From: Andrew Morton <akpm@linux-foundation.org>
To: Zhiling Zou <zhilinz@nebusec.ai>
Cc: linux-mm@kvack.org, baolin.wang@linux.alibaba.com,
hughd@google.com, vega@nebusec.ai
Subject: Re: [PATCH v2 1/1] mm: shmem: reject page-aligned fallocate end overflow
Date: Wed, 29 Jul 2026 14:58:19 -0700 [thread overview]
Message-ID: <20260729145819.dfa35a91cd3d04b8f401d43a@linux-foundation.org> (raw)
In-Reply-To: <87a63846fe9873b1e26e8a7dcafcb21aa8d709fa.1785309651.git.zhilinz@nebusec.ai>
On Wed, 29 Jul 2026 22:07:30 +0800 Zhiling Zou <zhilinz@nebusec.ai> wrote:
> shmem_fallocate() validates offset + len with inode_newsize_ok(), but
> then rounds that end offset up to a page boundary before entering the
> preallocation loop.
>
> For a valid request ending at MAX_LFS_FILESIZE, such as offset = 0 and
> len = LLONG_MAX, adding PAGE_SIZE - 1 to the validated end can overflow
> the signed loff_t used for the rounded end calculation. If that wrapped
> value is then converted into a page index, shmem_fallocate() can enter
> the folio allocation loop with an invalid range.
>
> Cache the already validated end position, use check_add_overflow() when
> rounding it up to a page-aligned byte offset, and reuse the cached end
> for the later seal, shmem_get_folio(), and i_size checks.
Thanks.
AI review:
https://sashiko.dev/#/patchset/87a63846fe9873b1e26e8a7dcafcb21aa8d709fa.1785309651.git.zhilinz@nebusec.ai
Suggests there's a flaw in your change. And it does appear to have
found a significant pre-existing bug in there. Can you please take a
look?
prev parent reply other threads:[~2026-07-29 21:58 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-29 14:07 [PATCH v2 1/1] mm: shmem: reject page-aligned fallocate end overflow Zhiling Zou
2026-07-29 21:58 ` Andrew Morton [this message]
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