, Mark Brown <broonie@...nel.org>,
 "David S . Miller" <davem@...emloft.net>,
 Andreas Larsson <andreas@...sler.com>,
 "James E . J . Bottomley" <James.Bottomley@...senPartnership.com>,
 Helge Deller <deller@....de>
Subject: Re: [PATCH 6.1.y 0/4] fix error handling in mmap_region() and
 refactor (hotfixes)

On 11/15/24 13:40, Lorenzo Stoakes wrote:
> Critical fixes for mmap_region(), backported to 6.1.y.
> 
> Some notes on differences from upstream:
> 
> * We do NOT take commit 0fb4a7ad270b ("mm: refactor
>   map_deny_write_exec()"), as this refactors code only introduced in 6.2.
> 
> * We make reference in "mm: refactor arch_calc_vm_flag_bits() and arm64 MTE
>   handling" to parisc, but the referenced functionality does not exist in
>   this kernel.
> 
> * In this kernel is_shared_maywrite() does not exist and the code uses
>   VM_SHARED to determine whether mapping_map_writable() /
>   mapping_unmap_writable() should be invoked. This backport therefore
>   follows suit.
> 
> * The vma_dummy_vm_ops static global doesn't exist in this kernel, so we
>   use a local static variable in mmap_file() and vma_close().

Seems adding 9a9d0b829901 ("mm: move dummy_vm_ops out of a header") as
prerequisity would have been less work, but I didn't find a bug in your
adjustments so seems fine to me.

> 
> * Each version of these series is confronted by a slightly different
>   mmap_region(), so we must adapt the change for each stable version. The
>   approach remains the same throughout, however, and we correctly avoid
>   closing the VMA part way through any __mmap_region() operation.
> 
> * This version of the kernel uses mas_preallocate() rather than the
>   vma_iter_prealloc() wrapper and mas_destroy() rather than the
>   vma_iter_free() wrapper, however the logic of rearranging the positioning
>   of these remains the same, as well as avoiding the iterator leak we
>   previously had on some error paths.
> 
> Lorenzo Stoakes (4):
>   mm: avoid unsafe VMA hook invocation when error arises on mmap hook
>   mm: unconditionally close VMAs on error
>   mm: refactor arch_calc_vm_flag_bits() and arm64 MTE handling
>   mm: resolve faulty mmap_region() error path behaviour

Aside from the suspected memory leak I reported for 4/4,

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

>  arch/arm64/include/asm/mman.h |  10 ++-
>  include/linux/mman.h          |   7 +-
>  mm/internal.h                 |  19 ++++++
>  mm/mmap.c                     | 119 ++++++++++++++++++----------------
>  mm/nommu.c                    |   9 ++-
>  mm/shmem.c                    |   3 -
>  mm/util.c                     |  33 ++++++++++
>  7 files changed, 129 insertions(+), 71 deletions(-)
> 
> --
> 2.47.0