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b=SCqlr3f1wNRHkLOuv1HecQ44XtVEO+6X15YRRebwA+dQvJ18Sfkfj7nP5OdXOGaVm GXRrN7Nctei5FVzt3ch5aI12VVOU7E10SLw6T2CTYFSL/eScySAxP79fiarmqFXYbf hKAh524nOYtHndkZ2r8Qen6oeVEfXJ7p0UZ/l+6M= Date: Wed, 29 Jul 2026 14:58:19 -0700 From: Andrew Morton To: Zhiling Zou 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 Message-Id: <20260729145819.dfa35a91cd3d04b8f401d43a@linux-foundation.org> In-Reply-To: <87a63846fe9873b1e26e8a7dcafcb21aa8d709fa.1785309651.git.zhilinz@nebusec.ai> References: <87a63846fe9873b1e26e8a7dcafcb21aa8d709fa.1785309651.git.zhilinz@nebusec.ai> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: tc9kg8o5b63xdps7h1gqta91799suuwa X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: F177E80004 X-HE-Tag: 1785362300-210213 X-HE-Meta: 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 NQmamYpW ypMIsUn3aabLty8hVQ3NIad9pGeWFr/k0w0fh7Ox1u1JzoNZXTGcvQYmXCjHTiPMZ5DjwBjSky0JB/opiIaQH6Po8ufPXiowZkjDWj78EEHSijgRW7C1n3/W1FV6mMAaNZQ39ysxSj1EluTpMuFzH4OpOmfMqBIOOywKBZnaK7mUaU7jUpHHHkhusYVExY6bzrOqL6uE/D3hs7+7WiQhswHF16v/yT1K4ze1Anq45bVLUo6nW8KM2pDlqzDCtndezjSJoj2paNcGhM3FtlCPWBZ9LBKz7lHuvuTG1VZU83yBN7pdKi40euuQx1Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 29 Jul 2026 22:07:30 +0800 Zhiling Zou 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?